Late pain-related magnetic fields and electric potentials evoked by intracutaneous electric finger stimulation.

Surface magnetic and electric recordings were used to localize the sources of late pain-related magnetic fields and electric potentials, evoked by painful intracutaneous electric finger stimulation. We find that the source of the P90m component of the evoked magnetic field lies in the finger area of the primary somatosensory cortex; the sources of the N150m and P250m are found to reside in the frontal operculum. These findings are unexpected from the evoked electric potential data, which suggest a central location for these sources. We also note that the interpretation of the electric data was confounded by the presence of an alpha-like oscillation, which overlapped many components of the evoked potential.