Chapter 3 : Decrystallization of adult birdsong by perturbation of auditory feedback

Young birds learn to sing by using auditory feedback to compare their own vocalizations to a memorized or innate song pattern; if they are deafened as juveniles they will not develop normal songs (Konishi, 1965; Nottebohm, 1968). The completion of song development is called crystallization. After this stage, song shows little variation in its temporal or spectral properties. However, the mechanisms underlying this stability are largely unknown. Here we present evidence that auditory feedback is actively used in adulthood to maintain the stability of song structure. We found that perturbing auditory feedback during singing in adult zebra finches caused a slow deterioration of song. This "decrystallization" consisted of a dramatic loss of the spectral and temporal stereotypy seen in crystallized song, and included stuttering, creation, deletion and distortion of song syllables. After normal feedback was restored, these deviations gradually disappeared and the original song was recovered. Thus, the brains of adult birds that do not learn new songs nonetheless retain a significant amount of plasticity.