astasia is a clinical postural disorder characterized by the inability to stand without 
 external support despite having sufficient muscle strength .
this symptom can be observed in 
 post - stroke patients who have experienced thalamic hemorrhage or ischemia1,2,3 , and it is frequently accompanied by falling 
 toward the contralesional side without exhibiting pushing behavior , which is a tendency to 
 actively push away from the ipsilesional side4 .
it has been reported that symptoms of astasia tend to spontaneously 
 disappear several days after stroke onset1,2,3 . 

it is thought that vertical perception has a pivotal role in maintaining upright posture in 
 humans .
one of the important vertical perceptions is subjective postural vertical ( spv ) , 
 defined as bodily vertical perception mainly derived from somatosensory information5 .
the authors of previous studies have 
 suggested that the functionality of spv influences the chance of postural disorders in 
 post - stroke patients6 .
indeed , in 
 post - stroke patients , the correlation between the degree of spv bias and that of falling 
 toward the contralesional side is very strong6 . based on these lines of evidence , it was hypothesized that abnormal 
 spv can be one of the functional mechanisms underlying postural disorders in astasia 
 patients . in the present study
, this hypothesis was tested in a single case study of a 
 post - stroke patient with prolonged astasia .
the patient was a 72-year - old man diagnosed with a right thalamic hemorrhage and 
 post - stroke astasia .
the patient s spv and ability to stand were assessed and confirmed an 
 abnormality , especially in spv .
then , to further elucidate the causal relationship between 
 the abnormal spv and the postural disorder , a 1 week program of standing training aimed at 
 regulating spv was applied and its effect on vertical perception and standing ability was 
 evaluated . during this training ,
the patient was asked to maintain his body orientation 
 vertical in reference to complementary somatosensory inputs arising from the ipsilesional 
 upper limb .
several previous studies demonstrated that somatosensory inputs arising from a 
 hand or finger , by lightly touching it to a stable object , reduce postural sway during 
 standing in healthy subjects7 , as well as 
 in post - stroke patients8 .
these findings 
 seem to imply that somatosensory input from the upper limb can be used as supporting 
 information conveying body orientation7 , 9 , 10 , 
 which may contribute to regulating somatosensory - dependent vertical perception ( i.e. , spv ) . 
 therefore , it was expected that this standing training could help the astasia patient 
 regulate abnormal spv , and thereby lead to an improvement in his postural disorder .
a 72-year - old right - handed man diagnosed with right thalamic hemorrhage including the 
 posterolateral nucleus participated in the study .
the patient started receiving standard physical therapy such as sitting , sit - to - stand , and 
 gait training on the stroke care unit 2 days after stroke onset for about an hour per day . 

sixteen days after onset , the patient was transferred to the recovery rehabilitation unit 
 and continued the physical rehabilitation and standard physical therapy for about 3 hours 
 per day .
fifty days after onset , he still had mild hemiplegia and severe somatosensory 
 dysfunction of the upper and lower limbs on the contralesional side ( table 1table 1.the patient s physical and cognitive function at each phasebefore the baselineafter the baselineafter the intervention sias - motor ( hip / knee / ankle)4/4/44/4/44/4/4knee extension force ( left / right / sum total ) ( nm / kg ) 0.26/0.38/0.64 not assessed0.28/0.36/0.65sias - sensory ( upper / lower)0/00/01/0mas ( upper / lower)1/11/11/1sara ( left / right)nose - finger test0/00/00/0heel - shin slide test1/01/01/0mmse20not assessed20scp ( standing ) ( section a / b / c)1/0/01/0/00.25/0/0fim motor total464648bed transfer445toilet transfer445sias : stroke impairment assessment scale ; mas : modified ashworth scale ; sara : scale 
 for assessment and rating of ataxia ; mmse : mini mental state examination ; scp : scale 
 of contraversive pushing ) .
in addition , he was not able to stand and gait was not possible without 
 assistance because of a tendency to fall toward the contralesional side despite not having 
 any pusher behavior ( his total score on the scale of contraversive pushing was less than the 
 cut off point11 ) .
it was thought that 
 this was not due to muscle weakness on the contralesional side , because the sum of knee 
 extension force of both sides ( 0.64 nm / kg ) was higher than the cut - off point for 
 sit - to - stand independence ( 0.40 nm / kg)12 . 

it was also assumed that the patient s postural disorders were not directly caused by severe 
 somatosensory dysfunction since it has been shown that humans can stand alone with complete 
 somatosensory loss13 . accordingly , the 
 patient was diagnosed with post - stroke astasia .
sias : stroke impairment assessment scale ; mas : modified ashworth scale ; sara : scale 
 for assessment and rating of ataxia ; mmse : mini mental state examination ; scp : scale 
 of contraversive pushing for measuring spv , the patient was seated on a tilt table ( ua - a501 , og giken , japan ) with 
 his eyes closed .
a physical 
 therapist supported the patient s body with his body from behind , acting like the backrest 
 of a chair without touching the patient with his hands .
another therapist carefully checked 
 the patient s posture from his front in order to keep his torso and head in a straight line . 

for the assessment , the tilt table was passively tilted either from the right ( ipsilesional ) 
 toward the left or from the left ( contralesional ) toward the right with a constant velocity 
 ( 2.5 degrees / s ) in the roll plane .
the initial tilting angle was set as either 5 degrees 
 toward the right ( 5 degree ) or left ( 5 degree ) with respect to the earth vertical .
while 
 the table was tilting , the patient was required to verbally indicate the time when he felt 
 his body was vertical . the table s tilting angle ( i.e. , the angle from the horizontal line ) 
 at this time was recorded as the index for spv . because of the tendency to feel that the 
 body is vertical when the body was still leaning to the side of the initial tilt5 , 14 , 15 , ipsilesional ( spv - i ) and contralesional 
 tilt conditions ( spv - c ) were separately assessed . spv - i corresponded to the condition in 
 which the table started tilting from the right ( ipsilesional ) to the left , whereas spv - c 
 corresponded to the one from the left ( contralesional ) to the right .
both spv - i and spv - c 
 were evaluated five times in a randomized order .
the patient was instructed to keep his eyes 
 closed throughout the measurement in order not to receive visual feedback about his 
 position .
since this assessment used different devices from those used in previous 
 studies6 , 14 , the intra - rater reliability of this assessment was determined by 
 evaluating intra - class correlation coefficients ( iccs ) with eight right - handed healthy 
 subjects ( age , 25.5  2.9 , mean  sd ) .
spv was measured five times per subject and the icc 
 was calculated using spss ( version 22 , ibm ) .
the icc value was 0.95 for the condition from 
 the right and 0.85 for the condition from the left , indicating the high reliability of this 
 method of measurement .
the measurement was performed under four different conditions : eyes open or closed with or 
 without holding a side cane . for the measurement with
eyes opened , specific visual reference 
 ( e.g. a vertical bar ) was not presented .
each condition was measured three times and the 
 longest duration was selected for each condition .
first , the 1 week baseline period occurred . in this week , standard physical therapy 
 including sit - stand , standing , transfer , and gait training was provided . during gait 
 training ,
the patient wore a knee - ankle - foot orthosis ( kafo ) while holding a cane or 
 parallel bars .
occupational therapy , mainly focusing on daily activities such as toilet and 
 dressing training , was also performed each day .
the total rehabilitation time was 3 hours 
 per day , 7 days per week .
spv , standing duration , and physical and cognitive function were 
 assessed before the therapy on the first day and after the therapy on the last day . in the second week
( intervention period ) , standing training ( body - tilting training ) was 
 added ( fig .
the patient was randomly tilted toward either ipsilesional 
 ( right ) or contralesional ( left ) side , then the tilt table tilted toward opposite 
 direction until he verbally indicated that his body orientation reached upright .
the subject aligned his body 
 orientation in reference to magnitude of somatosensory inputs from his ipsilesional 
 upper limb .
left : when his body orientation was upright , the magnitude of 
 somatosensory inputs was large , right ; when his body orientation was tilted , the 
 magnitude of those was small . ) .
the patient stood upright with a kafo on the contralesional leg beside the wall on 
 his non - paretic ipsilesional side .
the patient kept the ipsilesional arm close to his body 
 while extending the elbow .
then , the patient was instructed to keep the forearm , upper - arm , 
 and fingers touching the wall , in order for him to recognize the relationship between the 
 actual vertical in standing with the magnitude of somatosensory inputs from the upper limb . 

next , the patient actively tilted his body away from the wall . at this time , he was 
 instructed to keep at least his fingers touching the wall to recognize the relationship 
 between torso listing and reduced haptic inputs from the non - paretic ipsilesional upper 
 limb .
it was expected that , through 
 this training , the patient could recognize his body orientation in reference to the 
 magnitude of somatosensory inputs from the non - paretic ipsilesional upper limb . in the 
 middle of the week ,
the training setting was changed to reduce the contribution of visual 
 information . during the first 3 days , the patient performed this training about 2 meters 
 ahead of a vertical bar , which could provide the patient with a salient visual vertical 
 reference . over the next 4 days
, the patient was asked to perform the training with his eyes 
 closed and he was given verbal feedback about his body orientation for every trial . during 
 the intervention period , sit - to - stand and standing training were replaced with body - tilt 
 training , but gait training was continued .
thus , total rehabilitation time in this week was 
 comparable to that in the baseline period .
spv , standing duration , physical function , and 
 disability were assessed after the therapy on the last day of the week .
the patient was randomly tilted toward either ipsilesional 
 ( right ) or contralesional ( left ) side , then the tilt table tilted toward opposite 
 direction until he verbally indicated that his body orientation reached upright .
the subject aligned his body 
 orientation in reference to magnitude of somatosensory inputs from his ipsilesional 
 upper limb . left : when his body orientation was upright , the magnitude of 
 somatosensory inputs was large , right ; when his body orientation was tilted , the 
 magnitude of those was small .
before the baseline period , both spv - i and spv - c were biased toward the ipsilesional and 
 the contralesional side , respectively ( table 
 2table 2.the patient s spv and standing duration at each phasebefore the baselineafter the baselineafter the intervention spv - i ( degree)2.7  0.30.3  0.30.4  0.8spv - c ( degree)3.0  0.42.7  0.30.8  0.4standing duration ( sec)eyes open ( with / without cane)5/020/037/34eyes closed ( with / without cane)0/05/035/5data are presented in the form meanstandard error . for spv - i and spv - c , positive 
 value correspond to ipsilesional ( right ) tilt relative to vertical , and negative value 
 correspond to contralesional ( left ) tilt relative to vertical . ) .
the absolute value of both spv conditions was greater than that in the 
 younger healthy subjects measured for the icc ( 0.2  0.9 and 0.3  0.9 degrees under the 
 conditions where the table started tilting from the right and left , respectively ) . at the 
 end of the baseline period ,
spv - i showed greater improvement , namely getting closer to zero , 
 and remained close to zero until the end of the intervention period .
in contrast , spv - c was 
 still biased at the end of the baseline period , but finally showed improvement after the 
 intervention period .
data are presented in the form meanstandard error . for spv - i and spv - c , positive 
 value correspond to ipsilesional ( right ) tilt relative to vertical , and negative value 

the subject was able to keep standing for less than 5  s with his eyes open before the 
 baseline period .
after the baseline period , standing duration was slightly increased , 
 especially under conditions with the eyes open . standing duration under
for the assessment of physical 
 functions , functional independence measure ( fim ) scores for bed and toilet transfer were 
 improved after the intervention period ( from 4 to 5 , table 1 ) .
the present study investigated whether postural disorders observed in a post - stroke astasia 
 patient were attributed to abnormal spv .
this abnormality improved through a 1-week period 
 of body - tilting training utilizing complementary somatosensory inputs from the upper limb
. 
 in line with this improved spv , standing duration and activities of daily living ( i.e. , 
 transferring ) showed greater improvement after the 1 week intervention period .
these 
 findings suggest that abnormal spv can be one of the functional mechanisms underlying 
 postural disorders in post - stroke astasia patients , and support the effectiveness of the 
 intervention . before the baseline period
, both spv - i and spv - c were biased more greatly than that of 
 younger healthy subjects .
these results support the hypothesis that astasia observed in 
 post - stroke patients is accompanied by abnormal vertical perception , mainly in spv . in the 
 present study , the body - tilting training was applied to regulate abnormal spv and 
 investigated its effectiveness for postural disorders , in order to further investigate the 
 causal relationship between them .
interestingly , abnormal spv - i improved during the week of 
 the baseline period when standard physical treatments were applied , whereas spv - c remained 
 biased after the baseline period but improved after the week of the intervention period when 
 the body - tilting training was applied . in concordance with the improved spv - c ,
a previous study indicated that post - stroke patients show abnormal vertical perception , 
 especially when their body orientation is tilted toward the contralesional side compared to 
 when it is tilted toward the ipsilesional side16 , 
 17 .
this suggests that the abnormality 
 is more robust in spv - c than in spv - i , corresponding to the present results that spv - c 
 remained biased after application of standard physical therapy .
however , biased spv - c and postural disorders seem to be effectively improved through 
 body - tilting training with complementary somatosensory inputs from the upper limb . 

somesthetic ( somatosensory ) graviceptive inputs play a crucial role in the perception of 
 body orientation in external space6 , 18 , 19 .
light sensory inputs from touching a static object with the upper 
 limb seemed to provide enough additional useful information about body orientation to reduce 
 postural sway during standing7 , 8 . considering the present post - stroke astasia patient ,
we 
 speculate that complementary somatosensory inputs from the upper limb could be used as a 
 reference for regulating abnormal perception of body orientation ( i.e. , abnormal spv ) , which 
 resulted in improvements in standing balance , prolonging standing duration and improving 
 transferring ability in daily living .
one may claim that vestibular inputs would also change 
 by the training , which might somehow affect spv and postural control .
however , it has been 
 suggested that spv was mainly derived from bodily somatosensory information , but not 
 vestibular graviceptive information5 , 6 .
thus , we assume that possible changes of 
 vestibular inputs during the training would less effective on improvements of abnormal spv 
 bias and postural disorder .
moreover , it is possible that improvements in vertical 
 perception and postural disorders are due to spontaneous recovery rather than the effect of 
 body - tilting training .
however , we consider that the possibility of spontaneous recovery is 
 less plausible , given the fact that astasia symptoms in the present case had persisted well 
 beyond several days after stroke onset , when most patients show spontaneous recovery from 
 this symptom1,2,3 , and that his vertical 
 perception and postural disorders were greatly improved after the 1 week intervention period 
 as compared to those after the 1 week baseline period .
the present patient had a lesion in the right thalamus , including the posterolateral 
 nucleus as seen in other post - stroke astasia patients in previous studies1 , 2 . 
 the posterolateral thalamus functions to process both vestibular graviceptive20 and somesthetic graviceptive 
 information6 .
thus , the posterolateral 
 thalamus is thought to be a part of a  second graviceptive system ,  which contributes to 
 controlling body orientation21 . 

therefore , it is highly plausible that post - stroke patients who have posterolateral thalamus 
 lesions frequently present with postural disorders . while it has been reported that symptoms 
 of astasia tend to spontaneously disappear several days after stroke onset1,2,3 , the present case had symptoms more than 50 
 days after the stroke .
it might be that the present case had severe somatosensory 
 dysfunction in the contralesional side compared with the previous astasia cases , in which 
 somatosensory dysfunction in the contralesional side was absent or mild . as mentioned above , 

therefore , 
 it seems that severe somatosensory dysfunction on one side of the body might delay the 
 improvement of abnormal vertical perception , which might result in prolonged postural 
 disorders , as in the present case .
our study demonstrated the functional relationship between abnormal spv and postural 
 disorders in a post - stroke astasia patient .
however , it should be noted that the present 
 astasia patient might be a unique case , because symptoms of astasia spontaneously tend to 
 disappear several days after stroke onset1,2,3 , 
 while the present case had prolonged astasia symptoms more than 50 days after stroke .
thus , 
 it remains unclear whether the abnormal vertical perception found in the present case is a 
 common dysfunction observable in other astasia patients as well .
to systematically 
 investigate this relationship and the effectiveness of our standing training , further 
 investigation with a large number of patients is required . despite this , we believe that the 
 present case report provides useful insights into the clinical condition of post - stroke 
 astasia patients and suggests a possible option to help treat these patients .
 [ purpose ] post - stroke astasia is an inability to stand without external support despite 
 having sufficient muscle strength . 
 however , the dysfunction underlying astasia is unclear . 
 
 we tested the hypothesis that astasia is the result of an abnormal bias in vertical 
 perception , especially subjective postural vertical ( spv ) , mediated by somatosensory 
 inputs . 
 [ subjects and methods ] a patient with a right posterolateral thalamus hemorrhage 
 had a tendency to fall toward the contralesional side during standing after 8 weeks of 
 treatment . 
 spv , standing duration , and physical function were evaluated before and after a 
 1 week standard rehabilitation baseline period , and after a 1 week intervention period , 
 where standing training requiring the patient to control his body orientation in reference 
 to somatosensory inputs from his ipsilateral upper limb was added . 
 [ results ] spv was 
 biased toward the contralesional side before and after the 1 week baseline period . 
 however , spv improved into the normal range and he could stand for a longer duration after 
 the intervention period . 
 [ conclusion ] this case suggests that abnormal spv is one of the 
 functional mechanisms underlying astasia , and it indicates the effectiveness of standing 
 training with somatosensory information to improve abnormal spv and postural 
 disorders . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION