High-frequency brain wave patterns in the motor cortex can predict an upcoming move

High-frequency brain wave patterns in the motor cortex can predict an upcoming move

Nicholas G. Hatsopoulos, PhD, Professor of Biology and Anatomy of Organisms at the University of Chicago, has been interested in space for a long time. Specifically, the physical space that the brain occupies.

“Inside our heads, the brain is all crumpled up. If you were to flatten the human cortex into a single 2D sheet, it would cover two and a half square feet of space, about the size of four sheets of paper. You’d think the brain would take advantage of all that space. by organizing activity patterns, but apart from knowing that one part of the brain controls the arm and another part controls the leg, we’ve mostly been ignorant of how the brain might use that spatial organization.”

Now, in a new study published January 16 in Proceedings of the National Academy of Sciences, Hatsopoulos and his team have found evidence that the brain does indeed use the spatial organization of high-frequency propagating waves of neural activity during movement.

The presence of propagating waves of neural activity has been well established, but they are traditionally associated with an animal’s general behavioral state (such as awake or asleep). This study is the first evidence that spatially organized recruitment of neural activity across the motor cortex can inform the details of planned movement.

The team hopes the work will help inform how researchers and engineers decode motor information to build better brain-machine interfaces.

For the study, the researchers recorded the activity of multiple electrode arrays implanted in the primary motor cortex of macaque monkeys while the monkeys performed a task that required them to move a joystick. Next, they looked for wave-like patterns of activity, specifically those of large amplitude.

“We focused on signals from the high-frequency band given their rich information, ideal spatial range, and ease of obtaining the signal at each electrode,” said Wei Liang, the study’s first author and a graduate student in Hatsopoulos’ lab.

They found that these propagation waves, made up of the activity of hundreds of neurons, traveled in different directions across the cortical surface depending on the direction in which the monkey pushed the joystick.

“It’s like a series of falling dominoes,” Hatsopoulos said. “All the wave patterns we’ve seen in the past didn’t tell us what the animal was doing, it would just happen. This is very exciting because now we’re looking at this wave pattern propagating and we’re showing that the direction in which the wave says something about what the animal is about to do.”

The results provide a new way of looking at cortical function. “This shows that space does matter,” Hatsopoulos said. “Rather than just looking at what populations of neurons do and care about, we’re seeing that there are spatially organized patterns that carry information. This is a very different way of thinking about things.”

The research was challenging due to the fact that they were studying the activity patterns of individual movements, rather than averaging the recordings over repeated trials, which can be quite noisy. The team was able to develop a computational method to clean the data to provide clarity on the signals being recorded without losing important information.

“If you average the trials, you lose information,” Hatsopoulos said. “If we want to implement this system as part of a brain-machine interface, we can’t average the tests: your decoder has to do it on the fly, as motion occurs, for the system to work effectively.”

Knowing that these waves contain information about movement opens the door to a new dimension of understanding how the brain moves the body, which in turn may provide additional information for computational systems that will drive brain-machine interfaces of the future.

“The spatial dimension has been mostly ignored until now, but it’s a new angle we can use to understand cortical function,” Hatsopoulos said. “When we try to understand the computations that the cortex performs, we need to consider how neurons are spatially distributed.”

Future studies will examine whether similar wave patterns are seen in more complicated movements, such as sequential movements rather than simply reaching from one point to another, and whether electrical brain stimulation in waveforms can bias the monkey’s movement.

The study, “The propagation of spatiotemporal activity patterns across the macaque motor cortex carries kinematic information,” was supported by the National Institutes of Health (R01 NS111982). Other authors include Karthikeyan Balasubramanianb and Vasileios Papadourakis of the University of Chicago.

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