Changes in masticatory movements and motor neuronal activities after lesioning of the tongue projection area of the first somatosensory cortex in awake cats.

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We have studied activity patterns and properties of mastication-related neurons (MRNs) in the orofacial first somatosensory (Sl) and motor (MC : M,P and C) cortices of awake cats. Most MRNs in Sl, M,P and C Had common receptive fields in perioral or tongue regions. Over 90% of MRNs in Sl showed activity changes following the masticatory rhythm (Post-movement RB). Over 50% of MRNs in M showed sustained activities (Pre-movement SB) before and during masticatory movements. About 40% of MRNs in P showed activity changes before movements of the jaw and tongue (Pre-movement TB). About 50% of MRNs in C were Post-movement RB.To investigated the function of the perioral or tongue projection area of Sl, we examined changes in orofacial behaviors and activities of MRNs in MC for 5-6 weeks after lesioning by a kainic acid injection (0.1%, 2mul) into the perioral or tongue projection area (PL and TL-cats). In the early phase (for 10 days after a lesion), PL-cats showed a delay in the masticatory start and a drop of food from mouth. TL-cats showed prolongations of the ingestion time. The proportion of MRNs with receptive fields in the perioral region of PL-cats was reduced by 70% in M,P and C in comparison with norma cats. MRNs with receprive fields in the tongue of TL-cats were not recorded in P.PL-cats decreased Pre-movement SB rate in M and Post-movement RB rate in C.TL-cats decreased Pre-movement TB rate in P.These findings suggest that perioral or tongue information in Sl during mastication may transfer commands of continuous contractions around the mouth or of appropriate movements following food condition to M or P.