The long term goal of our laboratory is to understand how the brain changes with sensory learning, and what factors constrain learning-dependent changes. Vocal learning in birds provides a useful model to address these questions, because it is clear that songbirds must hear and memorize song early in life in order to sing normally as adults. Furthermore, birds have specialized brain structures devoted to song learning, in which many of the important neural changes are likely to occur. Young birds, like humans, show behavioral evidence of innate responsiveness to their own species' vocalizations. They must subsequently be exposed to adult song within a critical period if they are to memorize this song correctly. The general goal of the experiments proposed here is therefore 1) to investigate patterns of neural activity in the song system of birds prior to learning, to look for neural mechanisms which might mediate the innate behavioral responses to song, and then 2) to assess how this initial state of the nervous system is affected by subsequent sensory exposure or the lack thereof. We hypothesize that the innate capacity of songbirds to recognize songs of their own species (conspecific song) is encoded by auditory neural circuitry in and afferent to the song system. We propose to examine these areas systematically in juvenile birds, prior to song exposure, for the presence of neurons or ensembles of neurons that respond to stimuli known to elicit selective responses in behavioral studies. Such neurons might represent the innate template thought to underly conspecific song recognition. We will then examine the same areas after birds have had a period of sensory experience of song or of song deprivation. These experiments will provide insight into the effects of exposure to complex acoustic stimuli and how these stimuli might be represented in the spatiotemporal patterns of neural activity. We will compare our results in detail with our Program Project colleagues, especially Schreiner, who is analyzing mammalian auditory cortex before and after learning of complex sounds. Common principles underlying the effects of sensory experience may emerge from such thematically related studies of different systems. Because the innate responsiveness of songbirds is reminiscent of the innate human responsiveness to phonemes, which narrows with exposure to a specific language, these studies should also shed light on general mechanisms of vocal learning, the neural basis of constraints on vocal learning, and mechanisms of critical period closure.
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