Somatosensory-evoked Fields for Gingiva, Lip, and Tongue

Abstract

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.

Neuromagnetic Evidence that Gingiva Area is Adjacent to Tongue Area in Human Primary Somatosensory Cortex

“…The present study found that the lip ECD was located higher than the tongue ECD of the SEFs, corresponding to the previous findings by cortical stimulation (Penfield and Boldrey 1937;Penfield and Rasmussen 1950), cortical recording of somatosensory potentials (McCarthy et al 1993), and SEFs (Yamashita et al 1999;Nakahara et al 2004). However, we found no statistical difference between the ECDs of the buccal gingiva, lingual gingiva, and tongue, in contrast to the previous conclusion by Penfield and colleagues (Penfield and Rasmussen 1950) that gingival SI is located higher than tongue SI, but which was based on complicated results.…”

“…However, only the lingual side of the gingiva was stimulated in our previous study, so the location of the SI cortices of the buccal and lingual gingiva areas might be different. The present study extended our previous investigation (Nakahara et al 2004) by adding stimulation points including the buccal side of the gingiva to delineate the fine SI somatotopy of the gingiva area.…”

“…SEFs were measured by electrical stimulation of the lip, buccal gingiva, lingual gingiva, and tongue using our homemade clip electrode used in our previous studies Nakahara et al 2004). A total of eight points were stimulated for each oral structure: left and right; anterior (near the lateral incisor) and posterior (near the first molar); and upper and lower parts.…”

“…This study accepted only ECDs accounting for > 90% of the field variance and with confidence volume < 1 cm 3 . The single-ECD assumption is well known to account for the peak signals in previous MEG studies of SI response (Karhu et al 1991;Hari et al 1993;Kakigi 1994;Kawamura et al 1996;Nakasato et al 1996;Ohtomo et al 1996;Iwasaki et al 2001;Nagamatsu et al 2001;Nakahara et al 2004). Therefore, we used the single-ECD model for the hemispheric data contralateral to the stimulus side.…”

“…Recently, we compared the somatosensory evoked fields (SEFs) for gingiva, lip, and tongue in six healthy subjects and found that the gingival equivalent current dipole (ECD) was localized significantly inferior to the lip ECD but not different to the tongue ECD (Nakahara et al 2004). This observation may conflict with the previous studies by Penfield and colleagues (Penfield and Boldrey 1937;Penfield and Rasmussen 1950).…”