galvanic vestibular stimulation ( gvs ) activates the afferent vestibular nerve and affects 
 the vestibular and peripheral areas of the cerebral cortex . like transcranial direct current 
 stimulation ( tdcs ) , gvs is a non - invasive electrical stimulation method that can stimulate 
 the brain safely without serious side effects1 . electrostimulation using gvs can be utilized to analyze 
 electrically induced postural balance response by applying a direct current to the mastoid 
 process behind the ear and the stimulation of the vestibular nerve2 . the bipolar gvs cathode depolarizes the stimulated region 
 for excitation , while the anode hyperpolarizes the stimulated region for suppression3 . when these stimuli deliver signals from the 
 anode and cathode to the vestibular system , the posture starts to sway towards the 
 anode4 . most studies on gvs were related 
 to balance control5 , but recent studies on 
 the effects of gvs on memory or cognitive reactions have been reported . such studies report 
 gvs has a good effect on memories related to sight6 , 
 7 . park8 report gvs has a good effect on cognition related to event - related 
 potential . furthermore , some studies report tdcs not only enhances exercise function , but 
 also positively affects cognitive reaction9 therefore , 
 how gvs enhances exercise function and the cerebral cortex in relation to exercise requires 
 further study . therefore , the present study examined the effects of gvs on movement - related 
 cortical potential ( mrcp ) . this study was approved by the research 
 ethics committee of kwangju women s university . the subjects were randomly divided into two 
 equal groups : the gvs and sham groups . the general features of the subjects are presented in 
 table 1table 1.general characteristics of the subjects ( n = 40)age ( years)height ( cm)weight ( kg)gvs ( n = 20)21.0  0.9160.8  5.053.5  5.4sham ( n = 20)21.4  1.7162.5  6.255.6  8.7 . gvs was conducted using a galvanic vestibular stimulator ( endomed 482 , 
 enraf - nonious , netherlands ) . the subjects assumed a comfortable sitting position and closed 
 their eyes . before attaching a disposable adhesive electrode ( hrtc32 , hurev , south korea ) electrodes were subsequently attached to both 
 mastoid processes ; the anode and cathode were applied to the right and left mastoid 
 processes , respectively . the pulse duration was 100  ms , and the inter - pulse duration was 
 900  ms pulse current ( triangular waveform ) . meanwhile , in the sham group ( no 
 stimulation ) , the electrodes were attached at the same locations ; the subjects group assumed 
 a comfortable sitting position and closed their eyes . mrcp was measured by electroencephalography ( eeg ) ( lxe5208 , laxtha , south korea ) and 
 electromyography ( emg ) ( mp150 , biopac , usa ) . the output signals were measured using the eeg ; 
 these were input from the mp150 via a cable and analyzed using acqknowledge version 4.0 
 ( biopac , usa ) . the subjects were instructed not to move or talk except while performing the 
 visual stimulation tasks in a comfortable sitting position . before mrcp measurement , the 
 attachment points were washed with alcohol swabs to eliminate substances , so that the skin 
 impedance would be less than under 5 k. for the eeg , an ag / agci electrode was attached to 
 the fz , c3 , cz , and c4 areas using an international 1020 system ; the ground and reference 
 electrodes were attached to the left and right mastoid processes , respectively . the 
 predetermined values for measurement were as follows : 256  hz sampling rate and 1,250 v 
 gain . an disposable adhesive electrode ( 2223h , 3 m , south korea ) was used for surface emg ; a 
 recording electrode was attached to the abductor pollicis brevis of the left hand ( i.e. , 
 non - dominant side ) , and the ground electrode was attached to the medial epicondyle . the skin 
 was washed with an alcohol swab beforehand , and the emg sampling rate was set at 1,000  hz . pictures ( i.e. , information on the exercise performance ) were projected on a monitor and 
 included three kinds of stimuli : flowers , animals , and nature ; all pictures were 400  500 
 pixels and were alternately projected 50 times using superlab version 4.5 ( cedrus , usa ) . fifty distinguishable flowers , animals , and nature pictures were shown every 5 s. the 
 subjects were instructed to abduct the thumb of their non - dominant hand every time the 
 picture was changed . analysis of the signals revealed an average of 50 signals over 4  s : 3- 
 and 1-s signals before and after the beginning of the activity , respectively , with the 
 standard being when the muscle activity started on the surface emg . the fz , c3 , cz , and c4 
 areas as well as the peak - to - peak ratio of each section of bereitschaftspotential ( bp ) , 
 negative slope ( ns ) , and motor potential ( mp ) of the mrcp were subsequently analyzed . there were no significant differences in the bp , ns , or mp in the fz or cz area ( table 2table 2.changes in mrcpareagroupbp ( mv)ns ( mv)mp ( mv)prepostprepostprepostfzgvs0.031  0.0340.023  0.0090.100  0.1190.161  0.2230.237  0.1930.27  0.186sham0.024  0.0080.019  0.0080.083  0.1310.064  0.0940.288  0.2610.206  0.187c3gvs0.023  0.010.021  0.0090.054  0.0490.062  0.0440.164  0.1430.181  0.107sham0.024  0.0090.016  0.0060.052  0.0720.04  0.050.156  0.1340.146  0.116czgvs0.022  0.0080.038  0.0760.068  0.050.062  0.0430.154  0.1130.174  0.09sham0.026  0.010.016  0.0070.055  0.0640.043  0.0450.173  0.1220.186  0.178c4gvs0.021  0.0080.038  0.0710.053  0.0550.061  0.0470.148  0.0980.165  0.092sham0.020  0.0080.015  0.0060.057  0.0650.039  0.040.173  0.1330.147 there was no significant difference in fz or cz after gvs . at the c3 area , 
 there was a significant difference in the bp with respect to time 
 ( f(1,38 ) = 6.603 , p = 0.014 ) and a significant 
 interaction effect in the ns ( f(1,38 ) = 4.709 , p = 0.036 ) ; 
 however , there was no significant difference in the mp . at the c4 area , there was a 
 significant interaction effect in the ns ( f(1,38 ) = 5.199 , 
 p = 0.028 ) and mp ( f(1,38 ) = 5.076 , p = 0.030 ) . ) . in the c3 area , the bp differed significantly with respect to time 
 ( f(1,38 ) = 6.603 , p = 0.014 ) and there was a significant 
 interaction effect in the ns ( f(1,38 ) = 4.709 , p = 0.036 ) . in 
 particular , the amplitude of the ns increased greatly in the gvs group , but there was no 
 significant change in the mp . in the c4 area , there was only a significant interaction 
 effect in the ns ( f(1,38 ) = 5.199 , p = 0.028 ) and mp 
 ( f(1,38 ) = 5.076 , p = 0.030 ) . meanwhile , the amplitudes of the 
 ns and mp decreased in the sham group but increased in the gvs group . there was no significant difference in fz or cz after gvs . at the c3 area , 
 there was a significant difference in the bp with respect to time 
 ( f(1,38 ) = 6.603 , p = 0.014 ) and a significant 
 interaction effect in the ns ( f(1,38 ) = 4.709 , p = 0.036 ) ; 
 however , there was no significant difference in the mp . at the c4 area , there was a 
 significant interaction effect in the ns ( f(1,38 ) = 5.199 , 
 p = 0.028 ) and mp ( f(1,38 ) = 5.076 , p = 0.030 ) . in the c3 and c4 areas , which are the primary motor areas , the amplitude of the ns 
 increased ; meanwhile , in the c4 area , the amplitudes of the ns and mp increased . wardman et 
 al.10 reports gvs in a standing 
 position stabilizes head movement , changing cognitive ability and proprioception . park8 investigated the effects of gvs ( 30  ms pulse 
 duration and 700  ms inter - pulse duration ) on normal cognitive reaction and found that the 
 cognitive reaction time decreased . also it was found that n100 and p300 latency decreased , 
 n100 and p300 amplitude increased . park8 
 suggested that gvs stimulates the vestibular system , interacts with the cerebral cognitive 
 area , and enhances cognitive ability . mrcp consists of negative and positive potential ; 
 negative potential is divided into the bp and ns11 . the ns appears before the movement , and the cortical activity is 
 related to the movement activity plans and practices11 . in addition , the ns ( or late bp ) in voluntary movement , and mp can 
 be used to analyze the cortical activity in accordance with the direct voluntary movement ; 
 there have been many studies about the factors affecting the cortical activity determined by 
 analyzing the amplitude and incubation period of the bp , ns , and mp , which are elements of 
 mrcp14 . on the basis of this paradigm , 
 the amplitudes of the bp , ns , and mp were analyzed after gvs in the present study . the 
 results show there was no difference in the amplitude of the bp section , which is a gradual 
 negative potential occurring 2  s before movement . on the contrary , the amplitude of the ns , 
 which is a rapid negative potential occurring 0.1  s before muscle activity after the bp in 
 the c3 and c4 areas , increased after gvs . this shows gvs has a greater effect on hand 
 movement plans and practice immediately before movement . in addition , the amplitude of the 
 mp , which is the potential occurring after movement , increased only in the c4 area after 
 gvs . vines el al.15 reported that 
 stimulating a motor region directly , or indirectly by modulating activity in the homologous 
 region on the opposite hemisphere , can affect motor skill acquisition , presumably by 
 facilitating effective synaptic connectivity . the functions of the brain are interconnected 
 via the commissural fibers of the corpus callosum in the motor cortex . galvanic vestibular 
 stimulation increases the negative slope and motor potential amplitudes of the homonymous 
 brain cortex area , which controls hand function and motion - related cortical potential , and 
 the negative slope amplitude of the opposite cortical area , thus activating the brain areas 
 for hand function .
[ purpose ] this study examined the effects of galvanic vestibular stimulation on 
 motion - related cortical potential . [ subjects and methods ] fourty healthy female adult 
 subjects each received galvanic vestibular stimulation or sham treatment . for galvanic 
 vestibular stimulation , 
 the anode and cathode were applied to the right and left mastoid 
 processes , respectively , for 10 minutes . 
 motion - related cortical potential was tested pre- 
 and post - treatment . to measure motion - related cortical potential , surface electromyography 
 signals were generated by 50 thumb abductions with electrode application on the abductor 
 pollicis brevis of the left ( i.e. , non - dominant ) hand . 
 [ results ] the negative slope 
 cortical potential on the c3 area ( i.e. , dominant hand ) and cortical negative slope and 
 motor potential on the c4 area ( i.e. , non - dominant hand ) showed significant interaction 
 effects . 
 the galvanic vestibular stimulation group showed an increased negative slope 
 amplitude in the c3 area , and increased negative slope and motor potential amplitudes in 
 the c4 area compared to the sham group . 
 [ conclusion ] galvanic vestibular stimulation 
 increases the negative slope and motor potential amplitudes of the homonymous brain cortex 
 area , which controls hand function and motion - related cortical potential , and the negative 
 slope amplitude of the opposite cortical area , thus activating the brain areas for hand 
 function .