**Meet the editor**

Suzuki Toshiaki, DMSc, is a physical therapist and presently a professor at the Graduate School of Kansai University of Health Sciences, Osaka, Japan. As an instructor at the Department of Physical Therapy, College of Medical Technology, Kyoto University (1987–1994), he learned electromyography methods from Tetsuji Fujiwara, MD, and Jun Kimura, MD, professors emeriti (Kyoto Universi-

ty). He has extensively studied electromyography's use in physical therapy. His interests include fundamental research on the effects of neurological physical therapy using electromyography, especially spinal neural function using evoked F-wave electromyography and the development of Acupoint Stimulation Physical Therapy (ASPT), which combines physical therapy and acupuncture. The effect of ASPT is being investigated using electromyography and is expected to develop into a new physical therapy method. He has many original publications and books on these subjects.

## Contents

#### **Preface XI**

Chapter 12 **Application of Robotics for Therapeutic Exercise of Neural Disorder 215** Yasuhiko Hatanaka, Kazuki Yamaguchi, Koichi Saito and Satomi

Tada

## Preface

Chapter 8 **Non-Invasive Brain Stimulation (TMS/tDCS) and Rehabilitation**

Chapter 9 **Neuroscience-Based Rehabilitation for Stroke Patients 137**

Tadamitsu Matsuda, Atsushi Manji, Kazu Amimoto, Akira Inaba and

**for Stroke and Parkinson's 121**

Takayuki Kodama and Hideki Nakano

Chapter 11 **Neuromuscular Diseases and Rehabilitation 175**

Chapter 12 **Application of Robotics for Therapeutic Exercise of Neural**

Yasuhiko Hatanaka, Kazuki Yamaguchi, Koichi Saito and Satomi

Chapter 10 **Physical Therapy for Cerebellar Ataxia 157**

Yoshiaki Wada

**VI** Contents

Akiyoshi Matsugi

**Disorder 215**

Tada

Yasemin Parlak Demir

Physical therapy, also known as physiotherapy, is a physical medicine and rehabilitation specialization that, by using mechanical force and movements, remedies impairments and promotes mobility, function, and quality of life through examination, diagnosis, prognosis, and physical intervention. In addition to clinical practice, other activities encompassed by the physical therapy profession include research, education, consultation, and administra‐ tion. Physical therapy services may be provided alongside, or in conjunction with, other medical services. It is performed by physical therapists (known as physiotherapists in many countries) with the help of other medical professionals.

This book consists of 12 manuscripts by professionals from all around the world. It includes manuscripts on the effects of physical therapy. These manuscripts show the basis for clinical use of observation and motor imagery.

The book includes also chapters related to the spinal neural function and the somatosensory area during voluntary movements. These manuscripts show us appropriate methods for the performance of motor tasks.

Finally, the book includes chapters for neuroscience-based rehabilitation using motor image‐ ry and tDCS for stroke patients, physical therapy for cerebellar ataxia and neuromuscular disease, and applications of robotics for stroke and cerebral palsy.

I am very pleased to be the editor of this book, as all chapters are excellent and open up new directions for physical therapists in the field of neurological physical therapy.

> **Professor Toshiaki Suzuki, DMSc** Graduate School of Kansai University of Health Sciences, Osaka, Japan

## **The Study of Action Observation Therapy in Neurological Diseases: A Few Technical Considerations The Study of Action Observation Therapy in Neurological Diseases: A Few Technical Considerations**

## Julio Plata-Bello Julio Plata-Bello

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67651

#### **Abstract**

Action observation therapy (AOT) is a developing neurorehabilitative tool, which is based on the existence of the mirror neuron system (MNS). This neural network involves motor regions, and its main feature is that it is activated not only during the execution of an action, but also during the observation of the same action. Bearing in mind this "dual" activation, the AOT proposes that motor symptoms of different neurological disorders can improve with the observation and imitation of different actions. While several studies have shown the benefits of this therapy, others have been less favorable indicating a lack of clarity in the field. The present study focuses on previously undiscussed aspects regarding this therapy: from the kind of actions used in the therapy to the scales that should be used to measure the results of AOT. Differences and similarities between virtual reality-based therapies and AOT are also discussed. The considerations made here about all such aspects may be useful for future studies and possible applications of AOT.

**Keywords:** mirror neurons, neurological rehabilitation, rehabilitation interventions, action observation, motor recovery

## **1. Introduction**

Action observation therapy (AOT) is based on the well-known "mirror mechanism." AOT alludes to the activation of motor-related areas not only when an action is performed, but also when the action is observed [1]. This mechanism was first described in the premotor cortex of the macaque [2], and over the last two decades, several studies have focused on the identification, description and characterization of the human brain regions that present this mechanism [3–5]. Nowadays, there is much agreement about the existence of a neural network formed by regions that present the "mirror mechanism." The most consistent regions are located in

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the frontal lobe [mainly in the inferior frontal gyrus (IFG)] and in the posterior parietal lobe [mainly in the inferior parietal lobule (IPL)] [1, 4], though there are other regions that may also be involved [6, 7]. This brain network is the so-called mirror neuron system (MNS) (**Figure 1**).

The dual activation of the MNS has been associated with the ability to understand the actions performed by others [3, 8]. Bearing this in mind, it is easy to deduce that the MNS is essential for imitation and, eventually, for action learning [9–11]. Several experiments have provided some evidence in this respect and have led to the suggestion of the possible role of action observation (i.e., MNS activation) in motor rehabilitation. Effectively, the activation of motor regions during the simple observation of an action may result in an improvement of motor impairment; this is the AOT hypothesis. However, the MNS is associated not only with motor functions, but also with social cognition. Many authors agree in considering the involvement of the MNS in social interaction and in the relationship between people and the environment [4, 12]. This consideration makes the AOT not only a motor rehabilitation program, but also a functional recovery program.

**Figure 1.** The MNS in humans. Many functional studies have shown that many brain regions present mirror properties. Apart from premotor cortex (PMC), parietal and temporal regions are also activated when an action is executed or observed and this is clearly related with the important role that mirror neurons seem to play in many aspects of social cognition (language, empathy, learning process, etc.). Because of this, it has been suggested that developmental MNS dysfunction leads to disordered social cognition in humans, including autism spectrum disorders. Anyway, the most studied areas that present mirror properties in humans are the inferior frontal gyrus (IFG) corresponding to BA 44 and inferior parietal lobule (IPL), corresponding to BA 40. Both form the core of the known parietal-frontal mirror neuron system (MNS). The superior temporal sulcus (STS) is consistently activated during the observation of human movements and seems to play a prominent role in the flux of information to the MNS.

Bearing in mind only neurological diseases, stroke is, unmistakably, the most common neurological disease where AOT has been tested. Motor impairment and aphasia were the most common features of the stroke patients included in trials and prospective observational studies [13–20]. For both clinical conditions, the majority of the studies reported a clear benefit of AOT, with a maintained improvement in the motor condition and the functional status. In fact, the benefit of this therapy has been remarked on in a recent evidenced-based review of the literature concerning the effect of AOT in upper limb dysfunction after stroke [21].

AOT has also been used in other movement disorders such as Parkinson's disease and cerebral palsy, though the number of studies that have focused on these diseases is much lower than those focused on stroke. In any case, the application of AOT leads to an improvement in gait and bradykinesia in Parkinsonian patients [22–24] and in the functional status in cerebral palsy's infants [25]. Finally, cognitive benefits have been reported after the application of AOT in Alzheimer's disease [26].

New and different studies about AOT need to be performed in order to properly identify the role of this therapy in the rehabilitation of neurological disorders. Some weaknesses in the current literature about AOT can be identified. For example, most of the previously cited studies included patients with a chronic evolution of their diseases (more than 6 months after the onset) and not in the acute or subacute phase of the disease, where the therapy might also show efficacy (or even more). Furthermore, the number of patients is highly variable between the different studies and the differences in the period where patients were exposed between the different studies are large. However, these methodological aspects are not the only ones that must be considered when AOT is going to be applied. In the present work, we stress the importance of adequately selecting the actions to be used during therapy as well as the correct scale for evaluating the results of AOT. The consideration of these aspects in future studies may help to provide a better understanding of the MNS and to know the real impact of the therapy in patient's recovery. This study also discusses the differences and similarities that exist between virtual reality-based therapies, an innovative approach that is being increasingly applied in rehabilitation centers. Finally, future perspectives about AOT research are proposed.

## **2. Which actions should be used in AOT?**

the frontal lobe [mainly in the inferior frontal gyrus (IFG)] and in the posterior parietal lobe [mainly in the inferior parietal lobule (IPL)] [1, 4], though there are other regions that may also be involved [6, 7]. This brain network is the so-called mirror neuron system (MNS) (**Figure 1**). The dual activation of the MNS has been associated with the ability to understand the actions performed by others [3, 8]. Bearing this in mind, it is easy to deduce that the MNS is essential for imitation and, eventually, for action learning [9–11]. Several experiments have provided some evidence in this respect and have led to the suggestion of the possible role of action observation (i.e., MNS activation) in motor rehabilitation. Effectively, the activation of motor regions during the simple observation of an action may result in an improvement of motor impairment; this is the AOT hypothesis. However, the MNS is associated not only with motor functions, but also with social cognition. Many authors agree in considering the involvement of the MNS in social interaction and in the relationship between people and the environment [4, 12]. This consideration makes the AOT not only a motor rehabilitation program, but also a functional recovery program.

2 Neurological Physical Therapy

**Figure 1.** The MNS in humans. Many functional studies have shown that many brain regions present mirror properties. Apart from premotor cortex (PMC), parietal and temporal regions are also activated when an action is executed or observed and this is clearly related with the important role that mirror neurons seem to play in many aspects of social cognition (language, empathy, learning process, etc.). Because of this, it has been suggested that developmental MNS dysfunction leads to disordered social cognition in humans, including autism spectrum disorders. Anyway, the most studied areas that present mirror properties in humans are the inferior frontal gyrus (IFG) corresponding to BA 44 and inferior parietal lobule (IPL), corresponding to BA 40. Both form the core of the known parietal-frontal mirror neuron system (MNS). The superior temporal sulcus (STS) is consistently activated during the observation of human movements

and seems to play a prominent role in the flux of information to the MNS.

One major issue about AOT is the kind of action that should be used in order to get the maximum benefit. Most of the actions that have been employed in AOT studies consist of upper limb transitive actions (i.e., actions with object interaction, e.g., using a pencil). These are usually daily actions that have been selected on the basis of their ecological value [27]. This kind of action has been shown to have increased MNS activity in neuroimaging studies [15, 28] and corticospinal facilitation in transcranial magnetic stimulation (TMS) [29, 30].

Although the benefits of AOT have been demonstrated with the use of transitive actions, the use of intransitive ones (i.e., actions without object interaction, e.g., the opposition of the index finger and the thumb as the pantomime of a precision grasping) may also be considered for use in this therapy. Intransitive actions lead to an activation of the human MNS (there is new evidence of this activation in primates too) in a more restrictive way than transitive actions do [31, 32]. In fact, the activity of the MNS when intransitive actions are observed tends to predominantly activate posterior parietal regions more than premotor areas [31, 33]. Minor activation of the MNS does not have to mean that an AOT based on these actions had less benefit than using transitive ones. It is known that part of the brain activity obtained with the use of transitive actions is due to the presence of an object and a more complex scenario where the action takes part [34]. In this respect, many patients with neurological disorders may have attention deficits or less capacity to follow the action continuously, because there are many factors that catch the observer's attention (e.g., the object features) and they may become cognitively overloaded. Furthermore, when patients are asked to imitate the motor actions, the imitation of simple and intransitive actions would be effortless than the performance of complex and transitive ones. Consequently, future studies should incorporate intransitive actions to those which patients must observe to evaluate the efficacy of the AOT using these actions. Although they will lead to less brain activity, the patient can be more focused on the effector as well as on the kinematics of the action, and neither on the object which the effector interacts with nor on the context where the action takes place.

On the other hand, another factor that must be considered in AOT is the visual perspective from which the motor acts of others are observed. It has been demonstrated that the majority of mirror neurons in the monkey premotor cortex are view-dependent (i.e., they are only activated when the action is presented in a specific visual perspective) [35, 36] and, depending on the point of view, action observation leads to different activations of the MNS [37]. In this sense, certain evidence exists that an egocentric view (i.e., first-person perspective) of an action leads to higher brain activity than a third-person view [30] (**Figure 2**). Moreover, studies in monkeys have revealed the existence of some subcategories of mirror neurons that are selective for specific space positions, right or left hand, and for specific directions [2, 38]. Although these

**Figure 2.** Different visual perspectives. First-person perspective (A) and third-person perspective (B) of an intransitive motor action (index to thumb opposition task). First-person perspective seems to conduct to higher MNS activity than a third-person view.

properties have been less studied in the human MNS, its presence in non-human primates makes it easy to assume the existence of this diversity among the mirror neurons of human beings. Thus, the MNS is important for visuospatial and visuoperceptive abilities. Bearing this in mind, patients who are candidates for AOT should be previously tested in these functions with proper neuropsychological assessment. This evaluation may allow the adaption of the kind of actions that are shown to the patient in order to achieve better and faster results.

### **3. Measuring AOT results: what matters?**

of this activation in primates too) in a more restrictive way than transitive actions do [31, 32]. In fact, the activity of the MNS when intransitive actions are observed tends to predominantly activate posterior parietal regions more than premotor areas [31, 33]. Minor activation of the MNS does not have to mean that an AOT based on these actions had less benefit than using transitive ones. It is known that part of the brain activity obtained with the use of transitive actions is due to the presence of an object and a more complex scenario where the action takes part [34]. In this respect, many patients with neurological disorders may have attention deficits or less capacity to follow the action continuously, because there are many factors that catch the observer's attention (e.g., the object features) and they may become cognitively overloaded. Furthermore, when patients are asked to imitate the motor actions, the imitation of simple and intransitive actions would be effortless than the performance of complex and transitive ones. Consequently, future studies should incorporate intransitive actions to those which patients must observe to evaluate the efficacy of the AOT using these actions. Although they will lead to less brain activity, the patient can be more focused on the effector as well as on the kinematics of the action, and neither on the object which the effector interacts with nor on the context where the action takes place.

On the other hand, another factor that must be considered in AOT is the visual perspective from which the motor acts of others are observed. It has been demonstrated that the majority of mirror neurons in the monkey premotor cortex are view-dependent (i.e., they are only activated when the action is presented in a specific visual perspective) [35, 36] and, depending on the point of view, action observation leads to different activations of the MNS [37]. In this sense, certain evidence exists that an egocentric view (i.e., first-person perspective) of an action leads to higher brain activity than a third-person view [30] (**Figure 2**). Moreover, studies in monkeys have revealed the existence of some subcategories of mirror neurons that are selective for specific space positions, right or left hand, and for specific directions [2, 38]. Although these

**Figure 2.** Different visual perspectives. First-person perspective (A) and third-person perspective (B) of an intransitive motor action (index to thumb opposition task). First-person perspective seems to conduct to higher MNS activity than

a third-person view.

4 Neurological Physical Therapy

One of the most important aspects when considering AOT is to adequately evaluate the results. The use of an appropriate scale or index is a basic requisite to analyze the efficacy of any rehabilitative therapy. Previous studies have reported the efficacy of the AOT in terms of changes in scales that measured specific clinical aspects of each neurological disease. For instance, some stroke-based studies expressed the efficacy of AOT with changes in Upper Extremity Fugl-Meyer Motor Assessment (FMA) and Functional Test of the Hemiparetic Upper Extremity (FTHUE) [20]; similarly, the application of AOT in Parkinson's disease patients was measured with a 39-item Parkinson Disease Questionnaire (PDQ-39) [24]. Although the specific scales are vital for understanding the effect of MNS therapy in the clinical symptoms of each neurological disease, the broad implications of AOT (considering its effect on the MNS with motor and cognitive implications) mean that these scales are restricted. Moreover, these scales should also be versatile enough to be applied to the majority of the spectrum of neurological diseases where AOT may be applied. Thus, it seems reasonable to propose a more general scale or index to evaluate the results of AOT in terms of functional recovery.

Functioning is a generic term defined by the World Health Organization (WHO), which includes the positive aspects of the interaction between an individual (with a certain health condition) and the contextual factors (personal and environmental factors). This leads to a definition of disability as the restriction of a person's functioning. Neurorehabilitative approaches must converge in a recovery in the functioning that may have been lost as a result of the disease. Therefore, the efficacy of this kind of therapy has to be measured by functional scales.

There are several functional scales described in the literature. Bearing in mind its extensive applicability in neurological diseases, broad extended use and adaptability, the Barthel Index (BI) can be considered as a trustworthy scale for evaluating AOT results. The BI was designed in 1965 by Mohoney and Barthel [39] and has been subsequently modified by many others. The modification made by Granger et al. [40] should be mentioned as it is probably the most used version of the BI nowadays. The BI modified (BIm) consists of the evaluation of the independency degree when a patient performs 15 basic daily life activities (BDLA). Granger et al. grouped the activities into two subscales: one measuring the capacity to take care of themselves and the other determining the degree of mobility (**Table 1**). The BIm is a highly sensitive, valid and feasible, which is able to detect progress or impairment during the evolution of a rehabilitation program [41]. Furthermore, it is an inexpensive tool, which does not take up much of the examiner's time.

**Table 1.** Barthel Index modified by Granger et al. Adapted from Granger et al. [40].

However, the evaluation of the capacity to perform the BDLA may not be enough to appropriately measure the impact of the AOT. "Instrumental daily life activities" (IDLA) and "advanced daily life activities" (ADLA) have been defined as activities that allow a person to be independent in the community (IDLA) (e.g., going to the supermarket, cooking) and to develop a social role (ADLA) (e.g., working, practicing sports, religion). The measurement of the capacity to develop these activities would provide a more holistic picture of the patient's situation before and after the application of AOT. It would be interesting to evaluate the results of AOT using specific scales for IDLA and ADLA, because the MNS is clearly involved in the normal development of these activities.

One of the scales for IDLA assessment is the Lawton and Brody scale, which consists of eight items related to daily activities (e.g., use of transport) which are asked directly to the patient or the caregiver [42]. It is a highly sensitive scale and has a high inter- and intra-observer correlation coefficient. However, the main disadvantage of this scale is that it was conceived for the elderly population, and thus, its application might be restricted.

Furthermore, it should be recognized that the evaluation of IDLA and ADLA is more complex than other evaluations and such activities are influenced by the culture and the geographical environment of the patient. Therefore, some effort needs to be made for testing new scales to approach the evaluation of IDLA and ADLA and apply them (with BDLA scales) to the measurement of AOT impact.

## **4. AOT and virtual reality: two heads of the same coin**

AOT is not the only rehabilitative tool that has been investigated in the last decade to improve the functional status of patients with neurological disorders. The application of virtual reality (VR) approaches in the field of rehabilitation is extensively reported, and it has been shown to have certain benefits, not only in the recovery of motor dysfunctions [43], but also in improving cognitive impairment [44, 45]. VR therapies are based on the generation of a real-time threedimensional environment that makes the patients feels as if they are in a real situation [46]. Normally, the patient is situated in front of a monitor and is required to perform actions with the impaired limb (or with the non-impaired limb when the deficit is notable). These actions are recognized by a movement sensor, and the patient receives the feedback by means of the monitor, observing different movements or consequences of the performed actions. The feedback will depend on which VR program has been initiated. For instance, a VR program may consist of a box moving from one side to the other; the patient performs an action and observes the displacement of the boxes on the screen). These VR approaches have demonstrated their usefulness in several neurological disorders [43, 47–49], with stroke being the subject of the largest number of studies. In fact, a recent Cochrane meta-analysis concluded that VR leads to an improvement in upper limb function and recommended its use as a complementary therapy to the usual therapy for improving the activity of daily living function [50].

VR therapy has some aspects in common with AOT. The feedback in both therapies consists of an observation task (although the feedback of VR is usually over dimensioned); moreover, patients can be requested to interact with the elements they observe, with an imitation (AOT) or by trying to modify a condition in the virtual environment. Thus, VR and AOT modulate the MNS to achieve an improvement in the functional condition of patients. In this respect, some studies have shown the presence of an intense MNS activity during VR tasks [51, 52].

However, the evaluation of the capacity to perform the BDLA may not be enough to appropriately measure the impact of the AOT. "Instrumental daily life activities" (IDLA) and "advanced daily life activities" (ADLA) have been defined as activities that allow a person to be independent in the community (IDLA) (e.g., going to the supermarket, cooking) and to develop a social role (ADLA) (e.g., working, practicing sports, religion). The measurement of the capacity to develop these activities would provide a more holistic picture of the patient's situation before and after the application of AOT. It would be interesting to evaluate the results of AOT using specific scales for IDLA and ADLA, because the MNS is clearly involved

**Independent Assistance Dependent**

Drinking using a glass 4 0 0 Eating 6 0 0 Dressing the upper part of the body 5 3 0 Dressing the lower part of the body 7 4 0 Putting on prosthesis 0 −2 0 Tidying up 5 0 0 Bathing 6 0 0 Urine control 10 5 0 Fecal control 10 5 0

Sitting/getting up from a chair/bed 15 7 0 Use of the toilet 6 3 0 Getting in/out to the shower1 1 0 0 Walking 50 m 15 10 0 Going down/upstairs 10 5 0 Propelling a wheelchair 5 0 0

in the normal development of these activities.

0–20 Complete disabled 21–60 Severe disabled 61–90 Moderate disabled 91–99 Slight disabled 100 Independent

**Table 1.** Barthel Index modified by Granger et al. Adapted from Granger et al. [40].

**Personal care**

6 Neurological Physical Therapy

**Mobility**

**Score**

However, although these therapies share common features in the conditions they use, as well as the neural substrates they take advantage of, there are important feasibility and applicability differences. On the one hand, VR therapy requires a more sophisticated informatics structure than AOT; thus, it may be less efficient and makes this therapy less practical for use at home. On the other hand, the instructions and the tasks of VR therapies are more complex than those applied in AOT (i.e., simply observing or imitating a movement). Therefore, although VR and AOT may be complementary rehabilitation tools, AOT may be more widely used than VR in different socioeconomic environments.

## **5. Future perspectives**

The road that AOT has to travel until it can be considered a standard therapy in neurorehabilitation is still long. Although some randomized trials have been published reporting the efficacy of this therapy in stroke, Parkinson's disease and cerebral palsy patients, new studies are necessary (considering the heterogeneity in the scales used for measuring the efficacy and in the period of treatment). Furthermore, other neuropathological conditions should be considered in such trials. For example, multiple sclerosis or traumatic brain injury patients could also benefit from AOT, but no randomized trials with this kind of patients have been performed to date.

On the other hand, apart from the aspects that have been discussed above, it would also be interesting if new studies reported the results of neurofunctional studies (i.e., neuroimaging and/or other functional tests). It would provide much information about the functioning of the MNS in different pathological conditions as well as the plastic changes in the brain that may be associated with the use of AOT.

Further study of AOT may generate a new weapon in the armory against the functional and social limitations produced by neurological disorders. The decrease of such limitations is clearly associated with an improvement in the quality of life and survival periods of the patients, thanks to the reduction of complication rates (associated with the aforementioned limitations). Therefore, new and appropriate research is needed to convert the AOT in a standard therapy in our hospitals and rehabilitative centers.

## **Acknowledgements**

We would like to thank all members of the research group "Neurochemistry and Neuroimaging" of the University of La Laguna for their ideas and contributions to the preparation of this chapter.

## **Author details**

Julio Plata-Bello1,2

Address all correspondence to<EMAIL_ADDRESS>
1 Department of Neurosurgery, Hospital Universitario de Canarias, Spain

2 Magnetic Resonance Imaging Service for Biomedical Research, University of La Laguna, Spain

## **References**

use at home. On the other hand, the instructions and the tasks of VR therapies are more complex than those applied in AOT (i.e., simply observing or imitating a movement). Therefore, although VR and AOT may be complementary rehabilitation tools, AOT may be more widely

The road that AOT has to travel until it can be considered a standard therapy in neurorehabilitation is still long. Although some randomized trials have been published reporting the efficacy of this therapy in stroke, Parkinson's disease and cerebral palsy patients, new studies are necessary (considering the heterogeneity in the scales used for measuring the efficacy and in the period of treatment). Furthermore, other neuropathological conditions should be considered in such trials. For example, multiple sclerosis or traumatic brain injury patients could also benefit from AOT, but no randomized trials with this kind of patients have been performed to date.

On the other hand, apart from the aspects that have been discussed above, it would also be interesting if new studies reported the results of neurofunctional studies (i.e., neuroimaging and/or other functional tests). It would provide much information about the functioning of the MNS in different pathological conditions as well as the plastic changes in the brain that

Further study of AOT may generate a new weapon in the armory against the functional and social limitations produced by neurological disorders. The decrease of such limitations is clearly associated with an improvement in the quality of life and survival periods of the patients, thanks to the reduction of complication rates (associated with the aforementioned limitations). Therefore, new and appropriate research is needed to convert the AOT in a stan-

We would like to thank all members of the research group "Neurochemistry and Neuroimaging" of the University of La Laguna for their ideas and contributions to the prepa-

2 Magnetic Resonance Imaging Service for Biomedical Research, University of La Laguna,

used than VR in different socioeconomic environments.

**5. Future perspectives**

8 Neurological Physical Therapy

may be associated with the use of AOT.

**Acknowledgements**

ration of this chapter.

**Author details**

Julio Plata-Bello1,2

Spain

dard therapy in our hospitals and rehabilitative centers.

Address all correspondence to<EMAIL_ADDRESS>
1 Department of Neurosurgery, Hospital Universitario de Canarias, Spain

[29] Enticott PG, Kennedy H a, Bradshaw JL, et al. Understanding mirror neurons: evidence for enhanced corticospinal excitability during the observation of transitive but not intransitive hand gestures. Neuropsychologia 2010;48:2675–80. doi:10.1016/j. neuropsychologia.2010.05.014

[16] Franceschini M, Agosti M, Cantagallo A, et al. Mirror neurons: action observation treatment as a tool in stroke rehabilitation. Eur J Phys Rehabil Med 2010;46:517–23.

[17] Franceschini M, Ceravolo MG, Agosti M, et al. Clinical relevance of action observation in upper-limb stroke rehabilitation: a possible role in recovery of functional dexterity. A randomized clinical trial. Neurorehabil Neural Repair 2012;26:456–62.

[18] Michielsen ME, Selles RW, van der Geest JN, et al. Motor recovery and cortical reorganization after mirror therapy in chronic stroke patients: a phase II randomized controlled

trial. Neurorehabil Neural Repair 2011;25:223–33. doi:10.1177/1545968310385127 [19] Sampson M, Shau Y-W, King MJ. Bilateral upper limb trainer with virtual reality for post-stroke rehabilitation: case series report. Disabil Rehabil Assist Technol 2012;7:55–

[20] Sugg K, Müller S, Winstein C, et al. Does action observation training with immediate physical practice improve hemiparetic upper-limb function in chronic stroke?

[21] Kim K. Action observation for upper limb function after stroke: evidence-based review of randomized controlled trials. J Phys Ther Sci 2015;27:3315–7. doi:10.1589/jpts.27.3315

[22] Pelosin E, Avanzino L, Bove M, et al. Action observation improves freezing of gait in patients with Parkinson's disease. Neurorehabil Neural Repair 2010;24:746–52.

[23] Pelosin E, Bove M, Ruggeri P, et al. Reduction of bradykinesia of finger movements by a single session of action observation in Parkinson disease. Neurorehabil Neural Repair

[24] Jaywant A, Ellis TD, Roy S, et al. Randomized controlled trial of a home-based action observation intervention to improve walking in Parkinson disease. Arch Phys Med

[25] Buccino G, Arisi D, Gough P, et al. Improving upper limb motor functions through action observation treatment: a pilot study in children with cerebral palsy. Dev Med

[26] Eggermont LHP, Swaab DF, Hol EM, et al. Observation of hand movements by older persons with dementia: effects on cognition: a pilot study. Dement Geriatr Cogn Disord

[27] Buccino G. Action observation treatment: a novel tool in neurorehabilitation. Philos

[28] Filimon F, Nelson JD, Hagler DJ, et al. Human cortical representations for reaching: mirror neurons for execution, observation, and imagery. Neuroimage 2007;37:1315–28.

Trans R Soc Lond B Biol Sci 2014;369:20130185. doi:10.1098/rstb.2013.0185

Neurorehabil Neural Repair 2015;29:807–17. doi:10.1177/1545968314565512

doi:10.1177/1545968311427406

10 Neurological Physical Therapy

62. doi:10.3109/17483107.2011.562959

doi:10.1177/1545968310368685

2013;27:552–60. doi:10.1177/1545968312471905

2009;27:366–74. doi:10.1159/000209311

doi:10.1016/j.neuroimage.2007.06.008

Rehabil 2016;97:665–73. doi:10.1016/j.apmr.2015.12.029

Child Neurol 2012;54:822–8. doi:10.1111/j.1469-8749.2012.04334.x

#### **Motor Imagery and Action Observation as Effective Tools for Physical Therapy Motor Imagery and Action Observation as Effective Tools for Physical Therapy**

Hideki Nakano and Takayuki Kodama Hideki Nakano and Takayuki Kodama

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67519

#### **Abstract**

[43] Yoon J, Chun MH, Lee SJ, et al. Effect of virtual reality-based rehabilitation on upperextremity function in patients with brain tumor: controlled trial. Am J Phys Med Rehabil

[44] García-Betances RI, Jiménez-Mixco V, Arredondo MT, et al. Using virtual reality for cognitive training of the elderly. Am J Alzheimers Dis Other Demen 2015;30:49–54.

[45] Yang S, Chun MH, Son YR. Effect of virtual reality on cognitive dysfunction in patients with brain tumor. Ann Rehabil Med 2014;38:726–33. doi:10.5535/arm.2<IP_ADDRESS>6 [46] Holden MK. Virtual environments for motor rehabilitation: review. Cyberpsychol Behav

[47] Liao Y-Y, Yang Y-R, Cheng S-J, et al. Virtual reality-based training to improve obstacle-crossing performance and dynamic balance in patients with Parkinson's disease.

[48] Eftekharsadat B, Babaei-Ghazani A, Mohammadzadeh M, et al. Effect of virtual realitybased balance training in multiple sclerosis. Neurol Res 2015;37:539–44. doi:10.1179/174

[49] Lloréns R, Gil-Gómez J-A, Alcañiz M, et al. Improvement in balance using a virtual reality-based stepping exercise: a randomized controlled trial involving individuals with

[50] Laver KE, George S, Thomas S, et al. Virtual reality for stroke rehabilitation. Cochrane

[51] Prochnow D, Bermúdez i Badia S, Schmidt J, et al. A functional magnetic resonance imaging study of visuomotor processing in a virtual reality-based paradigm: rehabilita-

[52] Modroño C, Plata-Bello J, Zelaya F, et al. Enhancing sensorimotor activity by controlling virtual objects with gaze. PLoS One 2015;10:e0121562. doi:10.1371/journal.pone.0121562

Neurorehabil Neural Repair 2015;29:658–67. doi:10.1177/1545968314562111

chronic stroke. Clin Rehabil 2015;29:261–8. doi:10.1177/0269215514543333

tion gaming system. Eur J Neurosci 2013;37:1441–7. doi:10.1111/ejn.12157

2015;94:449–59. doi:10.1097/PHM.0000000000000192

2005;8:187–211; discussion 212–9. doi:10.1089/cpb.2005.8.187

doi:10.1177/1533317514545866

12 Neurological Physical Therapy

3132815Y.0000000013

database Syst Rev 2015;2:CD008349.

Motor imagery and action observation facilitate motor recovery of patients because both the motor imagery and the action observation share the activation of cortical neural networks implicated in movement execution. Specifically, imagery, observation, and execution activate the medial parietal area of the brain located between the parieto‐ occipital sulcus and the posterior end of the cingulate sulcus. This chapter reviews the neural mechanisms and clinical studies of motor imagery and action observation and discusses the applications in physical therapy.

**Keywords:** action observation, motor imagery, physical therapy

### **1. Introduction**

Motor imagery and action observation have been proven as effective tools in rehabilitation [1]. Motor imagery is a cognitive process in which a subject only imagines completing a movement, without tensing any muscles (**Figure 1(a)**) [2]. While motor imagery alone can improve motor performance [3], it is particularly effective when associated with physical practice [4] as compared to physical practice alone. Hétu et al. reported the neural network of motor imagery using ALE meta‐analysis [5]. The meta‐analysis examined the general pat‐ tern of consistent activations during motor imagery and revealed several large clusters of activated tissue spanning over both hemispheres of the brain. In the frontal lobes, the bilat‐ eral inferior frontal gyri (IFG, including the pars opercularis), precentral gyrus (PcG), middle

and reproduction in any medium, provided the original work is properly cited.

**Figure 1.** Motor imagery and action observation [2]. Human brain activity during motor imagery (a) and action observation (b). (a) Brain areas activated during kinesthetic and visual motor imagery. The pattern of activity includes the following regions: ventral and dorsal part of the premotor cortex (PMC); the supplementary motor area (SMA); anterior cingulate cortex (aCC); superior parietal lobule (sPL) and inferior parietal lobule (IPL); precuneus; basal ganglia (BG); and cerebellum. (b) The complex brain network ("mirror neuron system") involved in action observation: the ventral premotor cortex (vPMC), posterior part of the inferior frontal gyrus (pIFG), rostral part of the inferior parietal lobule (rIPL), and posterior superior temporal sulcus (pSTS).

frontal gyrus (MfG), supplementary motor area (SMA), and regions of the anterior insula were regions consistently activated during motor imagery. In the parietal lobes, the bilateral superior parietal lobule (SPL), supramarginal gyrus (SMG), and left inferior parietal lobule (IPL) and, in the subcortical regions, the left putamen, right thalamus, and pallidum were activated. Finally, the areas VI (bilateral) and the vermis of the cerebellum (CB) were also found to be consistently activated.

When a subject observes a specific action being performed, activation of the same neu‐ ral structures used for the movement pattern is also repeated in the subject (**Figure 1(b)**) [2]. The neurophysiological basis of action observation is represented by the discovery of mirror neurons in the cerebral cortex of monkeys [6, 7]. These neurons discharge dur‐ ing both the execution of goal‐directed actions and the observation of other individuals performing similar movements. The definition of the mirror neuron system (MNS) is the area that comprises the cerebral areas containing mirror neurons. Evidence with the use of transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) suggested that MNS is also present in the human brain [8]. Some studies sug‐ gest a similar learning effect of action observation and physical practice [9–11]. Caspers et al. reported the neural network of action observation using ALE meta‐analysis [12]. Brain regions showing consistent activation across action observation experiments were observed symmetrically across both hemispheres in frontal areas BA 44/45, lateral dorsal premotor cortex (dPMC, BA 6), supplementary motor area (SMA, BA 6), rostral IPL (area PFt), primary somatosensory cortex (SI, BA 1/2), SPL (area 7A), intraparietal cortex (IPS, area hIP3), posterior middle temporal gyrus (pMTG) at the transition to visual area V5, and the fusiform face area/fusiform body area (FFA/FBA). Both motor imagery and action observation share the activation of cortical neural networks as implicated in movement execution (**Figure 2**) [13]. Moreover, we reported that brain activity during movement observation, imagery, and execution uses different pathways according to the sensory modality (**Figure 3**) [14]. This chapter discusses the clinical results of motor imagery and action observation studies and rehabilitation applications.

frontal gyrus (MfG), supplementary motor area (SMA), and regions of the anterior insula were regions consistently activated during motor imagery. In the parietal lobes, the bilateral superior parietal lobule (SPL), supramarginal gyrus (SMG), and left inferior parietal lobule (IPL) and, in the subcortical regions, the left putamen, right thalamus, and pallidum were activated. Finally, the areas VI (bilateral) and the vermis of the cerebellum (CB) were also

**Figure 1.** Motor imagery and action observation [2]. Human brain activity during motor imagery (a) and action observation (b). (a) Brain areas activated during kinesthetic and visual motor imagery. The pattern of activity includes the following regions: ventral and dorsal part of the premotor cortex (PMC); the supplementary motor area (SMA); anterior cingulate cortex (aCC); superior parietal lobule (sPL) and inferior parietal lobule (IPL); precuneus; basal ganglia (BG); and cerebellum. (b) The complex brain network ("mirror neuron system") involved in action observation: the ventral premotor cortex (vPMC), posterior part of the inferior frontal gyrus (pIFG), rostral part of the inferior parietal

When a subject observes a specific action being performed, activation of the same neu‐ ral structures used for the movement pattern is also repeated in the subject (**Figure 1(b)**) [2]. The neurophysiological basis of action observation is represented by the discovery of mirror neurons in the cerebral cortex of monkeys [6, 7]. These neurons discharge dur‐ ing both the execution of goal‐directed actions and the observation of other individuals performing similar movements. The definition of the mirror neuron system (MNS) is the area that comprises the cerebral areas containing mirror neurons. Evidence with the use of transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) suggested that MNS is also present in the human brain [8]. Some studies sug‐ gest a similar learning effect of action observation and physical practice [9–11]. Caspers et al. reported the neural network of action observation using ALE meta‐analysis [12]. Brain regions showing consistent activation across action observation experiments were observed symmetrically across both hemispheres in frontal areas BA 44/45, lateral dorsal

found to be consistently activated.

14 Neurological Physical Therapy

lobule (rIPL), and posterior superior temporal sulcus (pSTS).

**Figure 2.** Outline of the overlap between executed, observed, and imagined reaching in the left dorsal premotor (superior frontal sulcus and gyrus) and left posterior parietal areas [13]. The overlaps in the premotor and parietal regions served as regions of interest in the percent signal change analysis. (a) Dorsal view of the left hemisphere. (b) Medial view of the left hemisphere. Executed, observed, and imagined reaching all activated a medial parietal area located in‐between the parieto‐occipital sulcus and the posterior end of the cingulate sulcus, outlined in light blue. Sup. frontal gyr., superior frontal gyrus; POS, parieto‐occipital sulcus; calcarine, calcarine sulcus; cingulate sulc., cingulate sulcus.

**Figure 3.** Brain activity during observation, imagery, and execution of tool use [14]. The top row of the images shows the left side of the brain, whereas the bottom row of the images shows the right side of the brain. (a) Brain regions where a significant increase in the oxyhemoglobin (oxyHb) levels was detected during (1) imagery and (2) execution of the chopsticks movement. No significant differences in the oxyHb levels were detected during observation of the chopsticks movement. (b) Brain regions where a significant increase in the oxyHb levels was detected during (1) observation, (2) imagery, and (3) execution of the hammer movement.

## **2. Clinical studies of motor imagery**

**Figure 3.** Brain activity during observation, imagery, and execution of tool use [14]. The top row of the images shows the left side of the brain, whereas the bottom row of the images shows the right side of the brain. (a) Brain regions where a significant increase in the oxyhemoglobin (oxyHb) levels was detected during (1) imagery and (2) execution of the chopsticks movement. No significant differences in the oxyHb levels were detected during observation of the chopsticks movement. (b) Brain regions where a significant increase in the oxyHb levels was detected during (1) observation, (2)

imagery, and (3) execution of the hammer movement.

16 Neurological Physical Therapy

Motor imagery studies were conducted on several diseases relating to the central nervous system and acute injuries involving orthopedics such as subacute stroke [15–19], chronic stroke [20–22], traumatic brain injury [23], multiple sclerosis [23], shoulder impingement syndrome [24], postsurgical anterior cruciate ligament [25], postsurgical flexor tendon repair [26], burn injury [27], phantom limb pain [28], complex regional pain syndrome [28, 29], and motor coordination problems [30]. **Table 1** lists motor imagery clinical studies found in PubMed. "Motor imagery" which did not include "Brain Computer Interface (BCI)" or "Brain Machine Interface (BMI)" was used as a finding keyword, and the searched article type was "Randomized Controlled Trial (RCT)."

Nearly all studies reported that the effectiveness of motor imagery in orthopedic diseases was significant. Hoyek et al. investigated the effect of motor imagery on a range of motion and pain in patients with stage II shoulder impingement syndrome [24] and found positive results in the intervention group compared to the control group. This indicates that motor imagery contributes to a range of motion improvements and pain reductions in patients with stage II shoulder impingement syndrome. Lebon et al. investigated the effect of motor imag‐ ery on muscle activity in patients with a postsurgical anterior cruciate ligament [25]. The results showed that the intervention group significantly improved compared to the control group, which states that motor imagery improves motor recovery in patients after anterior cruciate ligament surgery. Stenekes et al. examined the effect of motor imagery on hand func‐ tion during immobilization after flexor tendon repair [26]. The results showed that increased preparation time significantly reduced after the immobilization period in the intervention group compared with the control group. This study disclosed that motor imagery improves hand functions in patients after surgical flexor tendon repair.

The effectiveness of motor imagery in patients with pain is also significant. Moseley et al. investigated the effect of graded motor imagery on pain and swelling in patients with com‐ plex regional pain syndrome [24]. The results showed that the neuropathic pain scale and finger circumference both significantly improved after training in the intervention group com‐ pared to the control group. Moreover, the improvement was observed for 12 weeks. Another study by Moseley et al. indicated that a motor imagery program for patients with complex regional pain syndrome not displaying a limp was effective. Moseley et al. reported the effect of graded motor imagery on pain and disability in patients with phantom limb pain or com‐ plex regional pain syndrome, and the results indicated that pain and disability significantly improved through motor imagery after training in the intervention group compared with the control group. In addition, the effect of the training lasted for 6 months [28].

On the other hand, some studies indicate that motor imagery has both effective and ineffective results for motor recovery in stroke patients. The effects of motor imagery were observed in upper extremity function in subacute [16] and chronic [23] stroke patients, gait function in sub‐ acute [15, 18] and chronic [20–22] stroke patients, and balance functions in chronic stroke patients [22]. Motor imagery used for motor recovery showed a lack of results in subacute stroke patients with limited upper extremity function [19], stroke patients struggling with goal attainment and

Wellbeing VAS (−)

**References** Oostra et al. [15]

Hoyek et al. [24]

Dickstein et al. [20]

Sun et al. [21]

Mihara et al. [16]

Cho et al. [22]

Schuster et al. [17]

RCT

Patients with subacute

39

MI embedded into

2 weeks

physiotherapy vs MI

added to physiotherapy vs

physiotherapy

stroke

RCT

Patients with chronic

28

MI + gait training vs gait

6 weeks

training

stroke

RCT

Patients with subacute

20

Real‐neurofeedback with MI

2 weeks

FMA (+)

Action research arm test (−)

Motor activity log (−)

KVIQ‐10 (+)

Functional reach test (+)

Timed up‐and‐go test (+)

10‐m walk test (+)

FMA (+)

Motor task (time) (+)\*

Motor task (help) (+)\*

KVIQ visual (−)

KVIQ kinesthetic (−)

Imaprax visual (−)

Berg balance scale (−)

Activities‐specific balance

confidence scale (−)

Wellbeing VAS (−)

+ standard rehab vs sham‐

neurofeedback with MI +

standard rehab

stroke

RCT

Patients with severe

18

MI + standard rehab vs

4 weeks

FMA‐UE (+)

fMRI

standard rehab

chronic stroke

RCT

Patients with chronic

23

Integrated MI practice vs

4 weeks

upper extremity rehab

stroke

RCT

Patients with stage II

16

MI + standard rehab vs

4 weeks

standard rehab

shoulder impingement

syndrome

RCT

**Study design**

**Type of patients**

Patients with subacute

44

MI + standard rehab vs

6 weeks

muscle relaxation + standard

rehab

stroke

**N**

**Intervention**

**Treatment period**

**Outcome measures and results**

MIQ‐RS visual (−)

MIQ‐RS kinesthetic (+)

Imagery walking time/actual

18 Neurological Physical Therapy

walking time (−)

10‐m walk test (+)

FMA‐LE (−)\*

Constant score (+)

ROM (+)

Pain VAS (+)

10‐m walk test (+)

Community ambulation (steps) (−)

Community ambulation (maximal

activity) (−)

Falls efficacy scale (+)\*

**Table1.** Representative clinical studies of motor imagery.

Edition, FMA‐UE/LE, Fugl‐Meyer Assessment Upper Extremity/Lower Extremity; ROM, Range of Motion; VAS, Visual Analogue Scale, fMRI, functional Magnetic

Resonance Imaging; KVIQ, Kinesthetic and Visual Imagery Questionnaire; EMG, Electromyogram; NRS, Numerical Rating Scale.

task performance [17], and those with traumatic brain injury and multiple sclerosis [23]. A pos‐ sible reason for the different effects of motor imagery is the decline of cognitive function after a patient experiences a stroke. A previous study reported that not only motor function but also cognitive function declines after a stroke [31]. Moreover, cognitive function is largely associated with the ability to execute motor imagery [32]. Therefore, the cognitive function level in stroke patients influences the outcome of motor imagery training.

## **3. Clinical studies of action observation**

**References** Stenekes et al. [26]

Moseley et al. [28]

Moseley et al. [29]

Wilson et al. [30]

RCT

Children with motor

54

MI training vs Traditional

5 weeks

Perceptual‐Motor Training vs

No‐treatment

\*Significant within‐subject factor of time (*P* < 0.05) but no significant between‐subject factor of group or interaction time × group (*P* > 0.05).

RCT, Randomized Controlled Trial; CRPS1, Complex Regional Pain Syndrome type 1; MI, Motor Imagery; MIQ‐RS, Movement Imagery Questionnaire‐Revised, Second

Edition, FMA‐UE/LE, Fugl‐Meyer Assessment Upper Extremity/Lower Extremity; ROM, Range of Motion; VAS, Visual Analogue Scale, fMRI, functional Magnetic

Resonance Imaging; KVIQ, Kinesthetic and Visual Imagery Questionnaire; EMG, Electromyogram; NRS, Numerical Rating Scale.

**Table 1.**

Representative clinical studies of motor imagery.

coordination problems

RCT

RCT

Patients with phantom

51

Graded MI vs standard rehab

6 weeks

limb pain, CRPS1

Patients with chronic

13

Graded MI vs ongoing

6 weeks

medical management

CRPS1

RCT

**Study design**

**Type of patients**

Patients after surgical

28

MI + standard rehab vs

6 weeks

standard rehab

flexor tendon repair

**N**

**Intervention**

**Treatment period**

**Outcome measures and results**

Preparation time (+)

Michigan hand outcome

questionnaire score (−)

20 Neurological Physical Therapy

Hand function VAS (−)

Kinematic analysis (−)

Active total motion (−)

Grip strength (−)

Pain VAS (+)

Function NRS (+)

Neuropathic pain scale (+)

Finger circumference (+)

Total movement assessment battery

for children scores (+)\*

Clinical studies of action observation were also conducted on a wide range of diseases, such as central nervous system diseases and orthopedic events that include acute stroke [33], sub‐ acute stroke [34], chronic stroke [35], Parkinson's disease [36, 37], cerebral palsy [38], and orthopedic surgery [39]. **Table 2** lists clinical studies of action observations found in PubMed. "Action observation" was used as a finding keyword, and "Randomized Controlled Trial (RCT)" was the article type that was searched.

The first clinical study of action observation was reported by Ertelt et al. [35]. This study examined the effect of action observation therapy on motor recovery in chronic stroke patients using motor

\* Significant within‐subject factor of time (*P* < 0.05) but no significant between‐subject factor of group or interaction time × group (*P* > 0.05).

RCT, Randomized Controlled Trial; AO, Action Observation; FMA‐UE, Fugl‐Meyer Assessment Upper Extremity; BBT, Box and Block Test; FAT, Frenchay Arm Test; FIM, Functional Independence Measure; FOG, Freezing of Gait; fMRI, functional Magnetic Resonance Imaging.

**Table 2.** Representative clinical studies of action observation.

function outcome and functional magnetic resonance imaging (fMRI). The results showed that motor function after a four‐week training significantly improved. Moreover, the improvement was retained for 8 weeks post‐training. fMRI during the sensorimotor task of object manipula‐ tion showed that significant activations in the bilateral ventral premotor cortex (vPMC), bilateral superior temporal gyrus, supplementary motor area, and the contralateral supramarginal gyrus were observed in the intervention group compared to the control group. This study indicated that action observation has positive effects for motor recovery in stroke patients. Similarly, other studies reported that action observation is effective for motor recovery of upper extremity func‐ tion in acute stoke patients [33] and for the improvement of motor function in subacute stroke patients [34].

Action observation is also helpful in patients with Parkinson's disease. Pelosin et al. investigated the effect of action observation on gait‐freezing (GF) [37]. The results showed that the GF func‐ tional score after training significantly improved in both the intervention and control groups. In addition, retention was observed after the four‐week training period in only the intervention group. This study indicated that action observation had a positive effect on the walking ability in Parkinson's disease patients displaying GF. In the same manner, another study reported that action observation improved finger function in patients with Parkinson's disease [36].

Action observation is also a useful tool for postsurgical orthopedic patients. Bellelli et al. reported the effect of action observation treatment on motor function in patients who under‐ went hip arthroplasty, knee arthroplasty, and hip fracture repair [39]. The functional score after training was significantly higher in the intervention group than the control group. This revealed that action observation treatment is effective for postsurgical orthopedic patients.

These studies suggest that the effect of action observation is improved not only in central nervous system diseases but also in orthopedic diseases and events.

## **4. Application of motor imagery and action observation to physical therapy**

As described above, motor imagery and action observation have positive effects on central ner‐ vous system diseases, as well as in patients who experienced orthopedic diseases and events.

Kim and Lee reported the comparison of the effects of both action observation and motor imagery training on motor recovery of chronic stroke patients [40]. The results showed signifi‐ cant improvements in a timed up‐and‐go test, gait speed, cadence, and single limb support of the affected side in motor imagery and action observation groups after training. Although no significant difference was observed between action observation and motor imagery groups, the action observation group showed significant improvement compared with the control group. This study indicated that action observation had positive effects on dynamic balance and gait abilities compared with motor imagery.

The different effects between motor imagery and action observation are associated with the degree of difficulty in training methods. Specifically, action observation uses a bottom‐up approach based on sensory information. Human motor control has high dependence on visual information; therefore, as action observation uses the sense of vision, the level of dif‐ ficulty is lower compared with motor imagery. Additionally, action observation can influence human movement easily. On the other hand, motor imagery uses a top‐down approach based on cognitive information. The cognitive function is greatly associated with cognitive infor‐ mation processing. Therefore, the level of difficulty is higher in motor imagery than action observation, especially for stroke patients who see a decline in cognitive function [31]. How then are action observation and motor imagery used for physical therapy?

function outcome and functional magnetic resonance imaging (fMRI). The results showed that motor function after a four‐week training significantly improved. Moreover, the improvement was retained for 8 weeks post‐training. fMRI during the sensorimotor task of object manipula‐ tion showed that significant activations in the bilateral ventral premotor cortex (vPMC), bilateral superior temporal gyrus, supplementary motor area, and the contralateral supramarginal gyrus were observed in the intervention group compared to the control group. This study indicated that action observation has positive effects for motor recovery in stroke patients. Similarly, other studies reported that action observation is effective for motor recovery of upper extremity func‐ tion in acute stoke patients [33] and for the improvement of motor function in subacute stroke

**References Study design Type of patients N Intervention Treatment**

RCT Patients with

RCT Patients with

**Table 2.** Representative clinical studies of action observation.

chronic stroke

Parkinson's disease

**period**

20 AO + standard rehab vs landscape + standard rehab

16 AO + standard rehab vs sham‐AO + standard rehab

Significant within‐subject factor of time (*P* < 0.05) but no significant between‐subject factor of group or interaction

RCT, Randomized Controlled Trial; AO, Action Observation; FMA‐UE, Fugl‐Meyer Assessment Upper Extremity; BBT, Box and Block Test; FAT, Frenchay Arm Test; FIM, Functional Independence Measure; FOG, Freezing of Gait; fMRI,

**Outcome measures and results**

Number of FOG episodes

Number of FOG episodes (start walking) (+) Number of FOG episodes

Number of FOG episodes

Timed up and go test (+)\* 10‐meter walking test (+)\* Tinetti scale (part I) (+)\* Berg balance scale (+)\* Tinetti scale (part II) (+)\* 39‐item PD questionnaire (+)\*

Wolf motor function test (+) Stroke impact scale (+)

4 weeks FOG Questionnaire (+)\*

(total) (+)

(turn) (+)

fMRI (+)

4 weeks FAT (+)

(obstacle) (−)

Action observation is also helpful in patients with Parkinson's disease. Pelosin et al. investigated the effect of action observation on gait‐freezing (GF) [37]. The results showed that the GF func‐ tional score after training significantly improved in both the intervention and control groups. In addition, retention was observed after the four‐week training period in only the intervention group. This study indicated that action observation had a positive effect on the walking ability in Parkinson's disease patients displaying GF. In the same manner, another study reported that

action observation improved finger function in patients with Parkinson's disease [36].

patients [34].

Pelosin et al. [37]

22 Neurological Physical Therapy

Ertelt et al. [35]

time × group (*P* > 0.05).

functional Magnetic Resonance Imaging.

\*

Gatti et al. revealed that action observation is superior to motor imagery in the early stages of new complex motor learning, as shown by behavioral [41] and EEG data [42]. As described above, motor imagery is influenced by the environment, personal imaging ability, and mental effort. In contrast, action observation is easier to apply, despite activation of the same neural network as motor imagery [43]. In addition, Conson et al. revealed that action observation had an effect of promoting motor imagery [44]. According to these studies, it is recommended that strategies should transfer from action observation performed in the early stages of motor learning to motor imagery performed during the later stages of motor learning.

Graded motor imagery is a similar therapeutic approach that consists of three specific levels of increasing complexity in terms of time and difficulty, which is thought to reflect graded activation of cortical networks [45]. Graded motor imagery includes three consecutive steps: implicit motor imagery, explicit motor imagery, and mirror therapy [46]. Polli et al. investi‐ gated the feasibility and clinical effects of graded motor imagery in motor function recovery after a stroke [47]. The results showed that the Wolf Motor Function Test and Fugl‐Meyer Assessment after training in the intervention group significantly improved compared to the control group. This study demonstrated that graded motor imagery is a feasible treatment for stroke patients to provide better outcomes than conventional therapy.

Thus, gradually increasing the difficulty level of treatment strategy is recommended. However, motor imagery and action observation are just tools for modulating brain states [48]. Therefore, it is important to choose the appropriate treatment strategy according to functional character‐ istics and recovery phases of patients in the clinical setting [49].

## **Acknowledgements**

This work was supported by JSPS KAKENHI (Grant Number JP26750208) and ASTEM RI/ KYOTO.

## **Author details**

Hideki Nakano\* and Takayuki Kodama

\*Address all correspondence to<EMAIL_ADDRESS>
Department of Physical Therapy, Faculty of Health Science, Kyoto Tachibana University, Kyoto, Japan

## **References**

[5] Hétu S, Grégoire M, Saimpont A, Coll MP, Eugène F, Michon PE, Jackson PL. The neural network of motor imagery: An ALE meta‐analysis. Neurosci Biobehav Rev. 2013;37(5):930–49.

Graded motor imagery is a similar therapeutic approach that consists of three specific levels of increasing complexity in terms of time and difficulty, which is thought to reflect graded activation of cortical networks [45]. Graded motor imagery includes three consecutive steps: implicit motor imagery, explicit motor imagery, and mirror therapy [46]. Polli et al. investi‐ gated the feasibility and clinical effects of graded motor imagery in motor function recovery after a stroke [47]. The results showed that the Wolf Motor Function Test and Fugl‐Meyer Assessment after training in the intervention group significantly improved compared to the control group. This study demonstrated that graded motor imagery is a feasible treatment for

Thus, gradually increasing the difficulty level of treatment strategy is recommended. However, motor imagery and action observation are just tools for modulating brain states [48]. Therefore, it is important to choose the appropriate treatment strategy according to functional character‐

This work was supported by JSPS KAKENHI (Grant Number JP26750208) and ASTEM RI/

Department of Physical Therapy, Faculty of Health Science, Kyoto Tachibana University,

[1] Mulder T. Motor imagery and action observation: Cognitive tools for rehabilitation. J

[2] Abbruzzese G, Avanzino L, Marchese R, Pelosin E. Action observation and motor imag‐ ery: Innovative cognitive tools in the rehabilitation of Parkinson's disease. Parkinsons

[3] Gentili R, Han CE, Schweighofer N, Papaxanthis C. Motor learning without doing: Trial‐ by‐trial improvement in motor performance during mental training. J Neurophysiol.

[4] Gentili R, Papaxanthis C, Pozzo T. Improvement and generalization of arm motor per‐ formance through motor imagery practice. Neuroscience. 2006;137(3):761–72.

stroke patients to provide better outcomes than conventional therapy.

istics and recovery phases of patients in the clinical setting [49].

\*Address all correspondence to<EMAIL_ADDRESS>
Neural Transm (Vienna). 2007;114(10):1265–78.

**Acknowledgements**

24 Neurological Physical Therapy

KYOTO.

**Author details**

Kyoto, Japan

**References**

Dis. 2015;2015:1–9.

2010;104(2):774–83.

Hideki Nakano\* and Takayuki Kodama

[34] Sale P, Ceravolo MG, Franceschini M. Action observation therapy in the subacute phase promotes dexterity recovery in right‐hemisphere stroke patients. Biomed Res Int. 2014;2014:1–7.

[20] Dickstein R, Deutsch JE, Yoeli Y, Kafri M, Falash F, Dunsky A, Eshet A, Alexander N. Effects of integrated motor imagery practice on gait of individuals with chronic stroke: A half‐crossover randomized study. Arch Phys Med Rehabil. 2013;94(11):2119–25. [21] Sun L, Yin D, Zhu Y, Fan M, Zang L, Wu Y, Jia J, Bai Y, Zhu B, Hu Y. Cortical reorganiza‐ tion after motor imagery training in chronic stroke patients with severe motor impair‐

[22] Cho HY, Kim JS, Lee GC. Effects of motor imagery training on balance and gait abilities in post‐stroke patients: A randomized controlled trial. Clin Rehabil. 2013;27(8):675–80.

[23] Bovend'Eerdt TJ, Dawes H, Sackley C, Izadi H, Wade DT. An integrated motor imagery program to improve functional task performance in neurorehabilitation: A single‐blind

[24] Hoyek N, Di Rienzo F, Collet C, Hoyek F, Guillot A. The therapeutic role of motor imagery on the functional rehabilitation of a stage II shoulder impingement syndrome.

[25] Lebon F, Guillot A, Collet C. Increased muscle activation following motor imagery dur‐ ing the rehabilitation of the anterior cruciate ligament. Appl Psychophysiol Biofeedback.

[26] Stenekes MW, Geertzen JH, Nicolai JP, De Jong BM, Mulder T. Effects of motor imag‐ ery on hand function during immobilization after flexor tendon repair. Arch Phys Med

[27] Guillot A, Lebon F, Vernay M, Girbon JP, Doyon J, Collet C. Effect of motor imagery in

[28] Moseley GL. Graded motor imagery for pathologic pain: A randomized controlled trial.

[29] Moseley GL. Graded motor imagery is effective for long‐standing complex regional pain

[30] Wilson PH, Thomas PR, Maruff P. Motor imagery training ameliorates motor clumsiness

[31] Arsic S, Konstantinovic Lj, Eminovic F, Pavlovic D, Popovic MB, Arsic V. Correlation between the quality of attention and cognitive competence with motor action in stroke

[32] Munzert J, Lorey B, Zentgraf K. Cognitive motor processes: The role of motor imagery in

[33] Franceschini M, Ceravolo MG, Agosti M, Cavallini P, Bonassi S, Dall'Armi V, Massucci M, Schifini F, Sale P. Clinical relevance of action observation in upper‐limb stroke reha‐ bilitation: A possible role in recovery of functional dexterity. A randomized clinical trial.

the rehabilitation of burn patients.  Pain. 2004;108(1–2):192–8.

the study of motor representations. Brain Res Rev. 2009;60(2):306–26.

ment: A longitudinal fMRI study. Neuroradiology. 2013;55(7):913–25.

randomized controlled trial. Arch Phys Med Rehabil. 2010;91(6):939–46.

Disabil Rehabil. 2014;36(13):1113–9.

2012;37(1):45–51.

26 Neurological Physical Therapy

Rehabil. 2009;90(4):553–9.

Neurology. 2006;67(12):2129–34.

in children. J Child Neurol. 2002;17(7):491–8.

patients. Biomed Res Int. 2015;2015:823136.

Neurorehabil Neural Repair. 2012;26(5):456–62.

**Chapter 3**

## **The Effect of Motor Imagery on Spinal Motor Neuron Excitability and Its Clinical Use in Physical Therapy**

Yoshibumi Bunno, Yuki Fukumoto,

Todo Marina and Chieko Onigata

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67471

#### Abstract

[48] Vogt S, Di Rienzo F, Collet C, Collins A, Guillot A. Multiple roles of motor imagery dur‐

[49] Hatem SM, Saussez G, Della Faille M, Prist V, Zhang X, Dispa D, Bleyenheuft Y. Rehabilitation of motor function after stroke: A multiple systematic review focused on techniques to stimulate upper extremity recovery. Front Hum Neurosci. 2016;10:442.

ing action observation. Front Hum Neurosci. 2013;7:807.

28 Neurological Physical Therapy

We investigated the influence of the imagined muscle contraction strengths on spinal motor neuron excitability in healthy volunteers. F-wave was used for assessing spinal motor excitability. The F-waves during motor imagery (MI) under 10, 30, 50, 70, and 100% maximal voluntary contractions (MVCs) were compared. Furthermore, we investigated changes of the F-waves during motor imagery for 5min. Motor imagery under 10, 30, 50, 70, and 100% maximal voluntary contractions can increase spinal motor neuron excitability. However, the imagined muscle contraction strengths were not involved in changes of spinal motor neuron excitability. Additionally, spinal motor neuron excitability after 5min from onset of motor imagery returned to the rest level. Thus, in clinical use of motor imagery, slightly imagined muscle contraction strength is enough for facilitating spinal motor neuron excitability. Also, duration of motor imagery needs to be considered.

Keywords: motor imagery, F-wave, imagined muscle contraction strength, duration, physical therapy

## 1. Introduction

Motor imagery (MI) is defined as a cognitive process in which the subjects imagine that they perform movements without actually performing movements and muscle contractions [1].

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

MI has been shown to improve various motor functions in healthy subjects. Specifically, Yue and Cole [2] suggested that MI of little finger abduction under maximal voluntary contraction (MVC) for 4weeks could increase muscle strength. Additionally, MI of ankle dorsiflexion under MVC for 4weeks could increase muscle strength [3]. Also, Guillot et al. [4] suggested that muscle flexibility was improved after MI of stretching for 5weeks. Furthermore, in clinical settings, MI can be applied in physical therapy for patients with damage to the central nervous system, such as stroke, Parkinson's disease, and spinal cord injury.

The effects of MI have been discussed in numerous neurophysiological studies. Various brain activities, including primary motor area, supplementary motor area, premotor area, somatosensory area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia, were activated during MI by using positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and near infrared spectroscopy (NIRS) [5–8]. These regions were also activated in motor execution. Thus, MI and motor execution are considered to share common neural networks. Furthermore, enhanced corticospinal excitability may explain the increase in motor evoked potentials (MEPs) amplitude by applying transcranial magnetic stimulation (TMS) over the primary motor area during MI [9]. These previous studies suggested that MI can facilitate the central nervous system.

However, other studies could not show the certain results in spinal motor neuron excitability during MI by using the F-wave, H-reflex, and T-reflex. The F-wave, H-reflex, and T-reflex are considered as indices of spinal motor neuron excitability. We previously studied spinal motor neuron excitability during MI of isometric thenar muscle activity. The persistence and F/M amplitude ratio during MI of thenar muscle activity under 50% MVC were significantly increased compared to that at rest [10]. Taniguchi et al. [11] reported that the F/M amplitude ratio after volitional relaxation for 3h was significantly decreased. When subjects did volitional relaxation and MI of thumb abduction simultaneously, the F/M amplitude ratio was maintained at that before volitional relaxation level. This indicated that MI can increase spinal motor neuron excitability. Whereas Kasai et al. [9] reported that the H-reflex amplitude was not changed during MI of wrist flexion movement, Oishi et al. [12] reported that there are various results in the H-reflex amplitude during MI in speed skaters. Thus, it might be suggested that spinal motor neuron excitability was not always increased during MI, although MI can increase the central nervous system.

Our final goal is to find the way that MI obtained the most beneficial effect. To assess spinal motor neuron excitability is as important as the central nervous system, because we think that facilitation of spinal motor neuron excitability is required for improvement of motor function. Thus, in this chapter, we would like to introduce our previous work about spinal motor neuron excitability during MI under various MI conditions. First, we described spinal motor neuron excitability during MI under various imagined muscle contraction strengths. Next, we described the influence of duration of MI on spinal motor neuron excitability. Additionally, at the end of the chapter, we discuss how to apply MI to physical therapy.

## 2. Spinal motor neuron excitability of MI under various imagined muscle contractions

#### 2.1. Spinal motor neuron excitability of MI under 10, 30, 50, and 70% MVC

#### 2.1.1. Purpose

MI has been shown to improve various motor functions in healthy subjects. Specifically, Yue and Cole [2] suggested that MI of little finger abduction under maximal voluntary contraction (MVC) for 4weeks could increase muscle strength. Additionally, MI of ankle dorsiflexion under MVC for 4weeks could increase muscle strength [3]. Also, Guillot et al. [4] suggested that muscle flexibility was improved after MI of stretching for 5weeks. Furthermore, in clinical settings, MI can be applied in physical therapy for patients with damage to the central nervous system, such as stroke, Parkinson's disease, and spinal cord

The effects of MI have been discussed in numerous neurophysiological studies. Various brain activities, including primary motor area, supplementary motor area, premotor area, somatosensory area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia, were activated during MI by using positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and near infrared spectroscopy (NIRS) [5–8]. These regions were also activated in motor execution. Thus, MI and motor execution are considered to share common neural networks. Furthermore, enhanced corticospinal excitability may explain the increase in motor evoked potentials (MEPs) amplitude by applying transcranial magnetic stimulation (TMS) over the primary motor area during MI [9]. These previous studies

However, other studies could not show the certain results in spinal motor neuron excitability during MI by using the F-wave, H-reflex, and T-reflex. The F-wave, H-reflex, and T-reflex are considered as indices of spinal motor neuron excitability. We previously studied spinal motor neuron excitability during MI of isometric thenar muscle activity. The persistence and F/M amplitude ratio during MI of thenar muscle activity under 50% MVC were significantly increased compared to that at rest [10]. Taniguchi et al. [11] reported that the F/M amplitude ratio after volitional relaxation for 3h was significantly decreased. When subjects did volitional relaxation and MI of thumb abduction simultaneously, the F/M amplitude ratio was maintained at that before volitional relaxation level. This indicated that MI can increase spinal motor neuron excitability. Whereas Kasai et al. [9] reported that the H-reflex amplitude was not changed during MI of wrist flexion movement, Oishi et al. [12] reported that there are various results in the H-reflex amplitude during MI in speed skaters. Thus, it might be suggested that spinal motor neuron excitability was not always increased during MI, although MI can increase the central

Our final goal is to find the way that MI obtained the most beneficial effect. To assess spinal motor neuron excitability is as important as the central nervous system, because we think that facilitation of spinal motor neuron excitability is required for improvement of motor function. Thus, in this chapter, we would like to introduce our previous work about spinal motor neuron excitability during MI under various MI conditions. First, we described spinal motor neuron excitability during MI under various imagined muscle contraction strengths. Next, we described the influence of duration of MI on spinal motor neuron excitability. Additionally, at the end of the chapter, we discuss how to apply MI to

suggested that MI can facilitate the central nervous system.

injury.

30 Neurological Physical Therapy

nervous system.

physical therapy.

We previously reported that spinal motor neuron excitability during MI of isometric thenar muscle activity under 50% MVC was significantly increased in comparison with that at rest [10]. In actual motion, Suzuki et al. [15] compared spinal motor neuron excitability during actual isometric thenar muscle activity under 25, 50, 75, and 100% MVC. The persistence and F/M amplitude ratio increased linearly with the muscle contraction strength. Spinal motor neuron excitability during MI increases linearly with the imagined muscle contraction strength if MI and motor execution share common neural networks. However, it was unclear whether the imagined muscle contraction strength affects the changes of spinal motor neuron excitability. Then, we investigated changes of spinal motor neuron excitability during MI of isometric thenar muscle activity under various imagined muscle contraction strengths. Specifically, we used 10, 30, 50, and 70% MVC for the imagined muscle contraction strength. In addition, we assessed spinal motor neuron excitability by using F-wave.

#### 2.1.2. Materials

We included 10 healthy volunteers (5 males and 5 females; mean age, 28.74.5years. All subjects provided informed consent prior to the study's commencement. This study was approved by the Research Ethics Committee at Kansai University of Health Sciences. The experiments were conducted in accordance with the Declaration of Helsinki.

#### 2.1.3. Methods

Subjects were in a supine position with muscles relaxed and instructed to fix one eye on a pinch meter monitor [digital indicator F304A (unipulse)] throughout the test (Figure 1). Abrasive gel was applied to keep the skin impedance below 5kΩ. The temperature was maintained at 25C. A Viking Quest electromyography (EMG) machine (Natus Medical Inc., Pleasanton, USA) was used for F-wave recording (Figure 1). We recorded F-waves from the left thenar muscles after stimulating the left median nerve. A pair of disks was attached with collodion to the skin over the belly and the bones of the metacarpophalangeal joint of the thumb. The stimulating electrodes comprised the cathode placed over the left median nerve 3cm proximal to the palmar crease, and the anode was placed 2cm more proximally (Figure 2). The maximal stimulus was determined by delivering 0.2-ms square-wave pulses of increasing intensity to elicit the largest compound muscle action potential (M-wave). The supramaximal stimuli (adjusted up to 20% higher than the maximum stimulus intensity) were delivered at 0.5Hz. The bandwidth filter ranged from 2Hz to 3kHz.

We showed the typical F-wave forms from thenar muscle after applying 30 electrical stimuli on the median nerve (Figure 3).

Figure 1. The F-wave recording instruments.

Figure 2. The F-wave recording condition.

In the resting trial (rest), the F-waves were recorded during relaxation. Next, we measured MVC by asking the subjects to apply maximum pressure to the pinch meter sensor between left thumb and index finger for 10s. Subsequently, the subjects were required to learn isometric thenar muscle activity under 10% MVC for 1min. The subjects were instructed to keep the 10% MVC value, which was displayed on the digital pinch meter monitor. For MI trial, the subjects were instructed to imagine 10% MVC thenar muscle activity while holding the sensor between their thumb and index finger without exerting any muscle contractions. F-waves were measured both during (10% MI) and immediately after 10% MI (post). The above process was defined as the MI using a 10% MVC condition (10% MI condition). This training process was repeated for MI of 30, 50, and 70% of MVC, and F-waves were recorded as described. Trials under these conditions were performed randomly on different days.

The Effect of Motor Imagery on Spinal Motor Neuron Excitability and Its Clinical Use in Physical Therapy http://dx.doi.org/10.5772/67471 33

Figure 3. The typical F-wave forms.

#### 2.1.4. Date analysis

The F-waves result from backfiring of spinal anterior horn neurons following distal antidromic electrical stimulation of α-motor neurons [16–18], in this case the median nerve. The F-waves from 30 stimuli were analyzed with respect to persistence, F/M amplitude ratio, and latency. Persistence was defined as the number of measurable F-wave responses divided by 30 supramaximal stimuli. The F/M amplitude ratio was defined as the mean amplitude of all responses divided by M-wave amplitude. Latency was defined as the mean latency from the time of stimulation to onset of measurable F-waves. Persistence reflects the number of backfiring anterior horn cells [17, 18]. The F/M amplitude ratio reflects the number of backfiring anterior horn cells and the excitability of individual cells [17, 18]. Therefore, these parameters are considered to be the indexes of spinal motor neuron excitability.

#### 2.1.5. Statistical analysis

In the resting trial (rest), the F-waves were recorded during relaxation. Next, we measured MVC by asking the subjects to apply maximum pressure to the pinch meter sensor between left thumb and index finger for 10s. Subsequently, the subjects were required to learn isometric thenar muscle activity under 10% MVC for 1min. The subjects were instructed to keep the 10% MVC value, which was displayed on the digital pinch meter monitor. For MI trial, the subjects were instructed to imagine 10% MVC thenar muscle activity while holding the sensor between their thumb and index finger without exerting any muscle contractions. F-waves were measured both during (10% MI) and immediately after 10% MI (post). The above process was defined as the MI using a 10% MVC condition (10% MI condition). This training process was repeated for MI of 30, 50, and 70% of MVC, and F-waves were recorded as described. Trials

under these conditions were performed randomly on different days.

Figure 2. The F-wave recording condition.

Figure 1. The F-wave recording instruments.

32 Neurological Physical Therapy

The normality of F-wave data was confirmed using the Kolmogorov-Smirnov and Shapiro-Wilk tests. The persistence, F/M amplitude ratio, and latency among three trials (rest, MI, post) under each MI condition (10% MI, 30% MI, 50% MI, and 70% MI conditions) were compared using the Friedman test and Scheffe's post hoc test. The relative values among the four MI conditions were compared using the Friedman test. We used IBM SPSS statistics ver.19 for all statistical analysis.

#### 2.1.6. Results

Persistence during MI under the four MI conditions was significantly increased compared to that at rest (Scheffe's test; 10% MI vs rest, 70% MI vs rest, \*\*p<0.01; 30% MI vs rest, 50% MI vs rest, \*p<0.05; Figures 4–7). Persistence immediately after MI was significantly decreased compared with that at MI (Scheffe's test; 10% MI vs post, 30% MI vs post, 70% MI vs post, \*p<0.05; Figures 4, 5, and 7). Persistence at post tended to be decreased compared with that at 50% MI (Scheffe's test; p=0.067; Figure 6).

Figure 4. The F-waves at rest, MI, and post trials under the 10% MI condition.

Figure 5. The F-waves at rest, MI, and post trials under the 30% MI condition.

Figure 6. The F-waves at rest, MI, and post trials under 50% MI condition.

The F/M amplitude ratio during MI under the three MI conditions was significantly increased compared to that at rest (Scheffe's test; 10% MI vs rest, 50% MI vs rest, \*\*p<0.01; 30% MI vs rest, \*p<0.05; Figures 4–6). The F/M amplitude ratio during 70% MI tended to be increased compared to that at rest (Scheffe's test; p=0.082; Figure 7). The F/M amplitude ratio immediately after 50% MI was significantly decreased compared to that at 50% MI (Scheffe's test; \*p<0.05; Figure 6).

Alternatively, no significant differences in latency were observed among three trials (rest, MI, and post) under the four MI conditions (Figures 4–7).

The relative values of persistence, F/M amplitude ratio, and latency did not exhibit significant differences among the four MI conditions (Figures 8–10).

Figure 7. The F-waves at rest, MI, and post trials under 70% MI condition.

2.1.6. Results

34 Neurological Physical Therapy

(Scheffe's test; p=0.067; Figure 6).

Figure 4. The F-waves at rest, MI, and post trials under the 10% MI condition.

Figure 5. The F-waves at rest, MI, and post trials under the 30% MI condition.

Figure 6. The F-waves at rest, MI, and post trials under 50% MI condition.

Persistence during MI under the four MI conditions was significantly increased compared to that at rest (Scheffe's test; 10% MI vs rest, 70% MI vs rest, \*\*p<0.01; 30% MI vs rest, 50% MI vs rest, \*p<0.05; Figures 4–7). Persistence immediately after MI was significantly decreased compared with that at MI (Scheffe's test; 10% MI vs post, 30% MI vs post, 70% MI vs post, \*p<0.05; Figures 4, 5, and 7). Persistence at post tended to be decreased compared with that at 50% MI

Figure 8. Comparison of relative values of persistence among the four MI conditions.

Figure 9. Comparison of relative values of F/M amplitude ratio among the four MI conditions.

Figure 10. Comparison of relative values of latency among the four MI conditions.

#### 2.2. Spinal motor neuron excitability during MI under 50 and 100% MVC

#### 2.2.1. Purpose

In previous work, MI under 10, 30, 50, and 70% MVC was shown to increase spinal motor neuron excitability [13, 14]. The imagined muscle contraction strengths did not influence the facilitation amount of spinal motor neuron excitability [13, 14]. However, Cowley et al. [20] suggested that the H-reflex amplitude during MI of plantar flexion under 100% MVC was significantly higher than that under 50% MVC. Therefore, we hypothesized that the MI of thenar muscle activity under 100% MVC will be higher than that under 50% MVC. In this study, we investigated spinal motor neuron excitability during MI under 50 and 100% MVC.

#### 2.2.2. Materials

We included 15 healthy subjects (13 males; 2 females; mean age, 25.35.04years). All subjects provided informed consent prior to the study's commencement. This study was approved by the Research Ethics Committee at Graduate School of Kansai University of Health Sciences. The experiments were conducted in accordance with the Declaration of Helsinki.

#### 2.2.3. Methods

The environment and conditions of the F-wave recording are the same as in previous work. The protocol of this study is as follows. In the resting trial (rest), the F-waves were recorded during relaxation. Next, we measured 100% MVC; that is, the subjects held the sensor of the pinch meter while exerting their maximum effort for 10s. Subsequently, the subjects were instructed to learn the isometric thenar muscle activity under 100% MVC for 1min as a motor task. They performed the activity using visual feedback while watching the digital monitor of the pinch meter. They were then instructed to perform MI of learned thenar muscle activity under 100% MVC by holding the sensor between the thumb and index finger. F-waves were recorded during the MI (100% MI). F-waves were recorded immediately after 100% MI trial (post). We defined the above process as the MI using the 100% MVC condition (100% MI condition). With regard to the MI using the 50% MVC condition (50% MI condition), F-waves were recorded using the same process. These conditions were randomly performed on different days.

#### 2.2.4. Statistical analysis

For statistical analysis, the normality of F-wave data was confirmed using the Kolmogorov-Smirnov and Shapiro-Wilk tests. Persistence, F/M amplitude ratio, and latency among three trials (rest, MI, and post) under each MVC MI condition were compared using the Friedman test and Scheffe's post hoc test. We also evaluated the relative values obtained under the two MI conditions by dividing the values of persistence, F/M amplitude ratio, and latency at rest with those obtained during MI at post. The relative values between the two MI conditions were compared using the Wilcoxon signed rank test. The significance level was set at p< 0.05. We used IBM SPSS statistics ver.19 for statistical analysis.

#### 2.2.5. Results

2.2. Spinal motor neuron excitability during MI under 50 and 100% MVC

Figure 9. Comparison of relative values of F/M amplitude ratio among the four MI conditions.

Figure 10. Comparison of relative values of latency among the four MI conditions.

In previous work, MI under 10, 30, 50, and 70% MVC was shown to increase spinal motor neuron excitability [13, 14]. The imagined muscle contraction strengths did not influence the facilitation amount of spinal motor neuron excitability [13, 14]. However, Cowley et al. [20] suggested that the H-reflex amplitude during MI of plantar flexion under 100% MVC was significantly higher than that under 50% MVC. Therefore, we hypothesized that the MI of thenar muscle activity under 100% MVC will be higher than that under 50% MVC. In this study, we investigated spinal motor neuron excitability during MI under 50 and 100% MVC.

We included 15 healthy subjects (13 males; 2 females; mean age, 25.35.04years). All subjects provided informed consent prior to the study's commencement. This study was approved by the Research Ethics Committee at Graduate School of Kansai University of Health Sciences.

The experiments were conducted in accordance with the Declaration of Helsinki.

2.2.1. Purpose

36 Neurological Physical Therapy

2.2.2. Materials

Persistence during MI under the two MI conditions was significantly increased compared with that at rest (Scheffe's test; \*\*p<0.01; Figures 11 and 12). Persistence immediately after MI (at post) under the two MI conditions did not show significant differences compared with that at rest (Figures 11 and 12). No significant differences were observed between the relative values of persistence obtained under the two MI conditions (Figure 13).

Figure 11. Changes in the F-wave under 50% MI condition.

Figure 12. Changes in the F-wave under 100% MI condition.

Figure 13. Comparison of relative values of persistence between 50 and 100% MI condition.

The F/M amplitude ratio during MI under the two MI conditions was significantly increased compared with that at rest (Scheffe's test; \*\*p<0.01; Figures 11 and 12). The F/M amplitude ratio immediately after MI (at post) under the two MI conditions did not show a significant difference compared with that at rest (Figures 11 and 12). No significant differences were observed between the relative values of F/M amplitude ratio obtained under the two MI conditions (Figure 14).

There were no significant differences in latency among three trials (rest, MI, post) under the two conditions (Figures 11 and 12). No significant differences were observed between the relative values of latency obtained under the two MI conditions (Figure 15).

The Effect of Motor Imagery on Spinal Motor Neuron Excitability and Its Clinical Use in Physical Therapy http://dx.doi.org/10.5772/67471 39

Figure 14. Comparison of relative values of F/M amplitude ratio between 50 and 100% MI condition.

Figure 15. Comparison of relative values of latency between 50 and 100% MI condition.

The F/M amplitude ratio during MI under the two MI conditions was significantly increased compared with that at rest (Scheffe's test; \*\*p<0.01; Figures 11 and 12). The F/M amplitude ratio immediately after MI (at post) under the two MI conditions did not show a significant difference compared with that at rest (Figures 11 and 12). No significant differences were observed between the relative values of F/M amplitude ratio obtained under the two MI

There were no significant differences in latency among three trials (rest, MI, post) under the two conditions (Figures 11 and 12). No significant differences were observed between the

relative values of latency obtained under the two MI conditions (Figure 15).

Figure 13. Comparison of relative values of persistence between 50 and 100% MI condition.

Figure 12. Changes in the F-wave under 100% MI condition.

38 Neurological Physical Therapy

conditions (Figure 14).

#### 2.3. Discussion

#### 2.3.1. Spinal motor neuron excitability during MI of thenar muscle activity

Summarizing the previous work, MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC can increase spinal motor neuron excitability. However, excitability does not vary with the imagined muscle contraction strengths.

Concerning the increase of spinal motor neuron excitability during MI, it was considered to influence the descending pathways corresponding to the thenar muscle. The previous studies have demonstrated that the activation of multiple cortical and subcortical regions contributes to motor preparation and planning during MI [5–8]. The activities of multiple brain regions as motor preparation and planning plausibly increased spinal motor neuron excitability via the corticospinal and/or extrapyramidal tract. Furthermore, MI is the mental rehearsal of a movement without any overt movement and muscle contraction [1]. Therefore, it is considered that motor inhibiting function was participated in simultaneously with motor preparation and planning. The supplementary motor area and premotor area are known to have functions of motor planning and inhibition in the GO/NO-GO task [21, 22]. Thus, spinal motor neuron excitability during MI may be generated by various functions (i.e., motor planning, preparation, and inhibition). In summary, it is plausible that the activation of multiple brain regions contributes to motor planning, preparation, and inhibition during MI increased spinal motor neuron excitability via the corticospinal and/or extrapyramidal tract.

Additionally, participants in all previous studies were instructed to perform MI while holding the sensor of a pinch meter. Therefore, the influence of haptic and proprioceptive perceptions during MI while holding the sensor on spinal motor neuron excitability should be considered. Mizuguchi et al. [23] reported that the MEP amplitude during MI was larger when a ball was squeezed than when no ball was held. Suzuki et al. [10] analyzed the changes in spinal motor neuron excitability between with and without holding the sensor MI tasks. The F-waves during MI while holding the sensor were greatly facilitated than without holding the sensor. The haptic and proprioceptive perceptions also contribute to the increase in spinal motor neuron excitability together with MI-activated pathways.

#### 2.3.2. The changes of spinal motor neuron excitability during MI under different imagined muscle contraction strengths

Our previous results suggested that the facilitation amount of spinal motor neuron excitability during MI under various imagined muscle contraction strengths (i.e., 10, 30, 50, 70, and 100% MVC) was similar. There are several previous studies investigating the changes of spinal motor neuron excitability of MI under different imagined muscle contraction strengths. Hale et al. [24] reported that the soleus H-reflex amplitude was significantly increased during MI of ankle plantar flexion under 20, 40, 60, 80, and 100% MVC than that at rest. However, no significant differences were observed in changes of the soleus H-reflex amplitude among five MI conditions. Bonnet et al. [25] reported that the soleus H-reflex amplitude was significantly increased during MI of ankle plantar flexion under 2 and 10% than that at rest. Additionally, there were no significant differences in changes of the soleus H-reflex amplitude between 2 and 10% MI condition. Similarly, Aoyama and Kaneko [26] reported that there were no differences in changes of the soleus H-reflex amplitude ratio between 50 and 100% MVC MI condition, although the H-reflex amplitude was increased during MI under two imagined muscle contraction strengths. In actual movement, spinal motor neuron excitability was increased linearly with muscle contraction strengths [15]. However, higher imagined muscle contraction strengths did not progressively enhance spinal motor neuron excitability. Concerning these results, also, one possibility is the contribution of a neural mechanism that inhibits actual movement and muscle contraction during MI. Park and Li [27] reported that the MEPs amplitude during MI of finger flexion or extension under 10, 20, 30, 40, 50, and 60% MVC was significantly higher than that at rest. However, there were no significant differences in changes of the MEPs amplitude among all MI conditions. Similarly, an event-related potential study found that the magnitude of primary motor cortex activity during MI did not correlate with the imagined contraction strengths but supplementary motor area and premotor area activities during MI did [28]. As mentioned above, supplementary motor area and premotor area have crucial roles in larger force generation [29], motor planning, preparation, and motor inhibition [21, 22]. Therefore, the supplementary motor area and premotor area may inhibit the actual muscle activity depending on the muscle contraction strength. These inputs from the supplementary motor area and premotor area may suppress any additional excitability conferred by MI with high imagined contraction strength. Furthermore, spinal motor neuron excitability during MI is thought to be affected by the central nervous system via the corticospinal and extrapyramidal tract. Thus, the degree of the changes of spinal motor neuron excitability during MI under different imagined muscle contraction strengths may be modulated by both excitatory and inhibitory inputs from the central nervous system.

MI ability is a factor that affects spinal motor neuron excitability. Lorey et al. [30] studied the relationship between activation of the cerebral cortex during MI and the vividness of MI by fMRI. The primary motor cortex, premotor area, primary somatosensory area, inferior parietal lobe and superior parietal lobe, putamen, and cerebellum showed activation during MI. In particular, activation of the premotor area, parietal lobule, and cerebellum was associated with increased vividness of MI, suggesting a correlation between the activation of the cerebral cortex and vividness of the MI. Therefore, MI ability may be a possible factor that affects spinal motor neuron excitability.

However, Bonnet et al. [25] reported that the T-reflex amplitude during MI under 10% MVC was significantly higher than that under 2% MVC. Additionally, Cowley et al. [20] reported that the soleus H-reflex amplitude ratio during MI under 100% MVC was significantly higher than that under 50% MVC. To clarify the reason why these results differed from our previous results, further research will be required.

#### 2.4. Conclusion

2.3. Discussion

40 Neurological Physical Therapy

2.3.1. Spinal motor neuron excitability during MI of thenar muscle activity

neuron excitability via the corticospinal and/or extrapyramidal tract.

neuron excitability together with MI-activated pathways.

contraction strengths

vary with the imagined muscle contraction strengths.

Summarizing the previous work, MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC can increase spinal motor neuron excitability. However, excitability does not

Concerning the increase of spinal motor neuron excitability during MI, it was considered to influence the descending pathways corresponding to the thenar muscle. The previous studies have demonstrated that the activation of multiple cortical and subcortical regions contributes to motor preparation and planning during MI [5–8]. The activities of multiple brain regions as motor preparation and planning plausibly increased spinal motor neuron excitability via the corticospinal and/or extrapyramidal tract. Furthermore, MI is the mental rehearsal of a movement without any overt movement and muscle contraction [1]. Therefore, it is considered that motor inhibiting function was participated in simultaneously with motor preparation and planning. The supplementary motor area and premotor area are known to have functions of motor planning and inhibition in the GO/NO-GO task [21, 22]. Thus, spinal motor neuron excitability during MI may be generated by various functions (i.e., motor planning, preparation, and inhibition). In summary, it is plausible that the activation of multiple brain regions contributes to motor planning, preparation, and inhibition during MI increased spinal motor

Additionally, participants in all previous studies were instructed to perform MI while holding the sensor of a pinch meter. Therefore, the influence of haptic and proprioceptive perceptions during MI while holding the sensor on spinal motor neuron excitability should be considered. Mizuguchi et al. [23] reported that the MEP amplitude during MI was larger when a ball was squeezed than when no ball was held. Suzuki et al. [10] analyzed the changes in spinal motor neuron excitability between with and without holding the sensor MI tasks. The F-waves during MI while holding the sensor were greatly facilitated than without holding the sensor. The haptic and proprioceptive perceptions also contribute to the increase in spinal motor

2.3.2. The changes of spinal motor neuron excitability during MI under different imagined muscle

Our previous results suggested that the facilitation amount of spinal motor neuron excitability during MI under various imagined muscle contraction strengths (i.e., 10, 30, 50, 70, and 100% MVC) was similar. There are several previous studies investigating the changes of spinal motor neuron excitability of MI under different imagined muscle contraction strengths. Hale et al. [24] reported that the soleus H-reflex amplitude was significantly increased during MI of ankle plantar flexion under 20, 40, 60, 80, and 100% MVC than that at rest. However, no significant differences were observed in changes of the soleus H-reflex amplitude among five MI conditions. Bonnet et al. [25] reported that the soleus H-reflex amplitude was significantly increased during MI of ankle plantar flexion under 2 and 10% than that at rest. Additionally, there were no significant differences in changes of the soleus H-reflex amplitude between 2

We investigated spinal motor neuron excitability during MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC [13, 14, 19]. As a result, MI of isometric thenar muscle activity can facilitate spinal motor neuron excitability. However, the imagined muscle contraction strengths were not involved in the changes of spinal motor neuron excitability.

## 3. Whether duration of MI affects spinal motor neuron excitability?

#### 3.1. Purpose

Our previous work suggested that MI can increase spinal motor neuron excitability, and differences in the imagined muscle contraction strengths are not involved in changes of spinal motor neuron excitability. Therefore, the previous results implied that MI of isometric thenar muscle activity under slight MVC (i.e., 10% MVC) can substantially facilitate spinal motor neuron excitability. Described in the introduction, one of our final goals is to find the way that MI obtained the most beneficial effect. Hale et al. [24] suggested that spinal motor neuron excitability was gradually increased with the number of MI trials. Gentili et al. [31] proposed that a number of MI trials are necessary to improve motor performance. To obtain a more beneficial effect of MI, the number of MI practices is considered to be important. On the other hand, in the optimal duration of MI that can facilitate motor performance, the most is unclear. Previous research used various durations of MI session, which ranged from a few seconds to approximately 200min (for review, see Driskell et al. [32]). A meta-analysis by Driskell et al. [32] suggested that a longer MI session does not always provide a beneficial effect on sports performance. Furthermore, they recommended approximately 20min to achieve a more beneficial effect. Hinshaw [33] also suggested that MI for 10–15min was considered to elicit the largest effect on performance, and Twining [34] indicated that 5min is the temporal limitation when we can concentrate and perform MI. Alternatively, the influence of duration of MI on the changes of spinal motor neuron excitability is not apparent. In our previous work [10, 13, 14, 19], participants were asked to perform MI for 1min. Thus, this research aimed to investigate the influence of MI for 5min on spinal motor neuron excitability by analyzing F-waves.

#### 3.2. Materials

We included 10 healthy volunteers (8 males; 2 females; mean age, 25.35.0years). All participants gave their written informed consent prior to the study's commencement. This study was approved by the Research Ethics Committee at Graduate School of Kansai University of Health Sciences. The experiment was conducted in accordance with the Declaration of Helsinki.

#### 3.3. Methods

The environment and conditions of the F-wave recording are the same as those for previous work. The protocol of this study is as follows. For the resting trial (rest), the F-waves were recorded while the muscle was relaxed. For the MI trial, participants first learned how to perform isometric thenar muscle activity under 50% MVC as a motor task for 1min. They were then instructed to imagine the isometric thenar muscle activity under 50% MVC by holding the sensor between the thumb and index finger for 5min. The F-waves were recorded at 1, 3, and 5 min after the onset of motor imagery (1min MI, 3min MI, and 5min MI, respectively). Immediately after MI, the F-waves were recorded (post).

#### 3.4. Statistical analysis

For statistical analysis, first, the normality of F-wave data was confirmed using the Shapiro-Wilk tests. Persistence, F/M amplitude ratio, and latency among five trials (rest, 1min MI, 3min MI, 5min MI, and post, respectively) were compared using the Friedman test and Scheffe's post hoc test. The significance level was set at p<0.05. We used IBM SPSS statistics ver.19 for statistical analysis.

#### 3.5. Results

3. Whether duration of MI affects spinal motor neuron excitability?

of MI for 5min on spinal motor neuron excitability by analyzing F-waves.

diately after MI, the F-waves were recorded (post).

We included 10 healthy volunteers (8 males; 2 females; mean age, 25.35.0years). All participants gave their written informed consent prior to the study's commencement. This study was approved by the Research Ethics Committee at Graduate School of Kansai University of Health

The environment and conditions of the F-wave recording are the same as those for previous work. The protocol of this study is as follows. For the resting trial (rest), the F-waves were recorded while the muscle was relaxed. For the MI trial, participants first learned how to perform isometric thenar muscle activity under 50% MVC as a motor task for 1min. They were then instructed to imagine the isometric thenar muscle activity under 50% MVC by holding the sensor between the thumb and index finger for 5min. The F-waves were recorded at 1, 3, and 5 min after the onset of motor imagery (1min MI, 3min MI, and 5min MI, respectively). Imme-

For statistical analysis, first, the normality of F-wave data was confirmed using the Shapiro-Wilk tests. Persistence, F/M amplitude ratio, and latency among five trials (rest, 1min MI, 3min

Sciences. The experiment was conducted in accordance with the Declaration of Helsinki.

Our previous work suggested that MI can increase spinal motor neuron excitability, and differences in the imagined muscle contraction strengths are not involved in changes of spinal motor neuron excitability. Therefore, the previous results implied that MI of isometric thenar muscle activity under slight MVC (i.e., 10% MVC) can substantially facilitate spinal motor neuron excitability. Described in the introduction, one of our final goals is to find the way that MI obtained the most beneficial effect. Hale et al. [24] suggested that spinal motor neuron excitability was gradually increased with the number of MI trials. Gentili et al. [31] proposed that a number of MI trials are necessary to improve motor performance. To obtain a more beneficial effect of MI, the number of MI practices is considered to be important. On the other hand, in the optimal duration of MI that can facilitate motor performance, the most is unclear. Previous research used various durations of MI session, which ranged from a few seconds to approximately 200min (for review, see Driskell et al. [32]). A meta-analysis by Driskell et al. [32] suggested that a longer MI session does not always provide a beneficial effect on sports performance. Furthermore, they recommended approximately 20min to achieve a more beneficial effect. Hinshaw [33] also suggested that MI for 10–15min was considered to elicit the largest effect on performance, and Twining [34] indicated that 5min is the temporal limitation when we can concentrate and perform MI. Alternatively, the influence of duration of MI on the changes of spinal motor neuron excitability is not apparent. In our previous work [10, 13, 14, 19], participants were asked to perform MI for 1min. Thus, this research aimed to investigate the influence

3.1. Purpose

42 Neurological Physical Therapy

3.2. Materials

3.3. Methods

3.4. Statistical analysis

Persistence at 1 and 5min MI was significantly greater than that at rest (Scheffe's test, \*\*p<0.01; Figure 16). Also, persistence at 3min MI was significantly greater than that at rest (Scheffe's test, \*p<0.05; Figure 16). Additionally, persistence at 1, 3, and 5min MI had similar results (Figure 16).

The F/M amplitude ratios at 1 and 3min MI were significantly greater than those at rest, at 1 min MI (Scheffe's test, \*\*p<0.01), and at 3min MI (Scheffe's test, \*p<0.05; Figure 16). However, the F/M amplitude ratio at 5min MI was similar compared with that at rest (Figure 16). Additionally, the F/M amplitude ratio at 5min MI was significantly smaller than that at 1 and 3min MI (Scheffe's test, \*p<0.05; Figure 16).

Immediately after MI, persistence and the F/M amplitude ratio recovered to the rest level (Figure 16).

Figure 16. Changes of the F-waves during MI for 5min.

There were no significant differences in latency among all five trials (Figure 16).

#### 3.6. Discussion

In our previous study, it is plausibly possible that participants did MI for 5min because the persistence and F/M amplitude ratio were increased compared with those at rest. Specifically, persistence during MI for 5min was kept significantly higher compared with that at rest. The F/M amplitude ratios at 1 and 3min MI were significantly higher compared with those at rest. However, the F/M amplitude ratio at 5min MI was significantly smaller compared with that at 1 and 3min MI. Therefore, the facilitation effect of spinal motor neuron excitability by MI may be decreased between 3 and 5min after the initial MI.

In regard to the F/M amplitude ratio at 5min MI being significantly decreased compared to that at 1 and 3min MI, there are several considerable factors. The first possible factor is the habituation of MI. MI is closely related to attentional processing [35]. Brain activation was decreased by habituation after the cognitive motor task required sustained attention (e.g., continuous performance test: CPT) for 10min. Furthermore, corticospinal excitability was diminished by habituation [36]. Also, at the spinal level, T-reflex amplitude was significantly decreased by habituation after sustained mental work load (e.g., a paced two-choice serial reaction task) for 20min [37]. Hence, it is considered that the further activation of the central nervous system and spinal level during MI might not be required by habituation.

The second possible factor is mental fatigue. Mental fatigue alters motor performance. Specifically, high-load mental cognitive tasks (e.g., incongruent Stroop task) for about 20min altered maximal force production of elbow flexor [38], and task-induced mental fatigue altered the speed accuracy of actual performance and MI [39]. Furthermore, repetitive MI led to participants having difficulties in maintaining focused attention on imagined movement. Repetitive MI of pointing tasks did significantly extend the duration of actual performance [40]. Also, in regard to influence of repetitive MI on the central nervous system excitability, repetitive MI of handgrip movements significantly decreased the MEPs amplitude compared with that at rest [41]. Considering the previous results, it is possible that mental fatigue evoked by sustained mental exertion induced significant reduction in the F/M amplitude ratio to the rest level.

In our previous study, despite reduction of the facilitation effect of the F/M amplitude ratio 5 min after MI, persistence during MI for 5min was kept at a higher level compared with that at rest. In previous research using electromyography (EMG), muscle fatigue reduced the maximal force production and mean power frequency, and it conversely increased the EMG amplitude [42]. Previous researchers interpreted these phenomena to additional recruitment of motor units, an increased firing rate, and synchronization of motor units' recruitment [43]. Furthermore, Levenez et al. [44] demonstrated that sustained dorsiflexion under 50% MVC induced decline of soleus H-reflex amplitude. Rossi et al. [45] demonstrated that sustained MVC of abductor digiti minimi induced decline of the F-wave amplitude, although the F-wave persistence was unchanged. Therefore, depression of the facilitation effect of the F/M amplitude after 5min from the onset of MI implicated decline of the individual anterior cell excitability. Further, regarding the result that persistence was kept at a higher level during MI for 5 min compared with that at rest, it is considered that there was additional recruitment and/or increasing firing rate of the anterior horn cells to compensate for the decrease of individual anterior horn cell excitability evoked by mental fatigue.

Finally, we considered the practice time and vividness of MI as a possible factor. Using MI in physical practice for learning motor skills, Twining [34] indicated that 5min is the temporal limitation when we can concentrate and perform MI. In mental chronometry, the time required for actual performance and executing it mentally was similar [46]. In other words, it was difficult for participants to perform MI accurately for more than 1min. In the present research, participants practiced isometric thenar muscle activity under 50% MVC as a motor task for only 1min. Hence, practice time for 1min might be insufficient to learn entirely the thenar muscle activity under 50% MVC. Indeed, introspective comments recorded from subjects after MI for 5min indicated that they felt difficulty in performing MI vividly with time. From the viewpoint that the time required to execute and imagine the movement is similar [46], it may be necessary to match the time of task practice and MI. However, we did not study the timedependent change of the vividness of MI precisely in the present research, and further research will be required.

#### 3.7. Conclusion

There were no significant differences in latency among all five trials (Figure 16).

be decreased between 3 and 5min after the initial MI.

In our previous study, it is plausibly possible that participants did MI for 5min because the persistence and F/M amplitude ratio were increased compared with those at rest. Specifically, persistence during MI for 5min was kept significantly higher compared with that at rest. The F/M amplitude ratios at 1 and 3min MI were significantly higher compared with those at rest. However, the F/M amplitude ratio at 5min MI was significantly smaller compared with that at 1 and 3min MI. Therefore, the facilitation effect of spinal motor neuron excitability by MI may

In regard to the F/M amplitude ratio at 5min MI being significantly decreased compared to that at 1 and 3min MI, there are several considerable factors. The first possible factor is the habituation of MI. MI is closely related to attentional processing [35]. Brain activation was decreased by habituation after the cognitive motor task required sustained attention (e.g., continuous performance test: CPT) for 10min. Furthermore, corticospinal excitability was diminished by habituation [36]. Also, at the spinal level, T-reflex amplitude was significantly decreased by habituation after sustained mental work load (e.g., a paced two-choice serial reaction task) for 20min [37]. Hence, it is considered that the further activation of the central

The second possible factor is mental fatigue. Mental fatigue alters motor performance. Specifically, high-load mental cognitive tasks (e.g., incongruent Stroop task) for about 20min altered maximal force production of elbow flexor [38], and task-induced mental fatigue altered the speed accuracy of actual performance and MI [39]. Furthermore, repetitive MI led to participants having difficulties in maintaining focused attention on imagined movement. Repetitive MI of pointing tasks did significantly extend the duration of actual performance [40]. Also, in regard to influence of repetitive MI on the central nervous system excitability, repetitive MI of handgrip movements significantly decreased the MEPs amplitude compared with that at rest [41]. Considering the previous results, it is possible that mental fatigue evoked by sustained mental exertion induced significant reduction in the F/M amplitude ratio to the rest level.

In our previous study, despite reduction of the facilitation effect of the F/M amplitude ratio 5 min after MI, persistence during MI for 5min was kept at a higher level compared with that at rest. In previous research using electromyography (EMG), muscle fatigue reduced the maximal force production and mean power frequency, and it conversely increased the EMG amplitude [42]. Previous researchers interpreted these phenomena to additional recruitment of motor units, an increased firing rate, and synchronization of motor units' recruitment [43]. Furthermore, Levenez et al. [44] demonstrated that sustained dorsiflexion under 50% MVC induced decline of soleus H-reflex amplitude. Rossi et al. [45] demonstrated that sustained MVC of abductor digiti minimi induced decline of the F-wave amplitude, although the F-wave persistence was unchanged. Therefore, depression of the facilitation effect of the F/M amplitude after 5min from the onset of MI implicated decline of the individual anterior cell excitability. Further, regarding the result that persistence was kept at a higher level during MI for 5 min compared with that at rest, it is considered that there was additional recruitment and/or

nervous system and spinal level during MI might not be required by habituation.

3.6. Discussion

44 Neurological Physical Therapy

We investigated the change of spinal motor neuron excitability during MI for 5min. Persistence was significantly increased during MI for 5min. However, the F/M amplitude ratio at 5min returned to the rest level. As a result, MI for 5min may affect spinal motor neuron excitability. Thus, the duration of MI needs to be considered.

## 4. The use of MI in clinical settings

From the results of our previous work [13, 14, 19], MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC can facilitate spinal motor neuron excitability. Furthermore, the imagined muscle contraction strength is not involved in changes of spinal motor neuron excitability. In other words, MI under slight MVC (10% MVC) can sufficiently increase spinal motor neuron excitability. In the study about duration of MI, the F/M amplitude ratio returned to rest level between 3 and 5min after initial MI. It is considered that the adequate duration of MI might be 1 or 3min.

Finally, we discuss the application of MI to patients in clinical settings. Functional reorganization of the central nervous system may be elicited after brain and spinal cord injury. After brain and spinal cord injury, motor cortex excitability decreased due to various factors, including the damage of neural substrates, loss of sensory inputs, and disuse of the affected limb [47]. The corticospinal excitability would be decreased following the significant decrease of both size and number of the corticospinal neurons [48]. Therefore, we considered that facilitating the excitability of the central and spinal neural level could be necessary for improvement of motor function. MI can increase the MEPs amplitude in patients with post-stroke [49] and spinal cord injury [50], and the F-waves post-stroke [51]. From these previous results, we believe that MI is the effective method for improvement of motor function after damage to the central nervous system.

## Author details

Yoshibumi Bunno<sup>1</sup> \*, Yuki Fukumoto<sup>1</sup> , Todo Marina2 and Chieko Onigata<sup>2</sup>

\*Address all correspondence to<EMAIL_ADDRESS>
1 Graduate School of Health Sciences, Graduate School of Kansai University of Health Sciences and Clinical Physical Therapy Laboratory, Faculty of Health Sciences, Kansai University of Health Sciences, Wakaba, Kumatori, Sennan, Osaka, Japan

2 Clinical Physical Therapy Laboratory, Faculty of Health Sciences, Kansai University of Health Sciences, Osaka, Japan

## References

[11] Taniguchi S, Kimura J, Yamada T, et al. Effect of motion imagery to counter rest-induced suppression of F-wave as a measure of anterior horn cell excitability. Clin Neurophysiol. 2008;119:1346–1352.

Author details

46 Neurological Physical Therapy

Yoshibumi Bunno<sup>1</sup>

Health Sciences, Osaka, Japan

Neurosci. 2012;6:247.

J Sports Sci. 2010;28:291–298.

2013;33:171–176.

References

\*, Yuki Fukumoto<sup>1</sup>

\*Address all correspondence to<EMAIL_ADDRESS>
, Todo Marina2 and Chieko Onigata<sup>2</sup>