Chapter 8.1 - Role of the periaqueductal gray in expressing vocalization

Abstract

Abstract In this chapter, the current knowledge about the role of the midbrain periaqueductal gray (PAG) in the expression of vocalization is reviewed. Electrical and pharmacological stimulation of the PAG evokes species-specific calls with short latency and low habituation in many mammals. Lesion studies show that the destruction of the PAG and lateral bordering tegmentum can cause mutism without other motor impairments. Neuroanatomical studies revealed that vocalization-eliciting regions of the PAG receive a widespread input from all brain regions, reaching from the forebrain to lower brainstem areas. On the other hand, the vocalization-controlling PAG projects into intermediate and premotor neuron regions of the brainstem recently identified as the vocal pattern generator. Finally, neurophysiological data suggest that vocalization-correlated activity of PAG neurons that initiates specific call types, and sometimes even shows characteristics of an audio-vocal interface region, does not reflect the acoustical structure of a particular call type. It is proposed that the PAG is not involved in direct vocal motor coordination and pattern generation, but rather has a triggering/gating function. It seems to be responsible for the initiation and control of intensity of vocal responses by integrating various inputs, including cognitive, motivational, sensory, motor and arousal-controlling components, and transmitting that information to the vocal pattern generating areas within the lower brainstem.