Differences in sensory and motor cortical organization following brain injury early in life

There have been a number of physiological studies of motor recovery in hemi plegic cerebral palsy which have identified the presence of novel ipsilater al projections from the undamaged hemisphere to the affected hand. However, little is known regarding the afferent projection to sensory cortex and it s relationship to the reorganized cortical motor output. We used transcrani al magnetic stimulation (TMS) to investigate the corticomotor projection to the affected and unaffected hands in a group of subjects with hemiplegic c erebral palsy, and also performed functional magnetic resonance imaging (fM RI) studies of the patterns of activation in cortical motor and sensory are as following active and passive movement of the hands. Both TMS and fMRI de monstrated a normal contralateral motor and sensory projection between the unaffected hand and the cerebral hemisphere. However, in the case of the af fected hand, the TMS results indicated either a purely ipsilateral projecti on or a bilateral projection in which the ipsilateral pathway had the lower motor threshold, whereas passive movement resulted in fMRI activation in t he contralateral hemisphere. These results demonstrate that there is a sign ificant fast-conducting corticomotor projection to the affected hand from t he ipsilateral hemisphere in this group of subjects, but that the predomina nt afferent projection from the hand is still directed to the affected cont ralateral hemisphere, resulting in an interhemispheric dissociation between afferent kinesthetic inputs and efferent corticomotor output. The findings indicate that there can be differences in the organization of sensory and motor pathways in cerebral palsy, and suggest that some of the residual mot or dysfunction experienced by these subjects could be due to an impairment of sensorimotor integration at cortical level as a result of reorganization in the motor system.