Conversation is an art, they say. But we’re not the only ones who practice it. Other species do too. The males of the singing mouse of Alston (Scotinomys teguina) from the Cloud Forests of Costa Rica sing melodies with almost a hundred audible notes to attract females. They challenge each other by singing their exclusive, high-pitched songs in turns, alternating like when humans have a dialogue. In contrast, laboratory mice produce ultrasonic squeaks with no obvious changes. Researchers at New York University School of Medicine have discovered that both these singing mice and people have a specific brain circuit that allows them to interact vocally with great skill. The finding, the authors say, may help design new treatments for patients with autism or traumatic events, such as a stroke.
To achieve a successful conversation with another human, for example, we must listen to his words, interpret the meaning, and then respond appropriately with our own statement. It is a process that requires almost instantaneous coordination between sensory signals and muscle response, although little is known about the mechanisms that allow social interactions based on speech or sound exchanges. “Our work directly demonstrates that a region of the brain called the motor cortex is needed” for conversation, says lead author Michael Long.
Cover of “Science” magazine
Cover of “Science” magazine
The study, to which the journal Science has dedicated its cover, found that, along with the brain areas that tell muscles to create notes, separate circuits in the motor cortex allow for quick starts and stops that form a conversation between vocal partners.
“By segregating sound production and control circuits, evolution has equipped the brains of singing mice with strict vocal control that is also seen in cricket exchanges, bird duets and, possibly, human discussion,” adds study co-author Arkarup Banerjee.
Despite the ubiquity of vocal exchanges in the natural world, says the researcher, there are no mammalian models suitable in neuroscience for study. Prior to the new report, the primary model for studying this roundtrip was the marmoset, a primate whose conversational turns are considerably slower than human speech and are unlikely to be due to rapid muscle response to sensory signals (e.g., motor cortical circuits).
Different social songs
The research team discovered that S. teguina’s songs, a series of notes that evolve predictably as the song progresses, changed in social situations to listen to the other and converse, in turn-based behavior much like human behavior. The close connection between song patterns and readings taken by electromyography, which captures electrical signals as the brain generates muscle contractions, allowed the team to determine the relationships between brain centers and the muscle response of the songs, while two mice coordinated their responses. Thus, for the first time, the researchers found that the orofacial motor cortex regulated the synchronization of the song.
The researchers believe their mouse model can guide the related exploration of speech circuits in the human brain. By understanding the activity that helps involve two brains in conversation, they can look for processes that go wrong when the disease interferes with communication, which could stimulate the development of new treatments for many disorders.