Analysis of Jaw Movements from the Cortical Jaw Motor Area and Amygdala

Abstract

Since the studies of FRITSCH and HITZIG in 18701) there have been many reports on the cortical localization of the motor area of jaw, and it has been confirmed that this motor area is localized in the frontotemporal parts of the cortex in various animals. However, there are yet many questionable points on such details as the neural course from the cortex to the motor nucleus of the fifth cranial nerve. For instance, SHERRINGTON2) reported that the jaw motor area of the cortex controls the contralateral jaw muscles, while MILLER3) emphasized the ipsilateral projection. In addition, MAGOUN et al.4) detected the following facts: Rhythmic movements of chewing arise from the medial portion of the rostral end of the anterior sylvian gyrus in the cat, and the corticofugal pathway for mastication may be followed up from the cortex in the internal capsule and basis peduncli to the extreme caudal end of the pons, without any relay station and with no decussation in this pathway. On the other hand, HIRAYAMA5) claimed that the jaw motor area of the dog was localized in the lower parts of the precentral gyrus, the neural pathway from here to the bulbar trigeminal motor nucleus changing its neuron in the ipsilateral thalamus and after that it decussated in the midbrain. Recently, many works have been done on the physiologic function of the limbic system of the brain by neurophysiologists6-14), and especially the feeding or alimentary function of the amygdala and hypothalamus has been disclosed. Therefore it is very important to understand the physiologic relation of the cortical jaw motor area and function of the amygdaloid nucleus. Besides, there are various patterns of jaw movements, i.e., jaw opening, jaw closing, protrusion and retraction, and so on, neural mechanisms of which have not yet been studied. In this experiment the jaw movements induced by electrical stimulation of the cortex, amygdala and other various brain structures were analyzed precisely and the functional relations between these brain structures on jaw movements are discussed. The descending pathways of the jaw movement from the cortical jaw motor area and amygdaloid nucleus were determined by the evoked electromyographic method in another experiment, which will be published successively. © 1960, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.