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When monkeys work together, their brains synchronize

One of the greatest mysteries involving the physiology of our brains is the purpose and function of the mirror neurons in our body’s command center. Some neuroscientists believe these neurons are integral to how we relate to each other in our behavior. It’s also possible that deficiencies in mirror neurons play a role in autism and other disorders that are detrimental to social skills.

Past studies have found that when one animal observes another performing a motor task, such as reaching for food, the mirror neurons in the motor cortex of the observing animal’s brain begin to fire as if the observer was also reaching for food. Now, new research from Duke University suggests that mirroring in monkeys may be influenced by social factors, like social hierarchy, proximity to other animals, and competition for food.

For the study, published in the journal Scientific Reports, the researchers discovered that when a pair of monkeys interacts during a social task, both monkey’s brains exhibited episodes of high synchronization. During these episodes, pools of neurons in each monkey’s motor cortex fired at the same time in a phenomenon known as interbrain cortical synchronization (ICS).

“We believe our study has the potential to open a complete new field of investigation in modern neuroscience by demonstrating that even the simplest functions of the motor cortex, such as creating body movements, are heavily influenced by the type of social relationships among the animals participating,” explains senior author Miguel Nicolelis.

What makes this study unique is that the researchers created a multi-channel wireless system to record the electrical activity coming from hundreds of neurons in the motor cortices of two monkeys simultaneously, while the animals interacted in the same space. Previous studies had only recorded brain activity for one animal at a time.

For one of the tasks, one monkey (the passenger) sat in an electronic wheelchair programmed to reach a reward across the room. The second monkey (the observer) was in the same room watching the passenger move towards the reward. The researchers recorded electrical activity in the motor cortex of each subject’s brain simultaneously. Analysis showed that when the passenger traveled across the room while the observer watched, pools of neurons in their motor cortices exhibited episodes of synchronization.

Furthermore, the research team discovered that these episodes of ICS could not only predict the location of the passenger’s wheelchair across the room, they could also predict its velocity. Brain activity could also predict how close the animals were to each other, along with the passenger’s distance from the reward.

To the researchers, the study’s most interesting finding was that ICS could predict the rank of the monkeys in the colony. For tasks when the colony’s most dominant monkey was the passenger and the lower-ranking monkey was the observer, the magnitude of ICS grew steadily as the passenger got closer to the observer. But when the lower-ranking monkey was the passenger and the dominant monkey was the observer, ICS did not increase as the monkeys got closer. This suggests that social rank may play a role in brain synchronization.

The study’s authors believe that episodes of ICS were initiated by the simultaneous activation of mirror-neurons in both monkey’s brains. They believe that similar connections between brain synchrony and social interaction may take place during social interactions between humans as well. Further research could pave the way for new treatments or diagnostics for conditions that involve deficiencies in neuronal mirroring, like autism. Measuring ICS in humans could also help show how well groups work together, and what types of training are most helpful for improving teamwork.

“Using a non-invasive version of this approach, we may be able to quantify how well professional athletes, musicians or dancers are working together, or if an audience is engaged in what they’re seeing, listening or imagining,” says Nicolelis. “This could be valuable for any social task that requires the synchronization of many individuals to improve social cohesion.”

By Connor Ertz, Staff Writer

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