By studying the rapid song-like responses of singing tropical mice, researchers have discovered a neural mechanism that may support the high-speed back and forth vocal exchanges that characterize human conversation. Insights from the new rodent model used in this study open the door for understanding complex speech circuits in human brains, which, when disrupted, lead to life-altering conditions. In order to have a successful conversation with another human, we must listen to their words, interpret the meaning and then respond appropriately with our own statement. While many animals communicate using their voices, very few demonstrate the rapid back-and-forth dynamic exchanges that mimic human conversation. It's a process that requires the near-instant coordination of sensory cues and muscle response, although little is known about the mechanisms that underlie it. The Alston's singing mouse (Scotinomys teguina), a small rodent with a big voice from the cloud forests of Central America, challenges its competitors with dueling duets; each mouse rapidly takes turns singing its unique high-pitched songs to the other. However, according to the authors, each mouse's song changes in response to that of the other, and the participating mice exhibit turn-taking behaviors similar to those of human conversation. Using several neurophysiological techniques, Daniel Okobi and colleagues investigated the underlying neuronal networks that make the counter-singing behavior of S. teguina possible. By tracing the electrical signals between the brain and muscles as two mice sang to one another, Okobi et al. discovered areas within the motor cortex responsible for the muscle control required for generating the notes of each song. Another functional "hotspot" of activity identified within the motor cortex - the vocal motor cortex - was found to mediate the rapid sensorimotor transformations required for rapid and precise vocal interactions. According to the authors, the functional separation and hierarchy of sound generation and timing functions seen in the mice is what makes effective vocal communication possible. In a related Perspective, Steffan Hage discusses the implications of the study's findings on understanding the evolution of vocal communication systems, which likely had their beginnings far earlier than previously thought.
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Journal
Science