therapeutic approaches to stroke recovery include neurodevelopmental treatment , functional 
 electric stimulation , constraint - induced therapy , and robot - assistance training1,2,3,4 . also , motor imagery and action observation are applied to the rehabilitation of stroke 
 patients in the form of cognitive intervention methods5 . motor imagery is a conscious cognitive processing of the brain that induces activation of 
 muscles related to actual motion output by imagining motions6 . during motor imagery , activation of the premotor area , 
 supplementary motor area , cingulate gyrus , parietal lobe , basal ganglia , and cerebellum is 
 known to occur in a manner similar to that during actual performance of activities7 . some studies have reported the 
 effectiveness of motor imagery not only in recovering from injuries and improving motor 
 skills in healthy individuals and athletes8 , but also in enhancing motor skills in stroke patients9 . however , the effects of motor imagery 
 differ according to the individual ability of imagery , functional level of the learner , and 
 cooperation and concentration of the learner5 . action observation , based on the same neural mechanism as motor imagery , has been suggested 
 as an alternative intervention that can complement the limitations of motor imagery 
 training10 . action observation , which 
 is based on mirror neurons that are active both when people perform an action and when they 
 watch it being performed , is a cognitive intervention technique that is applied to patients 
 with motor disorders as well as athletes and healthy people to improve and learn motor 
 skills , and it is known to be effective in enhancing functional activities in the 
 elderly11 . however , while there have been many studies that examined immediate changes in brain 
 activity caused by either action observation or motor imagery12 , studies focusing on long - term changes in brain activity taking 
 several weeks at least to be caused have been lacking . the aim of this study is to determine 
 the changes in the chronic stroke patient 's brain activity after four weeks of action 
 observation training and motor imagery training . mean  sd ; mmse - k : mini mental state examination of 59 consecutive registered stroke patients , 30 patients who fulfilled the selection 
 criteria were enrolled in this study . detailed inclusion criteria were as 
 follows : ( 1 ) having a first - time ischemic or hemorrhagic stroke , ( 2 ) over six months since 
 onset , ( 3 ) able to walk independently more than 10 m , ( 4 ) more than 24 points on the mini 
 mental state examination , and ( 5 ) fewer than 36 points on the vividness motor imagery 
 questionnaire-2 . exclusion criteria were as follows : ( 1 ) severe cognitive disabilities , such 
 as unilateral neglect , dementia , and depression , and ( 2 ) severe aphasia . after baseline 
 measurements were obtained , patients were randomly assigned to groups by selection using 
 sealed envelopes . participants in the action observation group participated in 20 sessions of 30-min 
 observation training five times per week . the training program of the action observation 
 training group consisted of viewing a task video for 20 minutes , followed by physical 
 training with a therapist for 10 minutes based on the video . the models in the of videos 
 were normal adult males and females in their 50s , which was similar to the mean age of the 
 patients , so as to raise their levels of concentration with regard to understanding the 
 motions . the training program consisted of four stages , according to the content , including 
 trunk flexion , trunk rotation , sit to stand , and crossing obstacles . participants in the motor imagery group had attended their training for 30 minutes , 5 times 
 a week for 4 weeks . motor imagery was conducted for 20 minutes according to the motor 
 imagery program played through a computer speaker , and the participants then underwent 
 physical training for 10 minutes based on the training contents . all participants in this 
 study underwent neurodevelopmental therapy for 30 minutes , twice per day , five days per week 
 for a period of four weeks , according to the schedule of the institution in which they were 
 hospitalized . the exercise program included training of the trunk for learning supine to 
 rolling movements , sit to stand , and normal gait pattern . a poly - i ( laxtha inc . , daejeon , korea ) was used to take eeg measurements . measurement of 
 eeg is likely to be influenced by internal factors , such as eye movements and blinks and 
 hiccups , and external factors , including temperature , illuminance , noise , and smell of a 
 room ; therefore , measurements were performed in a separate quiet space with a constant 
 temperature and illuminance . each eeg 
 measurement was recorded for one and a half minutes while the subjects were instructed to 
 maintain a comfortable posture with the eyes closed and refrain from speaking or moving in 
 order to minimize interference from artifacts . eeg electrodes were attached to four places on the scalp using the monopolar derivation 
 method . the four places included frontopolar 1 ( fp1 ) , frontopolar 2 ( fp2 ) , central lobe 3 
 ( c3 ) , central lobe4 ( c4 ) , occipital lobe 1 ( o1 ) , occipital lobe 2 ( o2 ) in order in 
 accordance with the international 1020 system . moreover , a reference electrode and a ground 
 reference electrode were placed behind the right earlobe and the left earlobe , respectively . the electrodes used were gold - plated disc - shaped eeg electrodes ( elefixz-401ce , nihon 
 kohden , tokyo , japan ) . for eeg data analysis , a quantitative analysis was conducted using telescan2.98 ( laxtha 
 inc . , daejeon , korea ) . among the overall eeg raw data , 70 seconds of each measurement after 
 excluding the first and last ten seconds was analyzed . raw eeg data were converted into 
 frequencies using a fast fourier transform ( fft ) . then relative alpha power ( 813/450  hz ) 
 and relative beta power ( 1320/450  hz ) were analyzed . spss statistical package version 17.0 ( spss inc . , chicago , il , usa ) was used for 
 statistical analysis.pairedt-tests were used to determinewhether the changes in relative 
 alpha power and relative betapower between before and after trainingdiffered significantly 
 within a group.one-way anova was used to determine whether values that changed between 
 before and after training differed significantly between the three groups . mean sd ; * p<0.05 ; fp1 , frontopolar 1 ; fp2 , frontopolar 2 ; c3 , central 
 lobe 3 ; c4 , central lobe 4 ; o1 , occipital lobe 3 ; o2 , occipital lobe 2 general characteristics of the subjects are shown in table 1 , and there were no significantly differences between the three groups.in 
 alpha power , asignificant decrease in fp1 , from 0.0864 before training , to 0.0546 after 
 training ( p<0.05 ) , and in fp2 , from 0.091 to 0.0592 ( p<0.05 ) , was observed in 
 theaction observation group.numerical changes were observed in other channels of action in 
 the action observation and motor imagery groups , however , no significant differences were 
 observed ( table 2).in beta power , a significant 
 decrease in fp2 , from 0.0681 before training , to 0.1096 after training ( p<0.05 ) , and in 
 c3 , from 0.1110 to 0.1512 ( p<0.05 ) , was observed in theaction observation group ( table 2 ) . through a certain period of training the brain learns to control brainwaves within a 
 certain range and remembers the results for a long period of time13 . this study aimed to identify the changes in brain 
 activity during action observation training , motor imagery training , and physical training 
 by observing changes in eeg during each type of training . eeg signals can be divided into spontaneous potentials ( sp ) and evoked potentials ( ep ) . 
 then sps can be classified into five types according to the frequency domain , among which 
 alpha power , between 813  hz , is usually detected in a comfortably conscious state when an 
 individual is relaxed , comfortable with the eyes closed , or meditating14 . alpha power increases in a relaxed state or a state of a 
 moderate level of awareness , while it decreases as the intensity of cognitive activity 
 increases15 . according to the results of this study , a lower occurrence frequency of alpha power was 
 observed inthe action observation group , compared with the motor imagery group and the 
 physical training group , and significant differences were revealed between before and after 
 training in fp1 and fp2 . this suggests that even though motor imagery induced an increase in 
 cognitive activity , action observation training led to a higher level of cognitive activity 
 than motor imagery or physical training did . in c3 and c4 , decreases in relative alpha 
 power , though not significant , were observed as in the other areas . such responses in the 
 parietal lobe indicate that brain activity occurred not in a localized area but across all 
 brain areas while information about stimuli given during observation were processed16 . action observation is known to activate 
 the cerebral cortex more effectively than motor imagery because it involves the direct 
 activity of multisensory systems and forms clear motor representations of given tasks10 . in this study , the action observation 
 group was encouraged to watch the task video , composed of several stages , intensively for a 
 certain period of time and then to understand the order of the motions and details in the 
 mind . in comparison , the motor imagery group was instructed to imagine relevant motions 
 based solely on auditory signals . therefore , subjects who had not normally experienced the 
 motions in real life presumably found it difficult to form clear representations of the 
 tasks . in addition , decreased concentration during motor imagery training may have hindered 
 learning , and this is probably why the action observation group showed a relatively lower 
 occurrence frequency of relative alpha power than the other two groups . beta power , between 
 1235  hz , is detected when an one is engaged in solving problems that require concentration 
 including when one 's cognitive effort increases with the purpose of performing difficult 
 tasks , one is thinking logically , or one 's conscious activity regarding the body rises17 . in most cases , alpha power is suppressed , 
 while beta power increases , when an individual is executing tasks that require concentration 
 rather than remaining in a stable state18.the activation of beta power is known to reflect an increase in 
 cognitive function resulting from cognitive information processing activity at an intense 
 level19 . pfurtscheller et al.16 analyzed the occurrence frequencies of 
 beta power in the sensorimotor area while subjects were imagining foot , hand , and tongue 
 movements . the results revealed that there was no significant change during the imagination 
 of tongue movements , while the occurrence frequencies of beta power significantly increased 
 during the imagination of foot or hand movements . these results suggest that the intensity 
 of cognitive activity required can vary according to the characteristics of the task . the 
 action observation training program adopted in this study was composed of task - oriented 
 training categories , such as a trunk exercise while sitting , horizontal weight shift while 
 standing , level walking , and obstacle crossing while walking . these types of training are 
 thought to have increased the subjects ' levels of cognitive activity required to understand 
 the motions . furthermore , action observation training , unlike motor imagery training , allows 
 participants to identify the differences between their internal plans and observed models 
 while observing their motions20 , and the 
 activation of such a feedback mechanism can raise the level of cognitive activity in 
 participants . the results of this study also suggested that the action observation group 
 showed higher relative beta power values than the other two groups and indicated significant 
 differences in fp2 and c3 between before and after training . in the premotor cortex , the 
 neurotransmission process occurs in real time from the cerebral cortex to relevant muscles 
 both when people perform an action and when they watch it being performed21 , and such activity of the cerebral cortex 
 seems to have enabled the action observation group to show relatively high levels of 
 relative beta power . the results revealed that action observation training induced higher levels of cognitive 
 activity than motor imagery or physical training did . nevertheless , for stroke patients and others 
 with central nervous system injuries , in particular , motor learning through action 
 observation training is expected to be more effective in terms of the provision of easier , 
 clearer representations of motions .
[ purpose ] the purpose of this study was to compare the effects of action observation 
 training and motor imagery training on recovery from chronic stroke . 
 [ subjects ] thirty 
 patients ( who were over six months post stroke ) participated in this study and were 
 randomly allocated to three groups . [ methods ] the action observation training group 
 practiced additional action observation training for five 30-minute sessions over a 
 four - week period . 
 the motor imagery training group practiced additional motor imagery 
 training for five 30-minute sessions over a four - week period . 
 electroencephalogram were 
 used to compare brain waves between the three groups . 
 [ results ] the action observation 
 group showed significant changes in relative alpha power in fp1 and fp2 and relative beta 
 power in fp2 and c3 . 
 [ conclusion ] action observation induces higher levels of cognitive 
 activities than motor imagery and physical training . action observation is expected to be 
 more effective for stroke patients .