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Localization of Palatal Area in Human Somatosensory Cortex

¹ Oral Health Science Center, Department of Oral and Maxillofacial Surgery,
² Department of Physiology,
³ Laboratory of Brain Research, and
⁴ Department of Oral and Maxillofacial Implantology, Tokyo Dental College, 1-2-2, Masago, Mihama-ku, Chiba 261-8502, Japan

View larger version (26K): [in this window] [in a new window]   Figure 1. Measurement of somatosensory-evoked magnetic fields for the hard palate. (A) Anatomical diagrams showing 3 stimulation sites for the palate. (B,C) The Ag-AgCl electrodes (approximately 2.5 mm between electrodes) were embedded in a custom-made plastic splint attached to the maxillary dentition to obtain a fixed stimulus position. (D) Typical examples of whole-scalp magnetic responses of somatosensory-evoked magnetic fields following stimulation of the right first transverse palatine ridge. Traces are plotted on the "flattened head", as viewed from above with the person’s nose upwards. Each trace began 100 msec prior to and ended 300 msec after stimulus onset. Circles indicate channels showing prominent magnetic signals. (E) Enlarged superimposed traces of the somatosensory-evoked magnetic field evoked by right-side stimulation of the first (upper) and third transverse palatine ridges (middle), and the greater palatine foramen (lower). The 3 successive identifiable peak signal components were designated 1M, 2M, and 3M.

View larger version (41K): [in this window] [in a new window]   Figure 2. Source locations. (A–C) Magnetic resonance images showing the locations of equivalent current dipoles of the 1M, 2M, and 3M components following electrical stimulation of the first transverse palatine ridge (A), the third transverse palatine ridge (B), and the greater palatine foramen (C). Blue circles show the locations of equivalent current dipoles on frontal planes of magnetic resonance images. The equivalent current dipoles of 1M (left images) and 2M (middle images) are located in the post-central gyrus, and those of 3M (right images) are located in the upper bank of the Sylvian fissure. (D) Locations of contralateral equivalent current dipoles of 1M were superimposed on the three-dimensionally reconstructed magnetic resonance image of the individual’s brain. Solid lines indicate the central sulcus, the Sylvian fissure, and the great longitudinal fissure.

View larger version (20K): [in this window] [in a new window]   Figure 3. Averaged equivalent current dipole positions. (A,C) Comparisons of the three-dimensional equivalent current dipole locations on each axis between 3 regions of the hard palate and median nerve stimulations are shown for 1M (A) and 2M (C) components. Somatosensory representation of palatal mucosa in the primary somatosensory cortex shows anterior and inferior orientations in the primary somatosensory cortex, compared with representation of the hand area. (B,D) Distances of equivalent current dipoles from each site on the palate to the median nerve are shown for 1M (B) and 2M (D). Each site for the palatal area in the primary somatosensory cortex was localized contiguously. Statistically significant differences are labeled with asterisks (P < 0.05).