Non-transcallosal ipsilateral area 3b responses to median nerve stimulus.

We report two patients with left hemisphere lesions who had no normal left hemispheric responses to right median nerve stimulus on magnetoencephalography but displayed right area 3b responses. One patient had suffered a severe left hemispheric contusion and the other left hemispheric infarction. Equivalent current dipoles of these ipsilateral responses were detected on the central sulcus adjacent to the location of the N20m response to left median nerve stimulus. The somatosensory afferent pathway from the hand may extend directly to the ipsilateral area 3b without following the transcallosal pathway in at least part of the population.