Representation of pattern of cortically-induced jaw movements in the unanesthetized guinea pig

Abstract

Repetitive electrical stimulation to the cortical masticatory area (CMA) evokes rhythmic jaw movements in various species. Patterns of cortically induced rhythmic jaw movement (CIRJM) vary depending on the stimulation site. The aim of this study is to clarify the representation of pattern of CIRJMs in the unanesthetized guinea pig, in which the masticatory muscle EMG activities and the jaw movements were recorded. CIRJMs were evoked from the granular cortex lateral to the agranular cortex, which has been defined as the face MI. CIRJMs were classified into four types on the basis of jaw movement pattern: small (type A) and large (type B) vertical movement, as well as movement with large lateral shift unilaterally (type C) and bilaterally (type D). Types A and B were characterized by small amplitude of masseter activities, not similar to typical jaw movements of mastication. Types C and D were characterized by large activities in the unilateral and bilateral masseter muscle, respectively. Type C was similar to the unilateral jaw movements during chewing in natural mastication, while type D was similar to bilateral jaw movements. Types A and B were evoked from the focal area in the CMA medial to the area inducing types C and D. These results suggest that the CMA of the guinea pig may be divided into two parts with different function. [J Physiol Sci. 2007;57 Suppl:S160]