ANATOMICAL AND SYNAPTIC SUBSTRATES FOR AVIAN SONG LEARNING

In songbirds, vocal learning occurs during periods of major cellular a nd synaptic change. This neural reorganization includes massive synapt ogenesis associated with the addition of new neurons into the vocal mo tor pathway, as well as pruning of connections between song regions. T hese observations, coupled with behavioral evidence that song developm ent requires NMDA receptor activation in specific song nuclei, suggest that experiences associated with vocal learning are encoded by activi ty driven, Hebbianlike processes of synaptic change akin to those impl icated in many other forms of developmental plasticity and learning. I n this review we discuss the hypothesis that development and/or season al changes in NMDA receptor function and the availability of new synap ses may modulate thresholds for plasticity and thereby define sensitiv e periods for vocal learning. (C) 1997 John Wiley & Sons, Inc.