A study of the central control of vocalization using the squirrel monkey.

In the squirrel monkey (Saimiri sciureus), the electrical activity of single neurones was compared in the periaqueductal grey of the midbrain and the reticular formation of the medulla oblongata during vocalization, using a recently developed telemetric technique. The results show that both structures contain neurones with vocalization-correlated activity. There are characteristic differences between the two structures, however. Neurones showing changes in discharge rate with changes in fundamental frequency were only found in the reticular formation, whereas neurones firing immediately before vocalization, but not during vocalization, were almost exclusively found in the periaqueductal grey. It is concluded that the reticular formation is involved in vocal motor coordination, while the periaqueductal grey mainly serves gating functions.