Song-selective auditory circuits in the vocal control system of the zebra finch.

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Birdsong is a learned behavior controlled by a distinct set of brain nuclei. The song nuclei known as area X, the medial nucleus of the dorsolateral thalamus (DLM), and the lateral magnocellular nucleus of the anterior neostriatum (L-MAN) form a pathway that plays an important but unknown role in song learning. One function served by this circuit might be auditory feedback, which is critical to normal song development. We used single unit recordings to demonstrate that all three of these nuclei contain auditory neurons in adult male zebra finches (Taeniopygia guttata). These neurons are song selective: they respond more robustly to the bird's own song than to songs of conspecific individuals, and they are sensitive to the temporal structure of song. Auditory neurons so highly specialized for song within a pathway required for song learning may play a role in the auditory feedback essential in song development. Recordings in the robust nucleus of the archistriatum (RA), the nucleus to which L-MAN projects, showed that RA also contains highly song-selective neurons. RA receives a direct projection from the caudal nucleus of the ventral hyperstriatum (HVc) as well as from L-MAN. We investigated the contributions of these two inputs to auditory responses of RA neurons by selectively inactivating one or both inputs. Our results suggest that there is a song-selective pathway directly from HVc to RA in addition to the circuit via L-MAN. Thus the songbird brain contains multiple auditory pathways specialized for song, and these circuits may vary in their functional importance at different stages of learning.

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