Motor Cortex Synchronicity Levels Influenced By Proximity & Social Status


Scientists have previously shown that when one animal watches another performing a motor task, such as reaching for food, so-called mirror neurons in the motor cortex of the observer’s brain start firing as though the observer were also reaching for food.

New research from Duke University suggests mirroring in monkeys is also influenced by social factors, such as proximity to other animals, social hierarchy and competition for food.

The Duke team found that when pairs of monkeys interacted during a social task, the brains of both animals showed episodes of high synchronization, in which pools of neurons in each animal’s motor cortex tended to fire at the same time. This phenomenon is known as interbrain cortical synchronization.

“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,”

said senior author Miguel Nicolelis, M.D., Ph.D.

Simultaneous Neural Recording

Previously, neuroscientists had limited their studies to recording brain activity in one animal at a time. What makes this research unique, Nicolelis said, is that the Duke team created a multi-channel wireless system to record the electrical activity of hundreds of neurons in the motor cortices of two monkeys simultaneously as they interacted in the same space.

During one task, one monkey, called the passenger, sat in an electronic wheelchair programmed to reach a reward across the room, a fresh grape. A second monkey, the observer, was also in the room watching the first monkey’s trajectory toward the reward.

Interbrain cortical synchronization during navigation
Interbrain cortical synchronization (ICS) during the navigation task. (A) Locations of cortical implants in three monkeys (C,J, and K). Neuronal-ensemble recordings were conducted in M1 (red dots) and PMd (blue dots), in both hemispheres. (B) The experimental setup. Two monkeys (passenger and observer) were placed in a 5.0-by-3.9 m room. The passenger sat in an electrically actuated wheelchair. The observer sat in a stationary chair placed in the corner of the room. During each trial, the passenger moved from a starting location (shown on the left) to a stationary grape dispenser. Five representative routes of the wheelchair are plotted in different colors. These routes were randomly generated by a computer program. (C) Color plots of neuronal-ensemble activity for two representative trials. Each horizontal line corresponds to a unit. Color represents normalized (z-scored) firing rate of 69 units were recorded in monkey C (observer in this experiment) and 47 in monkey K (passenger). Episodes of ICS are marked by red horizontal lines. (D) Continuous evaluation of ICS for the trials shown in (C). Instantaneous values of the distance correlation were computed with a sliding window, of the same 3-s width as the red bars in (C). Correlation peaks are marked by arrows. (E) Wheelchair routes for the same trials as in (C) and (D). The routes are color-coded to indicate ICS. Credit: Po-He Tseng, et al. CC-BY

Electrical activity in the motor cortex of each monkey’s brain was recorded simultaneously. An analysis showed that when the passenger traveled across the room under the attentive gaze of the observer, pools of neurons in their motor cortices showed episodes of synchronization.

The researchers found these episodes of interbrain cortical synchronization (ICS) could predict the location of the passenger’s wheelchair in the room, as well its velocity. The brain activity could also predict how close the animals were to each other, as well as the passenger’s proximity to the reward.

Interbrain Cortical Synchronization

The most compelling finding, they said, was that ICS could predict another key social parameter – the rank of the monkeys in the colony.

During tasks when the colony’s most dominant monkey was traveling toward the reward under the observation of a lower-ranking animal, the magnitude of ICS grew steadily as the passenger approached the observer. Synchronization peaked when the animals were about three feet apart – close enough that one might be able to stretch out an arm to groom the other, or attack.

But when a lower-ranking monkey was the passenger and the dominant monkey was observing, ICS did not increase as the monkeys got closer, suggesting social rank plays a role in brain synchronization.

The researchers believe episodes of ICS were generated by the simultaneous activation of mirror neurons in both the passenger’s and observer’s brains. They propose similar correlations between brain synchrony and social interaction might take place during human social interactions, as well.

Potential Implications

The findings could lead to new diagnostics or treatments for conditions where neuronal mirroring might not follow typical patterns, as has been suggested in autism, they said. Measuring ICS in humans could also reveal how well groups work together, and even what types of training improve their brain synchrony and 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,” Nicolelis said. “This could be valuable for any social task that requires the synchronization of many individuals to improve social cohesion.”

Nicolelis plans to explore brain synchrony in people through future trials at Duke using functional MRI and electrode caps.

The study was supported by The Hartwell Foundation, and the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health, both part of the National Institutes of Health.

Reference: Po-He Tseng, Sankaranarayani Rajangam, Gary Lehew, Mikhail A. Lebedev, Miguel A. L. Nicolelis. Interbrain cortical synchronization encodes multiple aspects of social interactions in monkey pairs. Scientific Reports volume 8, Article number: 4699 (2018) doi:10.1038/s41598-018-22679-x

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Last Updated on December 12, 2022