Magnetic brainstem stimulation of the hypoglossal nerve in normal subjects

Electrophysiological evaluation of motor pathways to the lingual muscles is technically challenging. Previous studies utilizing transcranial magnetic stimulation (TMS) of the parieto-occipital region with a round coil reported difficulties in eliciting tongue motor responses. In this study, we utilized TMS with a double cone coil at the posterior head region to obtain tongue motor evoked potentials. Our findings suggest activation at or distal to the hypoglossal nuclear level, but proximal to the hypoglossal canal region. Our method can be usefully applied in future studies of brainstem and cranial nerve function.