Representation of the bird's own song in the canary HVC: contribution of broadly tuned neurons.

In songbirds, neurons in the song nucleus HVC exhibit a striking example of selective auditory response, firing more to playback of the bird's own song (BOS) than to conspecific songs. This song selectivity has been found in various songbird species, both those that sing a single individual-specific song as well as those, such as the canary, in which both song structure and individual-identity encoding in song is more complex. In the present study, we investigated how the BOS is represented in the HVC of anesthetized long-day canaries by using temporal and spectral variants of the BOS stimulus. We addressed the question of how selective HVC neurons were by quantifying the number of song elements, called phrases, that evoked auditory responses. Phrases that were individual-specific or that were frequently delivered in an individual's songs did not drive HVC neurons to a greater degree than others. Reordering phrases or altering their acoustic structure caused a decrease in the auditory responsiveness of HVC neurons. This sensitivity to the spectral and temporal features of the BOS involved neurons that failed to respond to BOS variants or were driven by a reduced number of phrases, as well as neurons whose auditory responsiveness extended beyond the features of the individual's song, responding to phrases that were not sung by the bird itself. Therefore, the neural strategy by which BOS structure is represented in the canary HVC may require something other than a strict representation of the repertoire of song components. We suggest that the individual's song could be coded, at least in part, by an ensemble of broadly tuned neurons.