Synaptic Mechanisms for Auditory-vocal Integration and the Correction of Vocal Errors

A central goal of neuroscience is to understand the cellular mechanisms enabling the cultural transmission of behaviors, such as speech and music. Birdsong is a rare non-human instance of a culturally transmitted vocal behavior. The songbird's brain provides a powerful system in which to study the cellular mechanisms underlying auditory-guided vocal learning. Identifying those mechanisms requires an analysis of synaptic function, because the synapse is the fundamental organizational unit of the neuronal networks that mediate behavior. Intracellular recordings provide a powerful method for simultaneously probing the activities of a single neuron and the synaptic networks in which that cell is embedded. This chapter details initial steps in the in vivo intracellular analysis of the synaptic connectivity of neurons important to singing and song learning. Our analysis is focused upon HVC and involves studies of interneurons as well as projection neurons of the two major output pathways of HVC. We test predictions derived from several models of how such learning may take place, including contributions from "comparator" and "corollary discharge" auditory feedback cancellation mechanisms. Our studies in anesthetized animals and brain slices provide insight into the synaptic properties of HVC that might be well suited for these mechanisms, although extrapolation to synaptic behavior in the awake, singing bird must be made with caution. We suggest that future work must extend the analysis of synaptic properties into the intact brain of the songbird, preferably as the bird learns to sing.