cerebral palsy ( cp ) results from early brain injury , either pre- or perinatal , and affects 2 - 3 in 1000 children . approximately 30% of children with cp have hemiparesis , which manifests as motor impairments and weakness on one side of the body and causes substantial functional impairment in day - to - day tasks . beyond unilateral impairments , children with hemiparesis ( ch ) also have impairments in bimanual coordination . several types of intervention have shown success in improving hand function in hemiplegia , the most common of which are constraint induced movement therapy ( cimt ) , which involves unimanual training . another less studied therapy is hand - arm bimanual intensive therapy ( habit ) [ 4 , 5 ] , which involves practice of tasks requiring two hands in order to develop use of the affected hand and improve coordination . advanced mri methods , including functional magnetic resonance imaging ( fmri ) and diffusion tensor imaging ( dti ) , have been shown to provide important information in the evaluation of cp and therapy response assessment . fmri studies have shown abnormal patterns of activation with a shift towards bilateral activation in ch . reduced white matter ( wm ) integrity in corticospinal tracts in the affected hemisphere was also shown using various diffusivity indices , corresponding to severity of hand function impairment . however , little is known about changes in brain structure and function following motor interventions in ch since few studies have used serial imaging . a recent systematic review of the literature found just seven studies , all with small samples ( 310 children ) . while research into brain plasticity following rehabilitative interventions in stroke patients is more abundant [ 1113 ] , the later time of injury prevents comparison with unilateral cp , which commonly results from pre- or perinatal injury . the existing studies describing neuroplastic changes following treatment involved either virtual reality intervention   or most often unimanual interventions , such as cimt [ 10 , 15 , 16 ] . a review of the literature reported enlargement of the primary hand motor area ( m1 ) in the affected hemisphere following intervention , with no consistent effects in the less affected hemisphere . a previous study reported change in li towards unilateral pattern associated with greater improvement in motor function after cimt treatment . yet neural changes occurring after bimanual intervention have not been previously described . the current study sought to characterize brain plasticity following bimanual intervention in children with hemiparesis , via serial behavioral assessment and mr imaging , and to examine the association between brain and behavior changes . the study was approved by the institutional review board and national research ethics committee of the hospital , and fully informed consent was obtained from parents and assent from children . 12 children with hemiparesis ( 6 females , mean age 11  3.6 years ) were recruited from the pediatric neurology unit at the tel aviv sourasky medical center and associated child development centers to a magic - themed habit intervention in 2011 . the subjects in the current study are part of a larger cohort of ch . only children with longitudinal imaging additional inclusion criteria were clinical signs of spastic hemiparesis , attendance in mainstream education , and independence of mobility . exclusion criteria were any overt seizure activity , initiation of motor therapy or musculoskeletal treatment in the last 6 months , prior surgical intervention , and contraindication to mri . level of mobility and functional capacities of the children were confirmed via the gross motor function classification system ( gmfcs )   and manual ability classification system ( macs )   where higher scores represent greater restrictions to mobility and function . children were included if gmfcs  ii and macs  iii with skills ranging from more mild physical restrictions in mobility and handling of objects to considerable difficulty , thus may use mobility aids and require help to prepare and or modify activities . eight children participated in the magic habit day camp intervention ( 60 hours over 2 weeks ) and were assessed for hand motor function on 3 occasions : ( 1 ) before intervention , ( 2 ) immediately after intervention , and ( 3 ) 6 weeks following intervention . six of them underwent 3 mri scans at the same time points ( see figure 1 ) . the remaining two children ( subjects 2 and 8) underwent only two mri scans ( before and immediately following intervention ) . four children participated in an outreach home - based magic habit program ( a weekly clinical attendance with 2 hours per day of bimanual training monitored by a weekly diary ) for 6 weeks ( total of 60 hours ) and were assessed for hand motor function on 2 occasions ( before and after intervention ) . these children had only two mri scans ( before and immediately following intervention ) , except for one child ( subject 12 ) who was excluded after the first scan due to substantial head movements and inability to remain still in the scanner . to set a child friendly atmosphere and improve data quality , training in a mock scanner preceded the mri scans and during the structural series the children watched an animated movie of their choice . in addition , the child 's guardian accompanied the child in all study stages including the scans . the macs classifies ability to handle objects in important daily activities across a five - point scale ; children at level i handle most objects easily and at level v they are severely limited in their ability . hand motor function was assessed at each of the time points with 2 performance tests , assessed by trained therapists and a self - report questionnaire : the assisting hand assessment ( aha ; version 4.3 ) : a standardized test of spontaneous use and performance of a weaker / affected hand during bimanual interactions in functional / play based tasks with good reliability and validity . videos were scored by trained therapists blinded to intervention status.jebsen-taylor test of hand function ( jtthf ) : a standardized timed test measuring manual dexterity ( modified by eliminating the writing task ) with reliability and normative data reported for children . a three - minute limit was set for each task with a maximum overall score of 1080 seconds across the 6 tasks.the children 's hand experience questionnaire ( cheq ) : a 29-item questionnaire exploring independent participation and skilled use of an affected / hemiplegic hand in daily bimanual activities and reported competence and worry / confidence . the assisting hand assessment ( aha ; version 4.3 ) : a standardized test of spontaneous use and performance of a weaker / affected hand during bimanual interactions in functional / play based tasks with good reliability and validity . jebsen - taylor test of hand function ( jtthf ) : a standardized timed test measuring manual dexterity ( modified by eliminating the writing task ) with reliability and normative data reported for children . a three - minute limit was set for each task with a maximum overall score of 1080 seconds across the 6 tasks . the children 's hand experience questionnaire ( cheq ) : a 29-item questionnaire exploring independent participation and skilled use of an affected / hemiplegic hand in daily bimanual activities and reported competence and worry / confidence . aha : least detectable difference ( ldd ) was defined as ( 1.962sem ) and was equal to 5 points , representing a clinically meaningful difference for an individual using the rasch weighted log unit scores . raw scores are transformed into logits via rasch analysis to account for different degrees of difficulty of the items . logits are converted to a 0100  aha unit scale with higher scores representing better bimanual skills . . calculation of difference beyond 2 standard deviations of the normative data equated to 20% , representing a clinically meaningful difference . cheq : percentages of change relative to baseline in number of activities performed using 2 hands were calculated and change greater than 20% was considered meaningful . images were acquired on a 3 t ge scanner ( ge signa excite , milwaukee , wi , usa ) with training in a mock scanner prior to the first scan . the mri protocol included high resolution anatomical 3d fast spoiled gradient echo sequence ( fspgr ) ( slice thickness / gap = 1/0  mm ; field of view ( fov)/matrix : 240  mm/256  256 ; time to repeat ( tr)/time to echo ( te ) = 8.6/3.3  msec ) ; fmri performed with t2-weighted gradient echo echo - planar imaging ( ge - epi ) sequence ( slice thickness / gap = 3.5/0.3  mm ; fov / matrix = 240  mm/128  128 ; tr / te / flip angle = 2,250/29  msec/79 ) ; dti acquired along 19 diffusion gradient directions ( b = 1000  sec / mm ) and one with no applied diffusion gradient ( slice thickness / gap = 3/0  mm ; fov / matrix = 220  mm/128  128 ; tr / te = 11,000/91  msec ) . a block - design fmri motor task was used in which children clenched and extended all fingers of one hand in synchrony with 2 hz paced tones . there were 18 seconds of silence with one alert beep before the task began to let the children prepare for the motor task , followed by alternations between six epochs of rest , six epochs for right hand , and six epochs for left hand , each lasting 14 seconds . children were instructed to do their best to move only the affected or less affected hand in isolation . range of movement was limited to midrange by a soft plastic sponge ball placed in children 's palms . videos were recorded during the fmri task in order to assess the presence of mirror movements . mirror movements ( mm ) were subsequently rated according to the woods and teuber scale . on this scale , 0 indicates absence of mm , 1 = barely discernible , 2 = slight but sustained , 3 = strong and sustained , and 4 = movement equal to intended hand . fmri analysis was performed with brainvoyager qx 2 software package ( http://www.brainvoyager.com/ ) and was previously described . briefly , preprocessing included motion correction ( scans with head movement > 3  mm were rejected ) , high - frequency temporal filtering , and removal of low - frequency linear trends . the first six volumes were discarded to allow for stabilization of the signal ( to allow for t2 equilibration effects ) . the coregistered images were not transformed into a standard space but remained in each subject 's native space due to the substantial brain abnormalities in this population . fmri data sets from the 2 or 3 time points ( baseline , after intervention , and follow - up ) were coregistered to the 3d fspgr anatomic sequence of each participant from the baseline scan ( t1 ) to allow comparison between activations at the different time points . three - dimensional statistical parametric maps were calculated separately for each subject using a general linear model ( glm ) in which all stimuli conditions were positive predictors . two contrasts were studied : contrast 1 : affected hand versus baseline and contrast 2 : less affected hand versus baseline . we used the false discovery rate ( fdr ) procedures for the selection of thresholds , and the fdr ( q value ) chosen in the present study was 0.05 . two measurements were extracted.the peak activation in each region of interest ( roi ) was detected and a box - shaped volume of 25 voxels was placed around the peak of activation from which beta values were extracted . the beta weights were extracted separately from blocks that included movement of the hand contralateral to the lesion ( affected hand ) and of the hand ipsilateral to the lesion ( less affected hand ) . the selected roi beta weights refer to the fmri activation level and reflect the level in which each of the predictors explain the signal from the specified region . therefore , the beta weights characterize the level of task - related activity in each region selected.we also applied an additional quantitative measure of lateralization index ( li ) using the total number of activated voxels for each region of interest . for each roi , voxels were collected using all conditions and were compared with the baseline condition with a probability value less than 0.05 . li = ( contralateral  ipsilateral)/(contralateral + ipsilateral ) , where contralateral and ipsilateral equal the total number of voxels activated above threshold in areas around the central sulcus contralateral or ipsilateral to the moving hand . this approach yielded lis for the motor activation around the central sulcus that ranged from + 1 for unilateral activation pattern to 1 for ipsilateral activation pattern ( atypical ) , while values close to 0 reflect more bilateral activation patterns . the peak activation in each region of interest ( roi ) was detected and a box - shaped volume of 25 voxels was placed around the peak of activation from which beta values were extracted . the beta weights were extracted separately from blocks that included movement of the hand contralateral to the lesion ( affected hand ) and of the hand ipsilateral to the lesion ( less affected hand ) . the selected roi beta weights refer to the fmri activation level and reflect the level in which each of the predictors explain the signal from the specified region . therefore , the beta weights characterize the level of task - related activity in each region selected . we also applied an additional quantitative measure of lateralization index ( li ) using the total number of activated voxels for each region of interest . for each roi , voxels were collected using all conditions and were compared with the baseline condition with a probability value less than 0.05 . li = ( contralateral  ipsilateral)/(contralateral + ipsilateral ) , where contralateral and ipsilateral equal the total number of voxels activated above threshold in areas around the central sulcus contralateral or ipsilateral to the moving hand . this approach yielded lis for the motor activation around the central sulcus that ranged from + 1 for unilateral activation pattern to 1 for ipsilateral activation pattern ( atypical ) , while values close to 0 reflect more bilateral activation patterns . dti analysis was performed using dti studio software ( johns hopkins university , baltimore , md , usa ) as previously described . the diffusion tensor was first estimated on a voxel - by - voxel basis and axial diffusivity ( da ) , radial diffusivity ( dr ) , mean diffusivity ( md ) , and fractional anisotropy ( fa ) maps calculated . the corpus callosum ( cc ) and corticospinal tract ( cst ) were reconstructed using streamline fibre tracking with the fibre assignment by continuous tracking ( fact ) algorithm . fibre tracking was terminated when it reached a pixel with an fa value lower than 0.25 or when the turning angle was > 70. a single roi was used to extract the cc via a color coded midsagittal fa image [ 9 , 25 , 26 ] . further segmentation of the cc into genu , midbody , and splenium was performed based on the witelson parcellation scheme . a multiple roi approach was used to extract cst tracts , defining fibres that pass from the unilateral pons through the posterior limb of the internal capsule to the motor and premotor cortex . mean values of da , dr , md , and fa were calculated for each fibre . significant change in diffusivity parameters was defined as follows : changes above 5% were considered significant as previous studies reported changes around 5% following learning interventions , with smaller changes likely to reflect natural variation [ 28 , 29 ] . descriptive analysis was performed at a group level to compare the imaging parameters before and after intervention . improvement on behavioral tests was based on clinical significance as described in section 2.3 ( hand motor function assessment ) . for all imaging parameters ( beta values , li , and diffusivity values ) , mean percent change between pre- and post intervention imaging parameters was computed to assess the change between the different time points and baseline measures . pearson correlations were performed to study the association between the imaging parameters and manual function at the three time points . all statistical analyses were performed using spss ( chicago , il , usa , version 17.0 ) . the study group comprised 12 children ( 6 males ) aged 716 years ( mean 11  3.6  y ) , of which nine had right hemiparesis and the remainder had left hemiparesis . macs scores ranged from 1 to 3 , while gmfcs scores ranged from 1 to 2 . two children were born preterm and the rest at term . see table 1 for subject characteristics . overall , 11 out of 12 children improved behaviorally after intervention on at least 1 test , and eight children improved on two or more tests ( see table 2 ) . six out of eight children who were assessed at the third time point maintained improvement at follow - up . it should be noted that the one child who did not improve behaviorally participated in the magic habit camp in the previous year and appeared to experience a ceiling on his hand function progress . aha : 7 of 12 children improved significantly ( at least 5 points ) after intervention . of these , 3 maintained improvement at follow - up , and 1 further child showed significant improvement only at follow - up . cheq number of independent 2-handed activities : 6 of 12 children improved significantly ( at least 20% change ) after intervention . of these , 3 maintained improvement at follow - up , and 1 further child showed significant improvement only at follow - up . jtthf reaction time of the affected hand : 8 of 12 children improved significantly after intervention ( at least 20% change ) ; 4 children were unable to complete the task within the required time at both time points and thus were scored as not showing improvement . all of the 4 children with the additional assessment at time 3 who improved after intervention maintained the improvement at follow - up . at the group level , test scores improved after intervention on all tests , with the improvement tapering off at follow - up , apart from the jtthf where even greater improvement was seen at follow - up ( figures 2(a)2(c ) ) . mean increase in aha scores from pre- to post intervention was 5.13  4.09 points after intervention and 10.68  13.2 points by follow - up , while mean decrease in response time on the jtthf was 27.48%  36.44% after intervention and 33.6%  38.2% from baseline to 6-week follow - up . mean increase on the cheq 2-handed score was 5.58  7.4 points after intervention and 4.57  6.9 points at follow - up . overall , level of activation , as measured by beta values , increased after intervention and continued to increase at follow - up ( see figure 2(d ) ) . mean change in betas in the affected hemisphere when moving the affected hand ( contralateral ) , from pre- to post intervention was 26.14% increase ( n = 7 ) and from preintervention to follow - up was 34.75% increase ( n = 4 ) . in the less affected hemisphere , there was little change in level of activation ( ipsilateral to movement of the affected hand ) with mean change from pre- to post intervention of 2.4% ( n = 4 ) . one child ( subject 11 ) was rated as having significant mirror movements ( score of 3 on woods and teuber scale ) which might affect these values . yet , when excluding this child from the analysis , similar effects were detected with increase of 24% mean percent change from pre- to post intervention ( compared to 26.14% ) in the affected hemisphere when moving the affected hand and + 10% change in the less affected hemisphere when moving the affected hand ( compared to 2.4% ) . there was similarly little change in activation in the less affected hemisphere when moving the less affected hand ( contralateral ) of 1.5% ( n = 8) after intervention and 7.6% ( n = 5 ) change by follow - up . only one child had pre- and post intervention activation in the ipsilateral hemisphere when moving the less affected hand . the most severe case of hemiplegia ( case 6 ) , as represented by macs 3 , was the one child who did not respond behaviorally to the intervention . despite the absence of functional improvement , increases in brain activity as measured by beta levels during hand movement were seen . motor related activation was seen in the sensorimotor areas around the central sulcus and in the supplementary motor areas ( sma ) . in general , a shift to a unilateral activation after intervention was detected in some children when moving the affected hand . li when moving the less affected hand remained stable in all children except one ( subject 7 ) , who moved to a more unilateral pattern . of the 11 children who improved behaviorally , 4 showed improvements in li on movement of the affected hand , shifting towards a unilateral pattern , or maintained an originally unilateral pattern of activation ( subjects 1 , 2 , 4 , and 5 ) ( see table 3 ) . these improvements were maintained at follow - up ( except for 1 child who had no follow - up scan ) . one child showed improved li only at follow - up ( subject 6 ) . for three children , the li could not be calculated due to poor data quality of the fmri scan ( subjects 3 , 8 , and 12 ) . three children improved behaviorally yet did not have increased li after intervention , with some demonstrating a pattern of ipsilateral activation ( subjects 7 , 10 , and 11 ) . figure 3 shows a graphic presentation of activation in three children , before and after intervention . subjects 4 and 5 show a change towards unilateral activation after intervention , while only a slight change was evident in subject 6 . to test the hypothesis that the higher the li ( the more typical / unilateral the pattern of activation ) , the better the manual function , a correlation analysis between li and performance was conducted at the 3 time points . overall , the analysis showed that higher li values after intervention correlated with better manual skills . a borderline significant correlation ( r = 0.62 , p = 0.056 ) was detected between li before intervention and preintervention performance on the cheq and at post intervention this correlation was significant ( r = 0.686 , p = 0.041 ) ( see figure 4 ) . similar relationships were not evident between li and aha or jtthf at pre- and immediately post intervention . at follow - up , there was very little variance in li ( 4/5 children had values at or close to 1 ) hampering correlation analysis . therefore , we examined the correlation between li after intervention and manual function at follow - up , which enabled us to assess correlation after intervention , either immediately after or at follow - up . in this analysis , strong correlations were detected with all behavioural measures at follow - up : aha ( r = 0.820 , p = 0.046 ) , cheq ( r = 0.941 , p = 0.005 ) , and jthhf ( r = 0.814 , p = 0.049 ) ( see figure 4 ) . at the group level , no significant changes were detected for the md and fa values before and after intervention in the cc and in the affected and less affected cst . however , on an individual level , several children showed post intervention changes in dti values associated with improved wm integrity in the cc , affected , and less affected cst greater than those to be expected with natural variation ( see tables 4 and 5 ) . one child showed improvements in all segments of the cc . in the cst , 3 children showed improved diffusivity values on the affected side after intervention and 5 children on the less affected side . overall , both before and after intervention , increased wm integrity was related to better hand function . before intervention , significant correlations were detected between higher wm integrity in the genu and midbody of the cc and better baseline manual function . lower md in the genu and midbody was related to higher aha scores ( r = 0.58 , p = 0.05 ; r = 0.75 , p = 0.008 ; resp . ) . lower md and higher fa in the genu , midbody and splenium were related to better performance on the jtthf ( genu : fa r = 0.618 , p = 0.032 , midbody : md r = 0.668 , p = 0.025 , fa r = 0.675 , p = 0.023 ; splenium : md r = 0.578 , p = 0.049 ; resp . ) . higher wm integrity in both the affected and less affected cst was correlated with better unimanual function ( jtthf and fa in the less affected cst : r = 0.615 , p = 0.033 ; jtthf and affected cst : fa r = 0.667 , p = 0.035 ; md r = 0.664 , p = 0.036 ) . after intervention , higher wm integrity in the midbody of the cc ( reflected by low md and high fa ) was associated with better bimanual function ( aha : md : r = 0.815 , p = 0.004 ; fa : r = 0.670 , p = 0.034 ) and with better unimanual function ( jtthf : md : r = 0.772 , p = 0.009 ; fa : r = 0.687 , p = 0.028 ) . no significant correlations were detected between wm integrity and the cheq . at follow - up , fa in the genu of the cc was significantly correlated with aha ( fa : r = 0.85 , p = 0.03 ) and both fa and md with cheq 2 hands ( fa : r = 0.90 , p = 0.037 ; md : r = 0.93 , p = 0.007 ) . md and fa in the midbody of the cc were also correlated with aha ( md : r = 0.97 , p = 0.006 ; fa : r = 0.95 , p = 0.012 ) and jttjf ( md : r = 0.93 , p = 0.021 ; fa : r = 0.88 , p = 0.048 ) . no significant correlations were detected between wm integrity of the cst and manual function at either post intervention or follow - up . results from this study show changes in levels of activation , in pattern of lateralization , and in wm integrity following intervention . in addition , such changes were correlated with behavioral assessment at all three time points shedding light on possible pathways to explain how behavioral improvement following bimanual intervention is manifested in the brain . nevertheless , it is important to note that these changes were not detected in all ch regardless of the behavioral gains they showed . a main finding of this study is a shift towards a more unilateral activation pattern after intervention , reflected by higher li values . at the group level , abnormal pattern of brain activation was detected at baseline reflected by bilateral activation . in typically developing subjects , motor activation is primarily unilateral , being limited to the hemisphere contralateral to the hand in movement . following intervention , increased level of activation in the affected hemisphere was detected ( manifested by increased beta values ) in parallel with the shift in lateralization . these results are in line with a previous study that reported change in li towards unilateral pattern after cimt treatment in a small sample ( n = 4 ) . a recent systematic review also described several types of brain changes following therapy such as an increase in m1 excitability in subjects with ipsilesional reorganization and a decrease in m1 excitability in subjects with contralesional reorganization , indicating treatment - related plasticity . however , brain plasticity is a complex process and changes and varying etiologies , brain injury subtypes , or developmental experiences may have differential effects on neuroplastic changes following intervention . the association between li and manual function became stronger after the intervention with additional associations ( with both unimanual and bimanual functions ) emerging 6 weeks following intervention . yet , the improvement in li at follow - up was not matched by further behavioral improvements at this time . this may reflect the consolidation time of the newly learned skills ( plasticity processes ) enabling detectable expressions of relations between newly strengthened brain networks and more effective manual function by the end of treatment , and even more so at follow - up . indeed , children were encouraged to keep practicing their newly learned manual skills ; therefore , it may be that the plasticity processes continued during the six weeks enabling greater efficacy in more varied contexts . the finding that the associations between brain function and structure with behavior were more evident at follow - up may support the dynamical systems theory   which postulates that there is a period of instability evident in changing neural networks . from the motor perspective , there are different timescales in the characterization of changing behavior which is reflected in motor learning and development , demonstrated by different learning curves . nikolai bernstein 's theory of the  degrees of freedom  also relates to a period of enhanced variability in motor learning before the emergence of smooth dynamic motor control [ 33 , 34 ] . at the group level , no changes in wm integrity of large fibre tracts were seen following intervention , although more than half of the children showed significant change in at least one wm fibre tract in at least one diffusivity parameter . a threshold of 5% was chosen as a significant change based on several studies [ 28 , 29 ] . scholz et al .   reported on a 6-week juggling intervention in young adults and reported mean increases in fa after training in the order of 5% compared to baseline , with controls showing no significant change . similarly , a study of young adults learning a new language   reported up to 5% change in fa in learners versus controls over a 9-month learning period . changes in fa in language areas were 1 - 2% after 1 month , rising to 5% after 9 months ; however , controls also showed up to 3 - 4% change in fa , therefore limiting the reliability of the detected changes . it may be that dti , despite its sensitivity and important value in learning about wm integrity , is still too crude to measure subtle microstructural changes that may take place following a 2-week intervention . other diffusion based methods with higher spatial resolution and higher b value may be more sensitive to detect such changes . importantly relationships between wm integrity and manual functions emerged as a function of the intervention , and these relations remained significant and became stronger throughout the study period . mainly mean diffusivity in the midbody of the cc was associated with better bimanual ( aha ) and unimanual ( jtthf ) skills . md values in the midbody of the cc were correlated with the cheq at follow - up , and this association was not detected before intervention and was not yet evident directly after intervention . indeed the cheq , which reflects changes in bimanual function in daily activities , was previously reported to significantly improve after intervention . there are several methodological challenges when conducting imaging research in pediatric populations with some challenges specific to ch . there are often problems with data quality caused by excess movements , since children often find it difficult to remain still in the magnet . in addition , many children with ch exhibit additional comorbidities such as attention deficit hyperactivity disorder [ 36 , 37 ] . thus , scanning children , especially ch , requires a special set - up . in this study , we used a special set - up which included a practice session in a mock scanner ; the presence of the child 's guardian during all study stages including the mri scan ; and watching an animation movie of the child 's choice during the structural series of the scan . in the current study , we had to exclude only a few data sets due to motion artefacts , but in general the special set - up improved the children 's cooperation and data quality . an additional challenge is that children with movement difficulties frequently show associated head movements with the effort of moving their hands resulting in further motion artefact . furthermore , the phenomenon of mirror movements which are frequently observed in ch may influence fmri motor activation measurements . in our study , we recorded videos of the children when performing the motor task and retrospectively could identify mirror movements and take them into account during analysis . only one child demonstrated significant mirror movements and excluding him did not have a major influence . finally , there are methodological challenges in conducting longitudinal mri studies that quantitatively compare scans acquired at different times . there are many parameters that may affect the signal such as different level of head movement and different level of cooperation and grip force and parameters relating to the magnet . we tried to overcome these problems by using fdr for statistical analysis and by using the laterality index which provides a type of normalization of the fmri data . there are several limitations in this study , with some that are inherent to studies of ch . in this study , we had a relatively small sample size since it is difficult to recruit this population and since all children were enrolled to an intervention program which required attendance to a 2-week camp or adherence to a home - based programme . the heterogeneity of the sample due to the varied etiologies underlying ch may affect both the clinical motor features of the children and the type of brain pathology , making it difficult to find a general pattern of plasticity following intervention in this population . another limitation lies in the hand function assessments that may have impeded our ability to detect change . in particular , we noted a ceiling effect on the jtthf in which some capacity may have been demonstrated , but unless all items within each task were completed successfully ( e.g. , all 5 cards turned ) , a maximum time score of 1080 seconds was awarded and therefore not reflective of more discrete changes . in conclusion , changes in dti and fmri parameters were seen when comparing pre- and post intervention scans in ch following habit . brain plasticity varied in the study group with children showing different patterns of change after intervention . however , change towards a more unilateral brain activation pattern was consistently associated with motor improvements , thereby adding evidence of measurable neuroplasticity changes following bimanual intervention in children with hemiparesis .
neuroplasticity studies examining children with hemiparesis ( ch ) have focused predominantly on unilateral interventions . 
 ch also have bimanual coordination impairments with bimanual interventions showing benefits . 
 we explored neuroplasticity following hand - arm bimanual intensive therapy ( habit ) of 60 hours in twelve ch ( 6 females , mean age 11  3.6  y ) . 
 serial behavioral evaluations and mr imaging including diffusion tensor ( dti ) and functional ( fmri ) imaging were performed before , immediately after , and at 6-week follow - up . 
 manual skills were assessed repeatedly with the assisting hand assessment , children 's hand experience questionnaire , and jebsen - taylor test of hand function . 
 beta values , indicating the level of activation , and lateralization index ( li ) , indicating the pattern of brain activation , were computed from fmri . 
 white matter integrity of major fibers was assessed using dti . 
 11/12 children showed improvement after intervention in at least one measure , with 8/12 improving on two or more tests . 
 changes were retained in 6/8 children at follow - up . 
 beta activation in the affected hemisphere increased at follow - up , and li increased both after intervention and at follow - up . 
 correlations between li and motor function emerged after intervention . 
 increased white matter integrity was detected in the corpus callosum and corticospinal tract after intervention in about half of the participants . 
 results provide first evidence for neuroplasticity changes following bimanual intervention in ch .