Neuronal birth and death, and the balance between the two, are fundamental processes of adult neural plasticity. Songbirds are an excellent model for exploring the dynamics of neuronal birth and death, and their effects on behavior, as seasonal production of song is under the control of a discrete but plastic neural circuit. This circuit includes the avian song control nucleus HVC and its target, the robust nucleus of the arcopallium. Seasonal plasticity of HVC in Gambel’s white-crowned sparrows involves pronounced changes in neuron number. Within 7 days of transitioning into breeding conditions, 68,000 new neurons integrate into HVC. Likewise, as birds transition into non breeding conditions, an equal number of neurons (both young and old neurons) die via caspase dependent cell death within 3 days. We exploit these dramatic changes in neuron number between seasons to ask questions about the proximate mechanisms that guide reactive neurogenesis (i.e., the birth of new neurons as a response to HVC cell death), homeostatic neural stem cell proliferation, and mature neuronal survival. We often perform in vivo manipulations with microsurgeries and correlate changes in cell behavior with altered singing behavior.

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