The Mechanisms of Motor Programming for Learned Vocalization in Songbirds

Vocal signals, the fundamental interface for communication, convey information in their acoustic and temporal structures. Neural systems must extract the information from complex sequences of sound elements and, in turn, generate the motor commands for vocal sequences. Because humans acquire vocal communication after birth, the neural systems must establish a precise correspondence between sensory and motor representations of the vocal signals and control vocal behavior under the guidance of auditory information [1]. Recent advances in noninvasive technologies, such as functional magnetic resonance imaging (MRI) and positron emission tomography, have revealed brain areas involved in human vocal communication and imaged the metabolic signals reflecting their auditory—vocal association [2]. However, little is known about the neural processing that underlies sensory—motor integration for the learned vocal signals.

Songbirds, a diverse group of avian species classified as the order Passeriformes, provide an attractive model system. These avian species, much like humans, learn to imitate complex vocal signals of their elders during early life and maintain their spectral and temporal structures throughout their whole life [3–6]. Toward the understanding of the brain function to enable learned vocal communication, recent studies investigating the neural basis of songbird vocal behavior have been addressing a key issue: How do individual neurons establish sensory—motor correspondence for learned communication signals?