Electrical engineers and neuroscientists at Stanford University have proposed a new theory of the brain activity behind arm movements in an article published online June 3rd by "Nature".
Neuroscientists have long known that the neurons responsible for vision encode specific, external-world information in a form resembling digital electronic video. Many neuroscientitsts thought that motor cortex neurons transmitted signals about direction, distance, and speed, in the same way visual cortex neurons transmit color, intensity, and form.
The co-first author of the study Mark Cunningham said that "Our findings indicate an alternative principle is at play ... the motor cortex is a flexible pattern generator, which sends rhythmic signals down the spinal cord".
The researchers studied the brain activity of monkeys reaching to touch a target. By monitoring the electrical activity of motor-cortex neurons in the monkeys, researchers found an oscillatory response that is not independent from neuron to neuron. Instead, the entire neural population oscillates as one. The electrical signal that drives a given movement is the summation of the rhythms of all the motor neurons firing at a given moment.
"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."
Mr. Churchland explained that the patterns of activity the primary motor cortex displays presumably derive from evolutionarily older rhythmic motions such as the swimming motion of leeches and the gait of walking monkeys.
"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."
"Finding these brain rhythms surprised us a bit, as the reaches themselves were not rhythmic. In fact, they were decidedly arrhythmic, and yet underlying it all were these unmistakable patterns," said Churchland.
"Further research in this area may help us devise more effective technology for controlling prosthetic limbs." said Yuan Liu of NIH.
I think this is very cool and that scientists and engineers can turn this work into thinks that can help suffering humanity as fast as possible. I also think it confirms an older artistic insight into music and dance:
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