Functional characterization of auditory forebrain in the songbird

Abstract

Songbirds communicate with individualized vocalizations that must be discriminated and recognized based on the detection of complex sound features. Neurons in the primary auditory nucleus of the zebra finch, field L, specialize in extracting auditory features that include rapid fluctuations in temporal envelope, harmonic structure, and dynamic pitch changes. Weused electrophysiological recording and immunohistochemistry to determine the inhibitory network roles and putative connectivity of field L neurons that represent specific kinds of acoustic features. Neuronal responses to conspecific song broadcasts were recorded juxtacellularly from an in vivo anesthetized preparation. At the end of recordings sufficient to calculate a spectrotemporal receptive field (STRF), the cell was filled with Neurobiotin from the patch electrode. Some projections could be traced. A slight majority of recovered auditory neurons were GABA-ergic based on double fluorescent labeling of the Neurobiotin and an antibody for glutamic acid decarboxylase (GAD). The STRFs of the recovered neurons showed a diverse sampling of complex and simpler types of auditory selectivity. This variety should be useful in distinguishing signature features of particular individuals' songs. We hypothesize that uneven distribution of tuning across morphological types and anatomical locations superficial within field L contributes to parallel pathways dedicated to processing distinct categories of acoustic features.