Reaching out to touch an object is a simple task, but how our brain coordinates that movement has proved tricky for scientists to decipher. Scientists investigating this puzzle have traditionally based their theories on the way the brain's visual cortex deals with color, intensity and form. But now researchers propose a new theory for physical movement, one based on rhythmic patterns.
A team of electrical engineers and neuroscientists based at Stanford linked coordinated patterns of activity in groups of neurons to movements in shoulder muscles.
The team, led by electrical engineer Krishna Shenoy, PhD, studied brain activity in monkeys reaching to touch a target. The patterns they observed could be explained by summing two simple rhythms, they report (subscription required) in a recent issue of Nature. The neurons did not fire in isolation, but in a kind of concert. A story published today in the Stanford Report explains:
"Under this new way of looking at things, the inscrutable becomes predictable," said [first author Mark Churchland, PhD, now a professor at Columbia]. "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."
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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.
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