Somatic motor and sensory representation in the cerebral cortex of man as studied by magnetoencephalography and transcranial magnetic stimulation.

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PurposePenfield reported cortical maps of sensory and motor representation in human brain. In these maps, most of body parts faced each other across central sulcus, but only neck was located separately in motor and sensory cortex, i.e. between finger and face in motor cortex and medial to finger in sensory cortex. We thought that this fact was associated with mechanism of focal dystonia, such as spasmodic torticollis, and sensory trick. As the first step to elucidate such a clinical question, we evaluated motor and sensory cortex of finger, face and neck by magnetoencephalography (MEG) and transcranial magnetic stimulation (TMS). The MEG and TMS are new devices that can evaluate human brain function noninvasively.A TMS studyFive healthy subjects were participated. We evaluated the locations of their motor area of finger, face and neck used by one-divisional mapping of TMS. We recorded motor evoked potentials (MEPs) of subjects from first dorsal interosseis (finger), musculus orbicularis oris (face) and sternocleidomastoideus (neck). As a result, the finger and face area of motor cortex were located in about 5cm and 9cm lateral from vertex respectively, while the neck area was exist in about both 3cm and 7cm lateral to vertex, separately. Our results suggested that the neck area of motor cortex existed near the trunk area which faced the neck and trunk area of sensory cortex, as well as between finger and face area which reported by Penfield.A MEG studySomatosensory evoked magneticfields (SEF) were recorded in ten healthy subjects following to electrical stimulation of median nerve at wrist, skin of finger and motor point of thenar muscle. There were four peaks of SEF at about 20ms, 30ms, 40ms and 60ms after median nerve stimulation, two peaks at about 20ms and 30ms after finger stimulation, and a peak at about 60ms. The equivalent current dipoles of these peaks were all near the hand area of the primary sensory cortex.