Each animal number is indicated under the bar. Each dot and bar represents individual values and mean ± SEM, respectively, of testosterone concentrations (nanograms per milliliter). No significant difference was observed in serum testosterone between the two groups at any developmental stage. ![]() B, Average levels of circulating testosterone at three developmental stages, juvenile (dph 50–60), young (dph 105–130), and old (older than dph 330), in the intact (blue bars) and early-deafened (orange bars) birds. Sixteen early-deafened birds from four families are indicated. A, Zebra finches deafened at dph 18–22 developed unique song patterns with a characteristic motif-like structure (colored shadings) at the old adult stage (older than dph 300). Individual differences in stabilized song patterns in early-deafened zebra finches. Mean ± SEM (intact, n = 4 socially isolated, n = 5 early-deafened, n = 6 Student's t test with Bonferroni's correction, ** p < 0.01). A value near 0 indicates a crystallized/stabilized song pattern. The values of K–L distance at dph 45–59 are normalized as 1.0. D, Normalized K–L distance calculated from the last syllable scatter plot representing crystallized/stabilized song patterns. Orange shading highlights stable song motifs. C, Examples of song development and syllable scatter plots (duration vs mean FM) in two early-deafened zebra finches. The crystallized song pattern of the socially isolated bird is similar to that of the intact bird, except for a prolonged and variable syllable (green bracket). The intact and socially isolated birds exhibited song stability at approximately dph 110. Color shadings (blue and green) highlight stable song motifs. A, B, Examples of song development and syllable scatter plots (duration vs mean FM) in an intact ( A) and a socially isolated ( B) bird. These results indicate a genetic program-associated inevitable termination of vocal plasticity that results in audition-independent vocal crystallization.Ĭritical period deaf motor pattern generation sensorimotor learning songbird species specificity.Ĭopyright © 2015 the authors 0270-6478-12$15.00/0.Ĭomparison of song development and stabilization in intact, socially isolated, and early-deafened zebra finches. Furthermore, even after adult deafening, which degrades crystallized song, the deteriorated songs ultimately restabilized at the same point when the early-deafened birds stabilized their songs. ![]() In contrast to the different rates of song development between the intact and deafened birds, developmental gene expression in the motor circuit is conserved in an age-dependent manner from the juvenile stage until the older adult stage, even in the deafened birds, which indicates the audition-independent robustness of gene expression dynamics during development. Compared with intact zebra finches, early-deafened zebra finches showed excessively delayed vocal development, but their songs eventually crystallized. Using audition-deprived songbirds, we examined whether auditory experience affects developmental gene expression in the major elements of neural circuits that mediate vocal learning and production. Although auditory input is crucial for acquiring complex vocal patterns, its exact role in neural circuit maturation for vocal learning and production is not well understood. Song is primarily learned during a specific developmental stage called the critical period. Birdsong, like human speech, is a complex vocal behavior acquired through sensorimotor learning and is based on coordinated auditory input and vocal output to mimic tutor song. Complex learned behavior is influenced throughout development by both genetic and environmental factors.
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