Abstract
The measurement of somatosensory evoked magnetic fields (SEFs) perpendicular to the scalp over 25 positions was carried out in a nonmagnetically shielded room with a SQUID connected to a second order gradiometer. The tibial nerve of the right ankle was stimulated electrically. SEFs were averaged by 500 measurements at one position with a bandpass filter of 1 to 30Hz. Isofield contour maps for middle and/or long latencies of 75 to 115ms rotated lockwisely on the mesial surface of the scalp representing dipolar and/or dipole-like pattern. To trace the equivalent source localization in the cortex, we calculated, the equivalent current dipole (ECD) in a meaning of the best fit between experimental and theoretical distribution. The calculated ECDs for these latencies were in the range of 19.7mm to 24.1mm as the depth from the scalp. To confirm the validity of the location of ECDs in the cortex, these results were inserted MR head imagings of the subject. As the results, these were concentrated at the postcentral gyrus of the contrary side to timulation site and were in a good agreement with a viewing point of the sensory foot representation area to the functional localization of the brain.
