(Re-)organization of basal ganglia in congenital hemiparesis with ipsilateral cortico-spinal projections.

In congenital hemiparesis after pre- or perinatally acquired unilateral brain lesions, many patients control their paretic hand via ipsilateral cortico-spinal projections from the contralesional hemisphere. In order to clarify the pattern of basal ganglia activation in case of such a shift of the primary motor cortical representation (M1) of the paretic hand to the contralesional hemisphere, fMRI was performed in eight patients with congenital hemiparesis due to unilateral periventricular white matter lesions and ipsilateral corticospinal projections to the paretic hand (as determined by focal transcranial magnetic stimulation). FMRI during active movements of the paretic hand yielded basal ganglia activation in the ipsilateral (=contralesional) hemisphere, but not in the contralateral (lesioned) hemisphere. Thus, (re-)organization in congenital hemiparesis with ipsilateral cortico-spinal projections includes, in addition to the ipsilateral primary motor cortex (M1), also the ipsilateral basal ganglia - in contrast to the primary somatosensory cortex (S1), which is typically preserved in the affected hemisphere.