TACTILE INFORMATION FROM THE HUMAN HAND REACHES THE IPSILATERAL PRIMARY SOMATOSENSORY CORTEX

Neuromagnetic responses to median nerve stimulation were studied in si x healthy right-handed subjects. In the rest condition, only the right and left median nerves were alternately stimulated at the wrists. In two other conditions, continuous superficial tactile stimulation was c oncurrently applied to either the left pr right hand. Tactile stimulat ion of palm and fingers of one hand enhanced, in the ipsilateral prima ry somatosensory cortex (SI), responses to median nerve stimulation of the other hand. This effect was stronger in the left than the right S I, Our data provide evidence in humans for the access of cutaneous inf ormation from the hands to ipsilateral SI, probably via excitatory tra nscallosal pathways. This interhemispheric information transfer may re present a neurophysiological substrate of somatosensory fusion between the hands.