Vocal turn-taking in zebra finches is regulated by inhibition with the premotor nucleus HVC.
a) Calls (indicated by blue lines) in response to 1-Hz call playback (in grey) b) Schematic of the vocal motor pathway in the zebra finch brain. c) Call response timing when the impact of inhibition within HVC is reduced (via application of the GABA(A) - antagonist gabazine. d) Example intracellular recordings of HVC premotor neurons and interneurons during call production.
About
What are the developmental changes that occur in the songbird brain during the process of song learning?
Previously, we discovered a synaptic mechanism that is critical for shaping observational learning for singing behavior (Vallentin, Kosche et al. 2016). While the birds were engaged in the learning process, we focused on the activity within a forebrain cortical region called HVC that is centrally important for song production.
HVC contains premotor neurons that ultimately influence song-related musculature as well as a range of local circuit inhibitory interneurons. We recorded from premotor neurons in juvenile zebra finches while the birds were listening to their tutor’s song while carefully tracking the learning trajectory of those birds over several weeks. In inexperienced birds, we found that simply hearing the father’s song activates the same premotor neurons that the zebra finch will eventually use to produce his own song. Once the song had been mastered, however, premotor neurons stopped responding to the tutor song. In further experiments, we found that the responses to the tutor song were being actively suppressed by synaptic inhibition.
To learn more about this inhibitory suppression, we directly measured the activity of inhibitory interneurons within HVC. The suppression of the tutor song through HVC inhibition was more strongly correlated with learning rather than developmental age. As the bird acquires his song and establishes his ideal motor program, this circuit became increasingly protected from any outside influences. This new insight not only completely redefines the role of inhibition in developing neural circuits, but also leads to the question about the origin of the auditory evoked inputs.
Research Questions
Where and how does the neural memory of the song template emerge?
We are combining targeted song training and behavioral observations with electrophysiological recordings in awake behaving zebra finches in order to investigate how the neural memory of the song template emerges in higher-order auditory areas and how it is consolidated in the motor program during song learning.
How do songbirds coordinate their vocalization with each other?
Songbirds can take turns when exchanging songs or calls with one another, much like humans do during conversations. We found that birds time their vocalizations in response to a vocal partner (Benichov et al. 2016, 2020) and that the premotor nucleus HVC is necessary for this type of precise coordination. Inhibition within this nucleus is primarily involved in the regulation of vocal timing i.e. when to vocalize and when to withhold a vocalization to avoid overlapping with another bird. Further playback experiments with different songbirds in the lab and in the field allow us to explore the vocal turn-taking capabilities in detail. The main question that we aim to answer is how auditory signals guide vocal motor outputs on a millisecond timescale.