Projections of two separate cortical areas for rhythmical jaw movements in the rat

The cortico-bulbar projection from two separate cortical areas which induce different types of rhythmical jaw movements (RJM), and the relationship between these cortical areas were studied with horseradish peroxidase tracing method. One area (A-area) corresponded to the primary jaw motor area and the other (P-area) was located in the agranular insular cortex. Separate descending pathways from two areas passed through the pyramidal tract and projected to the supratrigeminal nucleus, the intertrigeminal region, the dorsal part of the trigeminal sensory complex, and the reticular formation. In the reticular formation, the A-area projected more medially than the P-area did, and the ipsilateral projection from the P-area was more prominent than that from the A-area, although contralateral projections were dominant in the majority of regions. The two areas had only a sparse reciprocal connection. We suppose that the difference in patterns of RJM induced by the two cortical RJM areas may be due to the different projection patterns from these two areas.