MODULATION OF SOMATOSENSORY-EVOKED MAGNETIC-FIELDS BY SENSORY AND MOTOR INTERFERENCES

MODULATORY influences of skilled exploratory finger movements on somat osensory evoked magnetic fields evoked by median nerve stimulation wer e investigated in six healthy subjects using a whole head magnetometer (MEG) system. The exploratory finger movements caused major changes i n the somatosensory evoked fields. The most prominent effect was a rev ersal of the dipolar magnetic field around 30 ms after median nerve st imulation. Similar but less pronounced effects were exerted by repetit ive finger movements and tactile stimulation of the hand. A dipole ana lysis and super-imposition of resulting sources on individual MRI scan s showed that all somatosensory evoked fields up to 60 ms after stimul ation, and the modulation of these responses were located in the prima ry somatosensory cortex (SI).