Auditory feedback and song behavior in adult Bengalese finches

Abstract

Thesis (Ph. D.)--University of Washington, 1999 Song learning and maintenance in birds provides a useful model system for studying how experience contributes to the development and control of a socially meaningful motor behavior. Adult male Bengalese finches learn to sing only as juveniles and normally maintain stereotyped and stable song as adults. If adult males are deafened by surgical cochlea removal, song behavior degrades. The sequences of syllables composing songs become variable and the spectral composition of syllables changes. Thus, Bengalese finches require auditory feedback to maintain stable song behavior as adults.The kinds of auditory feedback necessary for song maintenance appear to be either low frequency spectral cues or temporal cues from the song amplitude envelope. If hearing losses spanning the entire Bengalese finch hearing frequency range are caused by auditory hair cell loss, song degradation in birds formerly singing stable song results. If some auditory hair cells are preserved in the apical (low frequency) region of the basilar papilla, hearing thresholds for lower (<2 kHz) frequency sounds are virtually normal. Under these conditions, birds maintain stable song patterns.If birds are allowed to recover from hair cell loss, hair cells regenerate and repopulate the basilar papilla across its entire length, and hearing thresholds are restored to normal levels at lower frequencies. Some high frequency hearing loss persists long-term (up to 8 weeks recovery). During hair cell regeneration, degraded song recovers toward the composition of the original song. Syllable sequences and the spectral composition of syllables are more like the original song after 4 to 8 weeks of recovery than in the first 3 weeks following hair cell loss. These results indicate that a representation of learned song that is independent of ongoing motor behavior is permanently stored in the brain of an adult Bengalese finch. However, consistent alterations in song format (syllable sequence) are present in the songs of birds with regenerated hair cells. Additionally, it is possible that the composition of recovered song can be influenced by the songs of other birds.