Researchers from New York University's School of Medicine have investigated a neotropical and extremely audible rodent called Alston’s singing mouse, finding that the mouse’s relatively unique vocalizations could prove an excellent model for studying human conversation.
By examining the brains of these musical mice, the authors discovered neural circuits that guided the quick back-and-forth interaction that is a distinctive feature of their songs. The findings open up valuable research avenues for studying the brain processes that underlie speech disabilities and communication impairments in humans. The paper is published in Science.
Singing to a different tune
Vocal calling and exchanges are everywhere in nature, from birdsong to the whistling of bottlenose dolphins, but animal models that mimic human conversation have been lacking. In humans, the brain must process the information encoded in another’s speech and provide an appropriate response almost instantly. Turn-taking vocalization styles have previously been noted in marmoset monkeys, but marmosets have slower interactions that take far longer than the rapid replies seen in humans. Alston’s singing mice, on the other hand, are capable of quick and complex conversation. Male singing mice become vocal both to allure females and challenge rivals. This behavior is distinct from other mice, as study lead author Michael Long, an associate professor of neuroscience at New York University's School of Medicine, explains, “The primary differences between the vocal behavior of Alston’s singing mice and laboratory mice is that the latter produces short, disorganized, ultrasonic vocalizations, while the former make relatively long (~10 s) advertisement calls that consist of nearly 100 notes and follow a predictable structure capable of signaling the identity of the caller.”
The motor behind mouse song
The researchers examined their singing mice using electromyography, a technique which detects the electrical signals produced when the brain generates muscle contractions, such as those required for singing. “We found that the task of interacting vocally is divided into two distinct components: vocal production and vocal coordination, says Long. “We found that a region of the brain – the orofacial motor cortex (or OMC) - is necessary for vocal coordination, while song production (or the creation of individual notes) is carried out elsewhere. This is the first demonstration of the neural mechanisms that lead to vocal coordination in the mammalian brain.”
Male Alston's singing mouse singing to female in estrus. Credit: country mouse studios via YouTube
It is this separation between the making of songs and their timing that make quick vocal communication possible, as study co-first author, Dr Arkarup Banerjee, explains, "By segregating sound production and control circuits, evolution has equipped the brains of singing mice with the tight vocal control also seen in cricket exchanges, bird duets, and possibly, human discussion."
The team investigated the brain mechanisms behind the songs, using devices that “cooled” the OMC during the mice’s songs. This cooling safely reduced the speed of the song, without changing the tone or pitch of the notes, showing the functional separation of the OMC from note-making brain areas.
Can songs fix communication gone wrong?
The authors are using the singing mouse to guide similar research into human speech that could eventually help to treat patients with communication disorders. Long points out that these disorders effect one in ten people, with causes including autism and brain injury. “We lack basic understanding of the brain mechanisms that enable conversations,” says Long. “Studying vocal communication in Alston’s singing mouse - a mammalian species that engage in fast conversations like us - provides a platform for discovering common brain mechanisms that might inform potential cures in the future.”