Mark Churchland and colleagues at Stanford University in California, US, made the discovery after training macaque monkeys to repeat a simple reaching task thousands of times. "The nervous system was not designed to do the same thing over and over again," Newscientist quoted Churchland as saying. The team of scientists showed the monkeys a coloured spot and rewarded them for reaching out to touch it at different speeds.
During the exercise, they monitored the promoter cortex of the monkeys' brains, which is the region responsible for movement planning, and tracked the speed of the resulting motion. Over the course of thousands of reaches, the monkeys rarely moved with exactly the same speed. Small variations in reach speed followed small variations in brain activity during movement planning, the researchers say.
Contrary to conventional wisdom that movement variability is caused by muscle activity, the team found that neural activity accounts for about half the variations. In other words, training muscles to perform a certain way through practice, such as countless hours teeing off or shooting a basketball, will not produce the same shot every time because the brain's behaviour is inconsistent. The researchers speculate that humans and animals evolved with this "improvisational style" in response to the predator-prey dynamic where predators never catch and kill prey in exactly the same conditions.
"Premium athletes' quest for consistency is a stark contrast to the way we evolved through history," said Shenoy. The team hopes that understanding the way the brain controls movement may lead to treatments for neurological conditions such as Parkinson's disease, which is characterised by tremors.
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