Neurobiology of primate audio-vocal behavior

Audio-vocal behavior is an outstanding means of social communication among nonhuman primates and man. Neurobiological studies of this behavior contribute to a better understanding of communication processes in general and of the cerebral prerequisits for the evolution of language and speech in particular. In the first part of the review the cerebral system which generates, selects and controls species-specific vocal behavior is described in anatomical and physiological terms. Its structures and functions are organized in a hierarchical manner whereby the pericingular cortex and the periaqueductal gray are nodal areas in the system. In the second part auditory decoding mechanisms of vocal signals are discussed in terms of cortical ablation studies and response characteristics of single neurons along the auditory pathway. There are marked differences in the processing of natural calls at the collicular, medial geniculate and cortical levels. The cortex makes a necessary contribution to the decoding of complex sounds. References to the problem of lateralization of auditory function in non-human primates are made. A keystone for the understanding of communication processes in general lies in the question of how the signal producing motor system and the signal receiving decoding system is centrally tied together. One way to investigate such processes is to compare single unit responses along the auditory pathway during an animal's own phonation and during the playback of that vocalization. The results provide evidence for an internal feed-forward mechanism during phonation which influences parts of the auditory system.