Magnetoencephalographic investigation of somatosensory homunculus in patients with peri-Rolandic tumors

In order to investigate functional topography of the hand somatosensory cor tex in five patients with periRolandic tumors (four frontal lobes and one p arietal lobe), we recorded somatosensory evoked fields (SEFs) using magneto encephalography (MEG) after stimulation of the median nerve (MN) and the fi ve digits. The results obtained were compared with those of five normal hea lthy subjects. In all five patients, SEFs following MN and digit stimulatio n showed the previously described respective N20m and N22m components of pr imary sensory response. Single dipole modeling was applied to determine the three dimensional cortical representations of the N20m and N22m components . The cortical representations of the hand were identical to those of norma l subjects, arranging in an orderly somatotopic way from lateral inferior t o medial superior in the sequence thumb, MN, index, middle, ring, and littl e fingers. This sensory homunculus was confirmed by cortical recording of t he somatosensory evoked potentials (SEPs) at the time of surgery. Thus, we demonstrate that SEFs, recorded on MEG in conjunction with source localizat ion techniques, are useful to non-invasively investigate the functional top ography of the human hand somatosensory cortex in pathological conditions.