THE COURSE OF CORTICO-HYPOGLOSSAL PROJECTIONS IN THE HUMAN BRAIN-STEM- FUNCTIONAL TESTING USING TRANSCRANIAL MAGNETIC STIMULATION

Cortico-hypoglossal projections were investigated in II patients with unifocal ischaemic lesions of different brainstem levels using transcr anial magnetic stimulation. Lesion topography was documented by MRI st udies. In seven patients rite projections to the ipsi- and contralater al hypoglossal nuclei were separately affected. Pontine lesions at the ventral paramedian base close to the midline affect the contralateral pi-ejections while lateral lesions at the pontine base affect the ips ilateral projections. Lesions of the paramedian dorsal pontine base do not involve the cortico-hypoglossal projections. Our findings indicat e that the cortico-hypoglossal fibres branch off the main ventral pyra midal tract. Lesions of the dorso- and mediolateral menulla impair onl y the ipsilateral projections. We conclude that ipsilateral projection s enter the hypoglossal nucleus from its lateral aspect and that the c ontralateral projections cross the midline at the pontomedullary junct ion.