Vocal learning in songbirds is a unique, experimentally accessible model of human vocal learning that exemplifies the general process of motor learning. A male songbird learns his song by first memorizing his father's song, and later using auditory feedback to match his own song to the memory of his father's song. When a good match is achieved, the song becomes highly stereotyped and less dependent on auditory feedback. Forebrain nucleus RA is implicated as a site of plasticity for song learning because: (i) it receives convergent motor input from nucleus HVc and auditory input from nucleus L-MAN; (ii) the HVcRA connection is first formed at the onset of song practicing; (iii) and input for L-MAN, which is that nucleus' sole output to the motor system, is crucial for learning, but not for adult song production. Numerous collaterals within RA also contribute the majority of excitatory connections to RA neurons. My working hypothesis is that vocalization driven auditory activity in L-MAN guides selection of motor connections in RA through synaptic enhancement or depression and that this plasticity disappears or becomes substantially reduced after song crystallization. This proposal will (1) measure developmental changes in basic properties of synaptic connections in the L-MAN RA, HVc RA and RA RA pathways using whole cell patch clamp recording in brain slices; (2) determine activity patterns in the three pathways that elicit changes in synaptic strength; and (3) compare plasticity in slices prepared from juveniles and from adults. These studies will be the first to examine a role for changes in synaptic strength in learning of a complex vocal behavior. Progress in illuminating mechanisms underlying plasticity in this system will further our long-term goal of understanding more general mechanisms of learning in the central nervous system.
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