A Different Drummer: Stanford Engineers Discover Neural Rhythms Drive Physical Movement

By Andrew Myers | Sunday, June 3, 2012

Neuroscientists had once believed that the neurons that control movement send specific external information such as distance, direction and velocity to the muscles of the body. In a surprising new finding, however, researchers at Stanford University have proposed a new model that says motor neurons instead send basic rhythmic patterns down the spine to drive movement.

The neurons that control movement are not a predictable bunch. Scientists working to decode how such neurons convey information to muscles have been stymied when trying to establish a one-to-one relationship between a neuron’s behavior and factors such as muscle activity or movement velocity.

In an article published online June 3rd by the journal Nature, a team of electrical engineers and neuroscientists working at Stanford University propose a new theory of the brain activity behind arm movements. Their theory is a significant departure from existing understanding and helps to explain, in relatively simple and elegant terms, some of the more perplexing aspects of the activity of neurons in the motor cortex.

In their paper, electrical engineering Associate Professor Krishna Shenoy and post-doctoral researchers Mark Churchland, now a professor at Columbia, 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.

Understanding the Brain

Neuroscientists have long known that the neurons responsible for vision encode specific, external-world information – the parameters of sight. It had been theorized and widely suggested that motor cortex neurons function similarly, conveying specifics of movement such as direction, distance and speed, in the same way the visual cortex records color, intensity and form.

19th century mathematician Joseph Fourier showed that two rhythms could be summed to produce a third rhythm. Researchers at Stanford have shown that such mathematics are at play in the brain activity that produces arm movements.

“Visual neurons encode things in the world. They are a map, a representation,” said Churchland, who is first author of the paper. “It’s not a leap to imagine that neurons in the motor cortex should behave like neurons in the visual cortex, relating in a faithful way to external parameters, but things aren’t so concrete for movement.”

Scientists have disagreed about which movement parameters are being represented by individual neurons. They could not look at a particular neuron firing in the motor cortex and determine with confidence what information it was encoding.

“Many experiments have sought such lawfulness and yet none have found it. Our findings indicate an alternative principle is at play,” said co-first author Cunningham ...

See the full article A Different Drummer: Stanford Engineers Discover Neural Rhythms Drive Physical Movement.