the sensory strategy for postural control involves the visual , vestibular , and 
 somatosensory systems . in particular ,
the vestibular system provides information regarding 
 head position and movement with respect to gravity and inertial forces1 .
more specifically , the vestibulo - ocular and vestibulospinal 
 reflexes are significantly associated with postural control , eye movement , and neck and 
 trunk rotation2 .
a previous study reported 
 that stroke patients and healthy elderly adults exhibit increased postural instability 
 during head rotations in the standing position compared to that during static standing3 .
with regard to vestibular information 
 related to cortical activation , areas of the superior temporal gyrus related to postural 
 control are activated in subjects who primarily receive vestibular sensory input in the 
 standing position4 . increased brain 
 activity has also been observed in the supplementary motor area during adjustment for 
 postural perturbation5 .
however , it is 
 unknown whether neck and trunk rotation speeds influence postural perturbation and cortical 
 activation . thus , measuring changes in cortical activation and postural stability 
 simultaneously would provide valuable information regarding vestibular function in 
 activities of daily living .
the purpose of this study was to determine if different neck and trunk rotation speeds 
 influence standing postural stability or frontal and temporal cortical activity during 
 rotation in healthy young adults .
twelve healthy volunteers ( mean age , 25.8  2.1  years ) participated in this study . 

self - reported history of vestibular , balance , and mobility impairment was obtained from all 
 subjects .
written informed consent was taken from all volunteers prior to study 
 participation , and the study protocol was approved by the ethics committee of university of 
 saga , japan .
the following three parameters were measured simultaneously for each subject : brain 
 activity , center of pressure ( cop ) , and head perturbation .
evaluations were performed with a 
 block design comprising an initial resting during standing condition ( 15 seconds ) , a task 
 condition ( 30 seconds ) , and a second resting during standing condition ( 15 seconds ) .
evaluation of cortical activity during postural stability requires an accurate definition 
 of rotation stimulation .
postural stability was evaluated using a force platform ( gs-31 ; 
 anima , inc . ,
tokyo , japan ) and head sensor ( tsnd121 ; atr - promotions , kyoto , japan ) .
a custom 
 turn - table operated by one of the experimenters was placed on the platform to assess 
 postural perturbation .
subjects were asked to stand barefoot on the turn - table with their 
 feet together ; the platform rotated at an angle of up to 180. subjects were randomly 
 assigned to either the high- or low - rotation speed condition ( 180/s or 90/s peak angular 
 velocity , respectively ) . to avoid excessive eye movement during testing
, subjects were asked 
 to keep their head as still as possible while focusing on a target placed at a distance of 
 5  m in front of them .
subjects were permitted to familiarize themselves with the platform s 
 movement prior to the measurement . to evaluate postural stability , we measured cop for both , 
 area of body sway and total body length .
a sensor was placed on the top of each subject s 
 head to detect perturbations .
the following two head movements were evaluated : head velocity 
 was measured in the anterior 
posterior , left - right , and up - down directions , and angular 
 velocity was measured in the roll , pitch , and yaw planes . cop positions and head 
 perturbations
cerebral cortex activity was evaluated using a functional near - infrared spectroscopy 
 ( fnirs ) system ( omm-3000 ; shimadzu corp . , kyoto , japan ) equipped with 16 light sources and 
 16 detectors .
this system captured changes in oxygenated hemoglobin ( oxyhb ) level through 51 
 channels .
we adopted an interoptode distance of 3.0  cm from the near - infrared light source 
 to ensure propagation to the gray matter underlying the optodes .
the light source at the 
 center of the third row was set in a position that corresponded to cz , t3 , t4 , f3 , and f4 of 
 the 1020 international system .
we defined each fnirs channel by the midpoint of the 
 corresponding light source - detector pair .
regarding anatomical information , the location of 
 each optode on the plastic cap was marked using a 3d digitizer ( fastrak ; polhemus , inc .
the estimated locations of the fnirs channels on the cortex were 
 transformed using the affine transformation matrix in the fusion software program ( shimadzu 
 corp ) .
data were analyzed with nirs - spm using matlab 2014a software ( the mathworks , inc . , 

all statistical analyses were performed using spss version 21 software ( ibm corp . , armonk , 
 ny , usa ) , with the significance level set at p < 0.05 .
data collected by the head sensor 
 were used to calculate the absolute value at each plane during platform rotation . each 
 subject s cop and head movement
the wilcoxon signed - rank test was used to assess differences in postural stability 
 between high and low rotation speeds . using the data obtained from fnirs , task - related 
 cortical activity during each condition
significant differences were found between the high- and low - speed rotations with regard to 
 head perturbation in the roll , pitch , and yaw planes ; cop of the ellipse area ; and 
 displacement ( all p < 0.01 ) ( table 
 1table 1.comparison of head sensor and center of pressure ( cop ) measurements between 
 different neck and trunk turning speedslow turning speedhigh turning speedhead sensorvelocityanterior  posterior , m / s16.43 ( 10.98)21.02 ( 13.88)left  right , m / s5.99 ( 4.21)5.97 ( 4.24)up  down , m / s87.04 ( 3.75)86.63 ( 3.95)angular velocityroll plane , deg / sec2.16 ( 0.94)5.03 ( 1.41)*pitch plane , deg / sec1.61 ( 0.19)2.86 ( 0.88)*yaw plane , deg / sec4.21 ( 1.69)10.39 ( 6.47)*coparea of body sway , cm13.8 ( 4.9)36.2 ( 18.6)*total body length , cm105.9 ( 21.6)303.5 ( 113.9)*all values are presented as median ( interquartile range ) . *
p < 0.01 ) . in both , high- and low - speed rotation conditions ,
oxyhb levels were not 
 significantly different between the resting and task conditions ( all p > 0.05 ) .
the aim of the present study was to determine whether different neck and trunk rotation 
 speeds influence standing postural stability or frontal and temporal cortical activity 
 during rotation .
there was an increase in the subjects cop and head perturbation in the 
 roll , pitch , and yaw planes during high - speed rotation .
with regard to movement strategies , 
 ankle and hip strategies are critical for fine motor coordination and dynamic motor 
 coordination , respectively1 .
the high 
 rotation speed in this study increased body perturbation in order to control postural 
 stability ; this would affect both ankle and hip strategies .
moreover , a previous study 
 showed that the obliquus capitis inferior , rectus capitis posterior major , and splenius 
 muscle responses are affected during body rotation when the head position is fixed2 .
these muscles have a high spindle density , 
 and a high rotation speed could be one factor that allows for highly sensitive postural 
 control .
the fnirs results in this study showed that oxyhb levels did not increase significantly 
 during high- or low - speed rotation compared to those in the resting condition . regarding the 
 effect of rotation during standing
, automatic postural responses suggest that the 
 spinocerebellum and basal ganglia play complementary roles in adapting postural responses to 
 changing conditions7 .
the cerebral cortex 
 exerts more control over anticipatory postural adjustments than automatic postural 
 responses7 ; therefore , neck and trunk 
 rotation during standing may not significantly activate the cerebral cortex .
thus , 
 regardless of rotation speed , rehabilitative neck and trunk actions might be able to 
 activate automatic postural responses .
on the other hand , the vestibular system senses head 
 position during tilting and acceleration1 . 

one reason for the lack of significant differences between speed conditions could be that 
 subjects were asked to keep their head as still as possible during platform rotation .
first , although spinal reflexes are 
 associated with postural stability , they were not evaluated here .
second , in experimental conditions , the distance between 
 a subject and a visual target is usually set at 2 m , but we chose 5  m due to space 
 restrictions .
in addition , the scalp and the skull could have interfered with fnirs signal 
 measurement , and fnirs fiber movement during neck and trunk rotation could have introduced 
 an artificial noise source .
future studies should employ other neuroimaging methods to 
 clarify the neural mechanisms of postural control .
 [ purpose ] the aim of the present study was to determine whether different neck and trunk 
 rotation speeds influence standing postural stability or frontal and temporal cortical 
 activity during rotation in healthy young adults . 
 [ subjects and methods ] twelve healthy 
 volunteers participated in this study . a custom turn - table operated by one of the 
 experimenters 
 was placed on a platform to assess postural perturbation . 
 subjects were 
 asked to stand barefoot on the turn - table in an upright position with their feet together , 
 and measurements were obtained during high- and low - speed rotations . 
 postural stability 
 was tested using a force platform and a head sensor . 
 cerebral cortex activity was measured 
 using functional near - infrared spectroscopy . 
 brain activity , center of pressure , and head 
 perturbation were measured simultaneously for each subject . 
 [ results ] significant 
 differences were found in the center of pressure and the head angular velocity between 
 high- and low - speed rotations . 
 however , compared to baseline , oxygenated hemoglobin levels 
 were not significantly different during high- or low - speed rotations . 
 [ conclusion ] 
 automatic postural responses to neck and trunk rotation while standing did not 
 significantly activate the cerebral cortex . 
 therefore , the response to stimuli from the 
 feet may be controlled by the spinal reflex rather than the cerebral cortex . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION