Contributions of the anterior forebrain pathway to vocal plasticity.

The anterior forebrain pathway (AFP) is a basal ganglia-dorsal forebrain circuit that is prominent specifically in birds that learn to sing. This circuit is interconnected with the song motor pathway, is active during song production, and contains neurons that are selective for the sound of the bird's own song, suggesting an important role for the AFP in vocal behavior. However, interruption of the AFP by lesions in adult birds has little overt effect on the production of learned song. In contrast, lesions in juvenile birds prevent the normal progression of song learning. Moreover, lesions in adults, while not disrupting production, can prevent experience-dependent plasticity of song. Such data implicate the AFP specifically in song learning and vocal plasticity. This chapter reviews some of the experimental evidence supporting a role for the AFP in these processes and discusses potential instructive and permissive functions of the AFP in vocal plasticity.