Dual brain stem projection from the cortical masticatory area in guinea-pig

The cortical masticatory area (CMA) in the guinea pig is subdivided into the anterior and posterior parts (A-CMA and P-CMA), based on the pattern of the CMA-induced rhythmical digastric EMG burst and the cytoarchitecture. The anterograde tracing of horseradish peroxidase from the A-CMA and P-CMA revealed, in addition to a common projection to the region around the trigeminal motor nucleus and the parvicellular reticular formation bilaterally, a massive projection to the ipsilateral superior colliculus (SC) from the A-CMA but not from the P-CMA. The results suggest a dual brain stem projection system from the CMA: the direct pyramidal route from the P-CMA and the SC-mediated indirect route from the A-CMA.