Auditory experience and adult song plasticity.

Adults Bengalese finches normally sing stereotyped songs, which do not change under the influence of auditory experience. If deafened, however, adult birds sing significantly degraded songs that are characterized by a lack of stereotypy of syllable order and the deterioration of syllable structure. We studied the importance of auditory feedback for maintenance of normal adult song. Auditory feedback can be partially or completely removed by eliminating auditory hair cells, the sensory receptor cells for hearing. The effects are reversible because birds regenerate new hair cells when original cells are lost. Limiting the frequency range of auditory feedback available to birds using partial hair cell lesions indicated that low-frequency information (1500 Hz) is necessary and sufficient for the maintenance of normal adult song. Reversible deafening experiments using hair cell loss and regeneration indicated that adult Bengalese finches store memories of their own songs, which can be used to guide vocal behavior. Additionally, destabilizing song behavior by removing auditory feedback leads to renewed song plasticity, and some adults can be induced to learn new song. These studies suggest that Bengalese finches maintain normal song by comparing ongoing vocal output to stored models of their own stable songs and that neural circuitry for song learning persists beyond the sensitive period for song learning.