By Victoria Gill
Science reporter, BBC News
Brain waves appear to have a direct effect on behaviour
Researchers have used electrodes to make people move in slow motion.
The scientists "boosted" human subjects' brain waves - applying a small alternating current via electrodes on the volunteers' scalps.
These waves are patterns generated naturally by groups of neurons, or brain cells, firing in a rhythm.
In the journal Current Biology, the researchers described how their finding shows that brain waves directly affect human behaviour.
The results also reveal clues about movement disorders, such as Parkinson's disease, sufferers of which have difficulty making voluntary movements.
Lead author Professor Peter Brown, from University College London in the UK, said: "We induced the same patterns as you see in normal brains via electrodes."
He and his team boosted one specific form of relatively low frequency brain wave called a beta oscillation.
"Different parts of the brain work together and generate certain frequencies," he explained, "and the movement areas of the brain come together in beta activity.
"That activity is suppressed just prior to and during movement, so we think the body gets rid of it to prepare to make a new movement."
Boosting beta brain waves slowed people's movement by 10%
To investigate the effect of this beta activity, the research team gave healthy human subjects electrical stimulation through their scalps.
"The currents we use are very small... but [they] shape the likelihood of neurons firing in the imposed rhythm," he told BBC News.
During the test each volunteer was shown a dot on a computer screen. They were able to control another marker on the same screen with a joystick.
"The dot jumped to a new location and when they were signalled to by an alarm they had to move [their marker] to that new location as quickly as they could," Professor Brown explained.
"When we applied the beta stimulation that quick movement was slowed by 10%.
"So we have a direct experiment showing a causal link between the oscillations and the behaviour," he said.
Professor Brown explained that beta activity was important in Parkinson's disease.
"So this information is very helpful," he said. "Since we've shown that this slows people down, it tells us what Parkinson's disease treatments should be trying to suppress."
Professor John Stein, a neuroscientist from the University of Oxford pioneered the theory of what he refers to as a "beta straitjacket" - a pattern of brain activity that prevents Parkinson's disease patients from making voluntary movements.
"The theory is that... in Parkinson's disease when people try to move they cannot suppress beta [brain waves] and therefore cannot move," he told BBC News.
"This study is the first to show... in normal subjects that beta activity actually slows movement. This supports a causal role for [the] activity in causing a fixed posture and tending to prevent voluntary movements."