Syringeal EMGs and synthetic stimuli reveal a switch-like activation of the songbird's vocal motor program

Response of wild songbirds to songs synthesized with a low-dimensional model

In this work, we used a dynamical system derived from an avian vocal production model to generate synthetic songs that mimic the Zonotrichia capensis songs. We confirmed that these synthetic renditions elicited behavioral responses similar to those evoked by real songs in wild songbirds of the same species. Specifically, we observed an increase in the singing rate of individual birds when a playback device was introduced into their territories. The success of our approach instills confidence in the hypotheses underpinning the model and provides a valuable tool for investigating a wide range of biological questions.

Synthesizing avian dreams

During sleep, sporadically, it is possible to find neural patterns of activity in areas of the avian brain that are activated during the generation of the song. It has recently been found that in the vocal muscles of a sleeping bird, it is possible to detect activity patterns during these silent replays. In this work, we employ a dynamical systems model for song production in suboscine birds in order to translate the vocal muscles activity during sleep into synthetic songs. Besides allowing us to translate muscle activity into behavior, we argue that this approach poses the biomechanics as a unique window into the avian brain, with biophysical models as its probe.

Synthetic Birdsongs as a Tool to Induce, and Iisten to, Replay Activity in Sleeping Birds

Birdsong is a complex vocal behavior, which emerges out of the interaction between a nervous system and a highly nonlinear vocal device, the syrinx. In this work we discuss how low dimensional dynamical systems, interpretable in terms of the biomechanics involved, are capable of synthesizing realistic songs. We review the experimental and conceptual steps that lead to the formulation of low dimensional dynamical systems for the song system and describe the tests that quantify their success. In particular, we show how to evaluate computational models by comparing the responses of highly selective neurons to the bird's own song and to synthetic copies generated mathematically. Beyond testing the hypothesis behind the model's construction, these low dimensional models allow designing precise stimuli in order to explore the sensorimotor integration of acoustic signals.

Replay of innate vocal patterns during night sleep in suboscines

Activation of forebrain circuitry during sleep has been variably characterized as 'pre- or replay' and has been linked to memory consolidation. The evolutionary origins of this mechanism, however, are unknown. Sleep activation of the sensorimotor pathways of learned birdsong is a particularly useful model system because the muscles controlling the vocal organ are activated, revealing syringeal activity patterns for direct comparison with those of daytime vocal activity. Here, we show that suboscine birds, which develop their species-typical songs innately without the elaborate forebrain-thalamic circuitry of the vocal learning taxa, also engage in replay during sleep. In two tyrannid species, the characteristic syringeal activation patterns of the song could also be identified during sleep. Similar to song-learning oscines, the burst structure was more variable during sleep than daytime song production. In kiskadees (Pitangus sulphuratus), a second vocalization, which is part of a multi-modal display, was also replayed during sleep along with one component of the visual display. These data show unambiguously that variable 'replay' of stereotyped vocal motor programmes is not restricted to programmes confined within forebrain circuitry. The proposed effects on vocal motor programme maintenance are, therefore, building on a pre-existing neural mechanism that predates the evolution of learned vocal motor behaviour.

The neurobiology of innate and learned vocalizations in rodents and songbirds

Vocalizations are an important medium for sexual and social signaling in mammals and birds. In most mammals other than humans, vocalizations are specified by innate mechanisms and develop normally in the absence of auditory experience. By contrast, juvenile songbirds memorize and copy the songs of adult tutors, a process with many parallels to human speech learning. Despite the centrality of vocal learning to human speech, vocal production in humans as well as in songbirds exploits ancestral circuitry for innate vocalizations, and effective vocal communication depends on the fluent blending of innate and learned elements. This review covers recent advances in our understanding of central mechanisms for learned and innate vocalizations in birds and mice, including brainstem mechanisms that help to 'gate' vocalizations on or off, cortical involvement in learned and innate vocalizations, and the delineation of circuits that evaluate and reinforce song performance to facilitate vocal learning.