Functional relevance of ipsilateral motor activation in congenital hemiparesis as tested by fMRI-navigated TMS

Many, but not all patients with congenital hemiparesis (i.e., hemiparesis due to a pre-, peri- or neonatally acquired brain lesion) control their paretic hands via ipsilateral cortico-spinal projections from the contra-lesional hemisphere (CON-H). Patients who still control their paretic hands via preserved crossed cortico-spinal projections from the damaged hemisphere nevertheless show increased fMRI activation during paretic hand movements in the CON-H. We used fMRI-navigated rTMS induced functional lesions over the primary motor cortex (M1) hand area, the dorsal premotor cortex (dPMC) and the superior parietal lobe (SPL) of the CON-H in four of these patients to investigate whether this increased ipsilateral activation during finger movements of the paretic hand contributes to movement performance. Functional lesions of the dPMC and M1 but not SPL of the CON-H induced decreased temporal preciseness of finger sequences. The present results argue for a possible role of dPMC and M1 of the CON-H on complex motor behavior even in those patients with congenital hemiparesis who control their paretic hands via crossed cortico-spinal projections from the damaged hemisphere.