Cortical control for mastication in cats: changes in masticatory movements following lesions in the masticatory cortex.

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.