Common input of the cranial motor nuclei involved in phonation in squirrel monkey.

Our aim was to locate brain regions projecting to all cranial motor nuclei involved in phonation simultaneously, that is, the ambiguus, trigeminal motor, facial, and hypoglossal nuclei. For this purpose, four squirrel monkeys (Saimiri sciureus) were injected with horseradish peroxidase, each of the four nuclei in a different animal. Those regions retrogradely labeled in all four cases then were injected in another 29 animals with [3H]leucine for anterograde tracing. We found that the only region connected directly with all phonatory motor nuclei is a restricted portion of the pontine and medullary reticular formation, including the nucl. subceruleus ventralis, nucl. parvocellularis and nucl. centralis myelencephali. It is assumed that these nuclei are involved in the integration of vocal fold adduction, articulation, and respiration during vocal utterances.