Species Differences in Auditory Processing Dynamics in Songbird Auditory Telencephalon

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The caudomedial nidopallium (NCM) of songbirds is a telencephalic area involved in the auditory processing and memorization of complex vocal communication signals. We used pure tone stimuli and multiunit electrophysiological recordings in awake birds to investigate whether the basic properties of song-responding circuits in NCM differ between canaries and zebra finches, two species whose songs are markedly different in their spectral and temporal organization. We found that the responses in zebra finch NCM are characterized by broad tuning and sustained responses that may facilitate the integration of zebra finch song syllables and call notes that are of long duration and have a broad harmonic structure. In contrast, we found that the responses in canary NCM show narrower tuning and less sustained responses over the time periods analyzed. These characteristics may contribute to enhanced processing of the narrow-band whistles, rapid trills, and steep frequency modulations that are prominent features of canary song. These species differences are much less pronounced in field L2, the direct thalamorecipient region that represents a preceding station in the central avian auditory pathway. NCM responses did not differ across sexes of either species, but field L2 did show wider tuning in zebra finch females relative to males. In sum, species differences in the response properties of NCM likely reflect selectivity for the acoustic elements of each species' vocal repertoire.