Early onset of deafening-induced song deterioration and differential requirements of the pallial-basal ganglia vocal pathway.

Similar to humans, songbirds rely on auditory feedback to maintain the acoustic and sequence structure of adult learned vocalizations. When songbirds are deafened, the learned features of song, such as syllable structure and sequencing, eventually deteriorate. However, the time-course and initial phases of song deterioration have not been well studied, particularly in the most commonly studied songbird, the zebra finch. Here, we observed previously uncharacterized subtle but significant changes to learned song within a few days following deafening. Syllable structure became detectably noisier and silent intervals between song motifs increased. Although song motif sequences remained stable at 2 weeks, as previously reported, pronounced changes occurred in longer stretches of song bout sequences. These included deletions of syllables between song motifs, changes in the frequency at which specific chunks of song were produced and stuttering for birds that had some repetitions of syllables before deafening. Changes in syllable structure and song bout sequence occurred at different rates, indicating different mechanisms for their deterioration. The changes in syllable structure required an intact lateral part but not the medial part of the pallial-basal ganglia vocal pathway, whereas changes in the song bout sequence did not require lateral or medial portions of the pathway. These findings indicate that deafening-induced song changes in zebra finches can be detected rapidly after deafening, that acoustic and sequence changes can occur independently, and that, within this time period, the pallial-basal ganglia vocal pathway controls the acoustic structure changes but not the song bout sequence changes.