Rhythmic Nature of Brain Activity Slowly Unfolds

In monitoring electrical brain activity of motor-cortex neurons, researchers found that they typically exhibit a brief oscillatory response. These responses are not independent from neuron to neuron. Instead, the entire neural population oscillates as one in a beautiful and lawfully coordinated way.

The electrical signal that drives a given movement is therefore an amalgam—a summation—of the rhythms of all the motor neurons firing at a given moment.

"Under this new way of looking at things, the inscrutable becomes predictable," said Churchland. "Each neuron behaves like a player in a band. When the rhythms of all the players are summed over the whole band, a cascade of fluid and accurate motion results."

...electrical engineering associate professor Krishna Shenoy and postdoctoral researchers Mark Churchland, now a professor at Columbia University, and John Cunningham of Cambridge University, now a professor at Washington University in Saint Louis, have shown that the brain activity controlling arm movement does not encode external spatial information—such as direction, distance, and speed—but is instead rhythmic in nature. _R&D Mag

This finding, (Nature, June 3, 2012, doi:10.1038/nature11129), is apparently quite startling to a select group of cognitive psychologists who are not well grounded in biology. For Al Fin cognitive scientists, on the other hand, the rhythmic nature of brain activity -- motor, sensory, and higher order activity -- has always been axiomatic.

The specific rhythms associated with particular brain functions will need to be worked out. The Stanford study helps in this regard, with respect to motor cortex rhythms controlling body motion.

In a series of striking graphs, the Stanford team plotted the signals from individual neurons in the motor-cortex as monkeys completed a series of reaches. The reaching motions are shown by the starburst patterns at the top left of each graph. The neuronal patterns are then plotted atop one another for the entire series of reaches, clearly establishing the rhythmic nature of the brain activity. Credit: Mark Churchland, Stanford School of Engineering

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When they monitored the electrical activity of motor-cortex neurons, researchers found that they typically oscillate briefly, not independently as single neurons, but as an entire neural population in one beautifully coordinated way. "Each neuron behaves like a player in a band," said Churchland. "When the rhythms of all the players are summed over the whole band, a cascade of fluid and accurate motion results." The electrical signal for a movement is the sum of the rhythms of all the motor neurons firing at a given moment.

Rhythmic neural activity has been known for a while. It is present in the swimming motion of leeches and the gait of a walking monkey, for instance.

The engineers studied the brain activity of monkeys reaching to touch a target. The pattern of shoulder-muscle behavior could always be described by the sum of two underlying rhythms. "Say you're throwing a ball. Beneath it all is a pattern. Maybe your shoulder muscle contracts, relaxes slightly, contracts again, and then relaxes completely, all in short order," explained Churchland. "That activity may not be exactly rhythmic, but it can be created by adding together two or three other rhythms. Our data argue that this may be how the brain solves the problem of creating the pattern of movement." _Atlantic

The dominant, dysfunctional perspective of machine-oriented cognitivists, who attempt to think of the brain as a mechanical construct -- instead of the evolved organ within a larger organism that it is -- has slowed discovery in cognitive science unnecessarily.

Here is another look at this research:

In the new model, a few relatively simple rhythms explain neural features that had confounded science earlier.

"Many of the most-baffling aspects of motor-cortex neurons seem natural and straightforward in light of this model," said Cunnigham.

The team studied non-rhythmic reaching movements, which made the presence of rhythmic neural activity a surprise even though, the team notes, rhythmic neural activity has a long precedence in nature. Such rhythms are present in the swimming motion of leeches and the gait of a walking monkey, for instance.

"The brain has had an evolutionary goal to drive movements that help us survive. The primary motor cortex is key to these functions. The patterns of activity it displays presumably derive from evolutionarily older rhythmic motions such as swimming and walking. Rhythm is a basic building block of movement," explained Churchland. _PO

Perhaps now, more cognitivists will take this hard-earned insight, and apply it to associative and higher order brain activity. For too long, graduate students and their advisors have struggled under the "single neuron" and "segregated parameters and functions" delusion of brain activity, memory, and control -- perhaps as a confused, erroneous subconscious analogy to computer memory and computer processors.

It is somewhat paradoxical that this important clarification would be made, at least in part, by electrical engineers. It illustrates the importance of multi-disciplinary cooperation in complex fields of research. The real world, it seems, has not been informed that it should hold all its parts within the artificial confines of human academic fields.