Brain stimulation-induced changes of phonation in the squirrel monkey.

In 11 squirrel monkeys (Saimiri sciureus), the brain stem was systematically explored with electrical brain stimulation for sites affecting the acoustic structure of ongoing vocalization. Vocalization was elicited by electrical stimulation of different brain structures. A severe deterioration of the acoustical structure of vocalization was obtained during stimulation of the caudoventral part of the periaqueductal grey, lateral parabrachial area, cortico-bulbar tract, nucl. ambiguus and surrounding reticular formation, facial nucleus, hypoglossal nucleus, solitary tract nucleus and along the fibres crossing the midline at the level of the hypoglossal nucleus. It is suggested that these structures are part of, or at least have direct access to, the motor coordination mechanism of phonation. Complete inhibition of phonation was obtained from the raphe and raphe-near reticular formation.