The neural control of vocalization in mammals: a review

The review describes a model of vocal control, based mainly on research in the squirrel monkey, which consists of two hierarchically organized pathways. One runs from the anterior cingulate cortex via the periaqueductal gray (PAG) into the reticular formation of pons and medulla oblongata, and from there to the phonatory motoneurons. This pathway controls the readiness to vocalize. Although the anterior cingulate cortex in this pathway plays a role in voluntary initiation of vocal behavior, the PAG is involved in vocal gating at a more elementary level. The second pathway runs from the motor cortex via the reticular formation to the phonatory motoneurons and includes two feedback loops providing the motor cortex with preprocessed information needed by the latter to generate the final motor commands. One of these feedback loops involves the basal ganglia and the other the cerebellum. The motor cortex together with its feedback loops is involved in the production of learned vocal patterns. These structures seem to be dispensable, however, for the production of innate vocal patterns, such as the nonverbal emotional vocal utterances of humans and most nonhuman mammalian vocalizations. These innate vocal patterns seem to be generated in the pontine and medullary reticular formation.