Serial N20m dipoles in somatosensory evoked magnetic fields move along the distal-proximal representation of the digit area 3b of the human cortex.

We studied the relationship between the distal-proximal representation of the digit in area 3b and moving dipoles of the primary magnetic response (N20m). By the use of ring electrodes, a distal or proximal portion of the middle finger was stimulated to elicit N20m. The dipole locations were sequentially analyzed around the N20m peak. The dipole locations did not differ between distal and proximal stimulation before the N20m peak. After 0.4 ms post-N20m peak, however, the dipoles following proximal stimulation substantially and progressively shifted laterally to those following distal stimulation. The result suggests that the N20m dipole moves from the distal representation toward the proximal representation of the digits in area 3b.