Neuronal activity in the medulla oblongata during vocalization. A single-unit recording study in the squirrel monkey

In six squirrel monkeys (Saimiri sciureus), the medulla oblongata was explo red with microelectrodes, looking for vocalization-correlated activity. The vocalizations were elicited by microinjections of glutamate agonists into the periaqueductal grey of the midbrain. Vocalization-related cells were fo und in greater numbers in the nucl. ambiguus (Ab) and retroambiguus (RAb), in the parvocellular, magnocellular and central reticular formation as well as in the solitary tract nucleus and spinal trigeminal nucleus. Small numb ers were also found in the vestibular complex, cuneate nuclei, inferior oli ve and lateral reticular nucleus. A differentiation of the neuronal respons es into 12 reaction types reveals that the frequency of each reaction type varies from brain structure to brain structure, thus allowing a specificati on of the different vocalization-related areas. According to this specifica tion, it is proposed that initiation of vocalization takes place via the pa rvocellular reticular formation; vocal pattern control is mainly brought ab out by the parvocellular reticular formation, Ab, solitary tract nucleus an d spinal trigeminal nucleus; expiratory control and respiratory-laryngeal c oordination is carried out by the RAb, Ab and central nucleus of the reticu lar formation; vocalization-specific postural adjustments are carried out v ia the vestibular and cuneate nuclei. (C) 2000 Elsevier Science B.V. All ri ghts reserved.