In a study published May 31 in Proceedings of the National Academy of Sciences, a team of researchers studying the brain activity of singing male and female plain-tailed wrens has discovered that the species synchronize their frenetically paced duets, surprisingly, by inhibiting the song-making regions of their partner's brain as they exchange phrases.
Researchers say that the auditory feedback exchanged between wrens during their opera-like duets momentarily inhibits motor circuits used for singing in the listening partner, which helps link the pair's brains and coordinate turn-taking for a seemingly telepathic performance. The study also offers fresh insight into how humans and other cooperative animals use sensory cues to act in concert with one another.
Eric Fortune, co-author of the study and neurobiologist at New Jersey Institute of Technology's Department of Biological Sciences said, you could say that timing is everything, what these wrens have shown us is that for any good collaboration partners need to become one through sensory linkages. The take-home message is that when we are cooperating well. We become a single entity with our partners.
Melissa Coleman, the paper's corresponding author and associate professor of biology at Scripps College said, think of these birds like jazz singers. Duetting wrens have a rough song structure planned before they sing, but as the song evolves, they must rapidly coordinate by receiving constant input from their counterpart. What we expected to find was a highly active set of specialized neurons that coordinate this turn-taking, but instead what we found is that hearing each other actually causes inhibition of those neurons, that's the key to regulating the incredible timing between the two.
For the study, the team had to travel to the heart of the plain-tail wren music scene, within remote bamboo forests on the slopes of Ecuador's active Antisana Volcano. Camped at the Yanayacu Biological Station's lab, the team made neurophysiological recordings of four pairs of native wrens as they sang solo and duet songs, analyzing sensorimotor activity in a premotor area of the birds' brains where specialized neurons for learning and making music are active.
The recordings showed that during duet turn-taking which often takes the form of tightly knit call-and-answer phrases, or syllables, together with sound as if a single bird is singing, the bird's neurons fired rapidly when they produced their own syllables. Yet, as one wren begins to hear their partner's syllables sung in the duet, the neurons quiet down significantly.
Fortune said, you can think of inhibition as acting as a trampoline. When the birds hear their partner, the neurons are inhibited, but just like rebounding off a trampoline, the release from that inhibition causes them to swiftly respond when it's their time to sing.
Next, the team played recordings of wrens duetting while they were in a sleep-like state, anesthetized with a drug that affects a major inhibitory neurotransmitter in the wrens' brains that is also found in humans, gamma-aminobutyric acid (GABA). The drug transformed the activity in the brain, from inhibition to bursts of activity when the wrens heard their own music.
Fortune said, these mechanisms are shared or similar to what happens in our brains because we are doing the same kind of things. There are similar brain circuits in humans that are involved in learning and coordinating vocalizations.
Fortune and Coleman say the results offer a fresh look into how the brains of humans and other cooperating animals use sensory cues to act in concert with each other, from flowing musical and dance performances, or even the disjointed feeling of inhibition commonly experienced today during video conferencing.
Coleman said, these days, inhibition is occurring at all the wrong times when we have poor internet connections during our Zoom, WebEx, and Facetime conferences. The delays affect the sensory information that we rely on for coordinating the timing of our conversations. I think this study is important for understanding how we interact with the world whenever we are trying to produce a single behavior as two performers. We are wired for cooperation, the same way as these jazz singing wrens.