REASSESSING THE MECHANISMS AND ORIGINS OF VOCAL LEARNING IN BIRDS

The most widely accepted hypothesis of vocal imitation in birds pre-dates many recent studies on the behavior, anatomy, physiology and cell biology of this phenomenon. It states that vocal learning involves two steps: (1) an auditory memory is laid down, and then (2) vocal output is modified until the auditory feedback it generates matches the model 1. This black-box model of vocal imitation disregards circuitry. We now know that the brain pathways for vocal learning in birds include a series of well-defined nuclei and projections 2-5. Some of these nuclei and projections develop late in ontogeny, at the time when auditory models are first acquired and imitated 6-9. We also know that the pathways involved in song production respond to sound, an observation that blurs the demarcation between what is an auditory and what is a motor circuit 10-12. These and other recent discoveries call for a reassessment of the mechanisms and origins of vocal learning in birds and mammals.