Somatosensory-evoked fields for gingiva, lip, and tongue.

To localize the oral primary somatosensory cortex, we measured somatosensory-evoked fields for the lip, gingiva, and tongue in six healthy subjects. The latency of the first peak of the posterior-oriented current in the contralateral hemisphere was 50.9 +/- 8.3 ms for the gingiva, significantly shorter than those for the lip and tongue peaks. The equivalent current dipole was localized on the central sulcus. The gingival dipole was localized significantly inferior to the lip dipole but not different from the tongue dipole. The moment of the gingival dipole was significantly smaller than that of the lip dipole but not different from that of the tongue dipole. Differences in the above parameters were negligible between the left and right, anterior and posterior, and upper and lower locations within the same organ, except that the dipole location for the anterior upper tongue was significantly inferior to that for the lower tongue.