If there was an opera for rodents, the singing mouse of Alston would be the star. This unassuming brown mouse hailing from the cloud forests of Central America stands on its hind legs and belt making it possible to obtain long intricate trills. The performance of each animal seems unique, said Michael Long, neuroscientist at the Faculty of Medicine at New York University in New York. "I can recognize that particular song and say," Oh, it's Ralph. "
Long and his colleagues have now found that the species (Scotinomys teguina) does something that many laboratory animals do not do: sing in turn. And these rapid-fire duets offer researchers a new model for studying how the brain controls the conversation. Mice could even help us understand what is wrong with communication disorders, such as autism.
A human conversation has a lot of moving parts. As we listen, we plan our words, adjust them on the fly and ask our vocal muscles to spit them out at socially appropriate times. Most laboratory animals do not have this verbal complexity, says Long. The most common laboratory mouse (Mus musculus) has a relatively disorganized and unpredictable song, and she does not tend to sing in turn. Even marmosets, primates with back-and-forth calls that make them popular in neuroscience research, pause for several seconds between responses, which means that they can not rely on the same neural mechanism that governs responses in a fraction of a second, according to Long. said. "Imagine a conversation between two people where there is a five-second pause between each exchange. I think I would go crazy.
That's why he and other researchers are interested in Alston's singing mouse. The social functions of his distinctive songs are not yet entirely clear. (The performance seems to be part of a territorial display, though it's not always contradictory.) The species, relatively newcomer to the field of neuroscience, is a bit of a diva in the lab , requiring a spacious terrarium, a specialized diet and exercise equipment to thrive. But Long and his team have discovered an intriguing trend to take their turn in mice. When a male mouse enters a room adjacent to another male and can hear his neighbor singing, she specifically times his own songs to avoid any overlap with the neighbor; it starts about half a second after the end of the other mouse. (In human conversation, the lag is even shorter – about 200 milliseconds on average.) The mouse with a neighbor also sings four times more than when she is alone, the researchers found.
The researchers wanted to know how the mouse brain controlled these carefully programmed exchanges. Numerous studies have shown that animal vocalizations originate from deep and old parts of the brain called subcortical structures. But they wondered if, in this singing mouse, a separate structure in a higher region called the motor cortex acted as an orchestra leader, activating and deactivating the songs according to social cues.
They found various evidence to support this intuition. They first identified a part of the brain called the orofacial motor cortex (OCM) that, when stimulated, bent the vocal muscles of the mouse. When they placed a cooling device on this region to slow down its neuronal activity, the mouse took longer to reach the end of its singing.
In addition, mice could still sing when scientists had given them a drug that had completely disabled MOC – vocalisations were obviously produced elsewhere in the brain – but hearing the song of another mouse was no longer increasing theirs. And the mice have not launched a quick response, researchers said today online in Science. They conclude that, to perform a vocal turn, the mouse brain divides the work between a basic vocal generator (which remains to be identified in the subcortical brain) and a higher-level conductor.
"I think it's beautiful, the combination of methods they applied," says Julia Fischer, an ethologist who studies social behavior and animal cognition at the University of Göttingen in Germany. "This is a major breakthrough in terms of details … they have managed to solve the problem."
Alston's singing mouse is "a potentially interesting new model for voice communication," says Karel Svoboda, a neuroscientist at the Janelia Research Campus at the Howard Hughes Medical Institute in Ashburn, Virginia. However, he added, "We need to know more." This study failed to determine how the MOC affects lower brain activity, he notes, nor how the circuits that move the brain muscles to produce songs.
Human speech is much more complex than these mouse duets, but Long's team now wants to turn to the human brain to find a similar synchronization mechanism in the human motor cortex, known to be involved in speech control. . He and his colleagues are designing experiments that record brain activity during conversation tasks, such as fast response to another voice.
Long also sees this mouse as a potential way to study autism, a disorder that can limit a person's ability to communicate. Researchers could manipulate MOC genes from mice involved in autism to observe their impact on brain activity and behavior. According to Long, turn-based divas have really "opened a new slice of biology for us".