Vocal motor changes beyond the sensitive period for song plasticity

Abstract

Behavior is critically shaped during sensitive periods in development. Birdsong is a learned vocal behavior that undergoes dramatic plasticity during a sensitive period of sensorimotor learning. During this period, juvenile songbirds engage in vocal practice to shape their vocalizations into relatively stereotyped songs. By the time songbirds reach adulthood, their songs are relatively stable and thought to be "crystallized." Recent studies, however, highlight the potential for adult song plasticity and suggest that adult song could naturally change over time. As such, we investigated the degree to which temporal and spectral features of song changed over time in adult Bengalese finches. We observed that the sequencing and timing of song syllables became more stereotyped over time. Increases in the stereotypy of syllable sequencing were due to the pruning of infrequently produced transitions and, to a lesser extent, increases in the prevalence of frequently produced transitions. Changes in song tempo were driven by decreases in the duration and variability of intersyllable gaps. In contrast to significant changes to temporal song features, we found little evidence that the spectral structure of adult song syllables changed over time. These data highlight differences in the degree to which temporal and spectral features of adult song change over time and support evidence for distinct mechanisms underlying the control of syllable sequencing, timing, and structure. Furthermore, the observed changes to temporal song features are consistent with a Hebbian framework of behavioral plasticity and support the notion that adult song should be considered a form of vocal practice.

Maturation‐dependent control of vocal temporal plasticity in a songbird

“…This result is consistent with our data showing a significant difference in the variability of gap duration but not syllable duration between early and late adults, despite the different developmental time scales of two species. Similarly, a study on Bengalese finches has reported that younger birds (6 monthold, corresponded to young and early adult birds in our study) showed significantly greater variability in gap durations but not in syllable durations than older birds (23 month-old, corresponds to our late adult birds) (James and Sakata, 2014), consistent with the present study.…”

“…Additionally, we observed a tendency that target gap durations were shortened with age in NA experiments while non-target gap durations were not. Shrinkage of gap durations during development have been generally observed in previous studies (Glaze and Troyer, 2013;James and Sakata, 2014), then, it would be unclear whether the shrinkage of target gap observed here could be attributed to side effects of NA experiments.…”

“…Thus, the song restarts observed in young birds could be active avoidance of noise hits. It is known that Bengalese finches can slightly change their transition patterns even after mature (James and Sakata, ), and can modify transition probabilities in response to noise feedback in such NA experiments as adults (Warren et al, ). The increase of song restarting rates in young birds observed in the present study could be due to an enhanced version of such sequential plasticity.…”

“…The developmental decrease in the variability of gap durations was replicated in the baseline data of NA experiments. Previous studies have shown that variability in various song features gradually decreases throughout development, both in terms of spectral features, such as fundamental frequency and spectral entropy (Tchernichovski et al, 2004;Kelly and Sober, 2014), and in temporal properties (Glaze and Troyer, 2013;James and Sakata, 2014).…”

Behavioural responses to video and live presentations of females reveal a dissociation between performance and motivational aspects of birdsong

“…To analyse variation in song tempo between VD and LD song, we calculated the duration of the first motif of each song bout and analysed experimental variation in first motif durations using the same four-way factorial model as above (only first three bouts). Only the first motif in each bout was analysed for this comparison because motif durations change as bout length increases (e.g., Chi and Margoliash, 2001; Glaze and Troyer, 2006; James and Sakata, 2014; James and Sakata, 2015) and because bout lengths differed between VD and LD song (Figure 3; Table S2). There was no significant effect of any factor, including Condition, on song tempo (Figure 4C).…”