Auditory-vocal-cholinergic pathway in avian song learning

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1. Male zebra finches learn to imitate a tutor's song through auditory and motor learning. The two main song control nuclei in the bird brain, the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), receive cholinergic innervation from the ventral paleostriatum (VP) of the basal forebrain which may play a key role in song learning. By injecting neuroanatomical tracers, we found a topographically segregated pathway from nucleus ovoidahs (Ov) to VP that in turn projects in a topographic fashion to HVC and RA.Ov is a major relay in the main ascending auditory pathway. The results suggest that the cholinergic neurons in the VP responsible for song learning are regulated by auditory information from the Ov.2. Auditory-motor interaction is essential for the understanding of avian song learning and maintenance. The HVC nucleus is thought to be the most important station for auditory-motor integration in the avian song system. However, little is known about where and how auditory inputs are conveyed into the HVC.The shelf, a multi-auditory recipient region along the ventral border of the HVC, is thought to be a possible source of auditory inputs to the HVC.Here, we investigated the functional connections between the HVC and surrounding area of the HVC including the shelf in the brain slices, using the real-time optical recording technique. Unexpectedly the electrical stimulation of the shelf region did not induce a signal propagation into the HVC, but stimulation within the HVC propagated strong signals into the shelf. These results suggest that the shelf is the region that receives the output signals from the HVC, rather than a major source of auditory inputs to the HVC.