New research challenges an influential theory regarding population neurodynamics as a fundamental property of the brain.
A new study by researchers at the University of Chicago finds that the dynamics of neurons in the motor cortex are completely different during access to and understanding of behavior, challenging the popular theory that intrinsic dynamic patterns control motor behaviors.
Previous research examining the dynamics of neural assemblies in the motor cortex of macaques has shown that during the planning and execution of arm-linking movement, groups of neurons exhibit rotational dynamics – a series of smooth, orderly waves of neural activity that pass through the motor cortex.
This behavior has been interpreted at the population level as showing that the motor cortex acts as a generator of the pattern that prompts the muscles to induce movements.
“In previous work on access, my colleagues and I showed that areas of the brain that control movement act like a small machine to generate muscle commands,” said co-author Matthew Kaufman, Ph.D., assistant professor of biology and anatomy at the University of Chicago. That is, the activity follows a mathematical “rules” that make it work like a jukebox, to obtain the commands of each muscle at the appropriate time in relation to others.
The researchers suggested that these patterns of activity represent a general principle of neural activity within the motor cortex, and that these elegant dynamics are characteristic of neural circuits.
“The pattern of activity is a bit like the domino effect,” explained senior author Suleiman Bansimia, Ph.D., and James and Karen Frank family professor in biology and anatomy at the University of Chicago. “The idea is that when the behavior starts, it’s like hitting the first domino, and then the rest will fall in order. If I set it up back up, it would do the same sequence again.”
However, this new research, which looks instead at hand-grip rather than arm-reaching behavior, did not see such an elegant pattern. The study was published on November 17th Electronic lifeExamination of nerve activity in the motor cortex.
“We wanted to know if the same type of neurodynamics is present during the hand movements, which involve completely different stimuli, producing very different movements,” said first co-author Anisha Suresh, Ph.D., a former graduate student at Bansimia’s lab. “We recorded neural activity in the monkeys’ motor cortex while they performed an access task and an understanding task to compare the dynamics of the two movements.”
In contrast to previous results, the researchers found that internalization of behaviors instead produced less structured neuronal activity patterns at the population level and little evidence of rotational dynamics seen upon access to the movements.
Senior co-author James Goodman, Ph.D., is now a post-doctoral scientist at the German Primate Center. “Instead, the activity patterns that we saw while gripping were more complex and messy, suggesting in some ways a particularly important role for the sense of touch and the sense of the body during hand movements.”
These results make sense in the context of the differences between access to movements and grip. “Conceptually, the functions that the arm performs are different from the hand,” said co-author Nicholas Hatsopoulos, Ph.D., professor of biology, anatomy and neuroscience at the University of Chicago. “The arm moves the hand and brings the hand to different locations for actions such as waving or reaching out for a cup. On the other hand, the hand is usually involved in manipulating things like grasping objects, typing on the keyboard, etc.”
This study raises new questions, such as why this elegant activity pattern exists to access movements but not to grasp them, and whether similar patterns exist for other types of movement patterns. Bansameya said: “The brain uses this type of pattern to access it, and the result was that the brain will use it in other movements as well, and this pattern may even apply in other systems.” “But we showed that this pattern isn’t universalized everywhere, and then the question is, how general is it, really?”
The study, “Neural population dynamics in the motor cortex in terms of access and understanding”, was supported by NINDS grants NS082865, NS101325, NS096952, NS045853, and NS111982. Elizaveta Okurokova from the University of Chicago is also an author.
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Alison Caldwell, PhD
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