Distributed and selective auditory representation of song repertoires in the avian song system

For many songbirds, the vocal repertoire constitutes acoustically distinct songs that are flexibly used in various behavioral contexts. To investigate how these different vocalizations are represented in the song neural system, we presented multiple song stimuli while performing extracellular recording in nucleus HVC in adult male song sparrows Melospiza melodia, a species known for its complex vocal repertoire and territorial use of song. We observed robust auditory responses to natural song stimuli in both awake and anesthetized animals. Auditory responses were selective for multiple songs of the bird's own repertoire (BOR) over acoustically modified versions of these stimuli. Selectivity was evident in both awake and anesthetized HVC, in contrast to auditory selectivity in zebra finch HVC, which is apparent only under anesthesia. Presentation of multiple song stimuli at different recording locations demonstrated that stimulus acoustic features and local neuronal tuning both contribute to auditory responsiveness. HVC auditory responsiveness was broadly distributed and nontopographic. Variance in auditory responsiveness was greater among than within HVC recording locations in both anesthetized and awake birds, in contrast to the global nature of auditory representation within zebra finch HVC. To assess the spatial consistency of auditory representation within HVC, we measured the repeatability with which ensembles of BOR songs were represented across the nucleus. Auditory response ranks to different songs were more consistent across recording locations in awake than in anesthetized animals. This spatial reliability of auditory responsiveness suggests that sound stimulus acoustic features contribute relatively more to auditory responsiveness in awake than in anesthetized animals.