It may someday be possible to send weak currents of electricity through the scalp during sleep to help improve memory for motor tasks, researchers say.

Results of a small study suggest that enhancing electrical brain waves known as sleep spindles may improve "motor memory," which is what enables people to remember how to walk, ride a bike, and perform other routine movements without having to consciously think about them.

"The results are really exciting, but it's not yet ready to be done at home," said senior author Flavio Frohlich of the University of North Carolina at Chapel Hill.

"The results need to be replicated before we can move forward," Frohlich told Reuters Health.

The function of sleep spindles - short bursts of electrical activity in the brain that happen periodically between light and deep sleep - has not been clear, Frohlich and his colleagues write in Current Biology.

The research team studied 16 men over three nights of sleep. One night was used for an initial screening and the other two for the experiment.

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Before falling asleep each night, the men completed word-pairing tests and motor sequencing tests, which involved repeatedly finger-tapping a specific pattern.

During the experiment, each man had electrodes placed on his scalp. On one night, those electrodes delivered through-the-skull alternating current stimulation, a very weak alternating current of electricity synchronized with the brain's natural sleep spindles. On the second night, there was no electrical stimulation, and the results were used for comparison.

Each morning, the men performed the same word-pairing and finger-tapping exercises.

There were no side effects of the stimulation, Frolich said, and participants were unable to tell whether the previous night had been a stimulation night or a placebo night.

Word-pairing performance was the same regardless of electrical stimulation, but performance on the motor task was better after nights of electrical stimulation, the researchers found.

"This is a fundamental discovery from the perspective of understanding how the brain works," and what sleep spindles do, he said. "Specific electric activity in the brain mediates certain cognitive processes."

It's possible that someday, this type of stimulation could also restore some cognitive functions for people with memory impairment, but it's too soon to answer this question, he said. It's also not clear how long the effects of stimulation last, given that this was a two-day intervention, he said.