Have you ever stopped to wonder about how quickly our brains must work in order to participate in a conversation?
In order to do this, we and our brains must be capable of high-speed processing, an intricate set of calculations that allow us to process what another person has said and then formulate a response, all within microseconds.
How this works exactly, like so much of what happens in our brains, has been a mystery to scientists for generations.
Recently, however, a new study of mice in the cloud forests of Costa Rica has offered some insight into how this process may work. Scientists studying mice have discovered a brain circuit that may be part of the reason that we can engage in this high-speed set of calculations.
Yes. Singing mice.
Researchers at the NYU School of Medicine and UT Austin recently undertook a study of the Alston’s singing mouse, a small rodent living in the forests of Costa Rica. The study was led by scientists from the NYU Neuroscience Institute and Department of Otolaryngology in collaboration with the Center for Brain, Behavior, and Evolution at the University of Texas at Austin.
The mouse, known as Scotinomys teguina, lives in the cloud forests of Costa Rica. Cloud forests, also sometimes known as fog forests, are tropical or subtropical moist forests that have frequent or seasonal low-level cloud cover, usually at the canopy level. This makes the trees of the forest look as if they are swimming in clouds.
The Alston’s singing mouse lives in these forests from Panama to southern Mexico and is abundant in the cloud forests of Costa Rica.
These mice have what’s been termed an “uncanny repertoire” of vocalizations that range from high-speed chirps to clicking. Many of these songs are inaudible to humans, falling into ultrasonic frequencies. Both males and females sing, often as part of mating rituals.
What Have We Learned by Studying These Mice?
The males of Scotinomys teguina communicate both with females and with other males, taking turns, as if in a conversation. This is why the songs are interesting to scientists studying the way that brains work in conversations.
This is called “vocal turn-taking,” and it is a function that needs sub-second precision, or precision of less than a second.
Researchers at New York University found, in studying the singing mice, that a brain region in these mice called the motor cortex gets used very similarly to the way that a human’s motor cortex gets used during conversations. This helps confirm that the motor cortex is the most necessary part of the brain for the ability to hold a conversation.
Scientists found in both human and mouse brains that different circuits within the motor cortex send signals to our vocal muscles that tell those muscles when to create notes or sounds, while a separate circuit in the same part of the brain controls the fast starts and stops that make a conversation possible.
Specifically, researchers found a functional “hotspot” in mouse brains that was located at the front of the motor cortex on one side. This spot, the orofacial motor cortex (or OMC), was shown to regulate the timing of the mice’s songs. According to the scientists, they observed this specific part of the brain functioning separately during periods of sound generation and timing.
This is new and exciting information about how mammalian motor cortical circuity works. In previous studies, scientists relied on marmosets, who also have conversational interactions, but at a much slower rate than humans. This mouse research replicates the rapidity of the way the circuits fire.
Why Do We Care?
Besides being cool, what applications might this research have going forward?
Scientists involved in the project are already using the model designed by studying mouse brains to guide their exploration and research into human speech circuits. This allows them to look specifically for faults or glitches in the human brain that impair communication in the case of disease, disorders or injuries such as autism, strokes, concussions or skull fractures.
By being able to identify what exactly is misfiring in these brain circuits to impede communication and conversation, researchers hope to be able to develop new treatments for many disorders and restore the ability to have conversations to thousands of patients every year.