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 magnetoencephalography (MEG). We measured somatosensory evoked magnetic fields (SEFs) to median nerve stimulation with a 122-channel helmet-shaped magnetometer in 10 healthy subjects. In five, the magnetic field patterns suggested long-latency activation of the ipsilateral SMI. Source locations 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 suppression of these responses during movement of the contralateral fingers. Sensory input to ipsilateral SMI could play a role in sensorimotor integration of bilateral movements.