ACTIVATION OF IPSILATERAL PRIMARY SENSORIMOTOR CORTEX BY MEDIAN NERVE-STIMULATION

WE report evidence for activation of ipsilateral primary sensorimotor cortex (SMI) after median nerve stimulation recorded with magnetoencep halography (MEG). We measured somatosensory evoked magnetic fields (SE Fs) to median nerve stimulation with a 122-channel helmet-shaped magne tometer in 10 healthy subjects. In five, the magnetic field patterns s uggested long-latency activation of the ipsilateral SMI. Source locati ons found by current dipole fitting corresponded to the SMI hand area, as determined by contralateral stimulation. Further evidence for the origin of the ipsilateral responses in SMI was provided by the suppres sion of these responses during movement of the contralateral fingers. Sensory input to ipsilateral SMI could play a role in sensorimotor int egration of bilateral movements.