In a first, scientists including one of Indian origin, have discovered that stimulating the brain during sleep may strengthen memory, a finding that may lead to a non-invasive method to help people with conditions such as autism and Alzheimer's disease.
Scientists at University of North Carolina (UNC) in the US used transcranial alternating current stimulation (tACS) to target a specific kind of brain activity during sleep and strengthen memory in healthy people.
For years, researchers have recorded electrical brain activity that oscillates or alternates during sleep; they present as waves on an electroencephalogram (EEG).
These waves are called sleep spindles, and scientists have suspected their involvement in cataloging and storing memories as we sleep.
"Our study shows that the spindles are crucial for the process of creating memories we need for every-day life. And we can target them to enhance memory," said senior author Flavio Frohlich, assistant professor at UNC.
This marks the first time a research group has reported selectively targeting sleep spindles without also increasing other natural electrical brain activity during sleep.
This has never been accomplished with tDCS - transcranial direct current stimulation - in which a constant stream of weak electrical current is applied to the scalp.
For the study, 16 male participants underwent a screening night of sleep before completing two nights of sleep.
Before going to sleep each night, all participants performed two common memory exercises - associative word-pairing tests and motor sequence tapping tasks, which involved repeatedly finger-tapping a specific sequence.
On both nights, each participant had electrodes placed at specific spots on their scalps.
One of the nights, each person received tACS - an alternating current of weak electricity synchronised with the brain's natural sleep spindles. During the other night, each person received sham stimulation as placebo.
Each morning participants performed standard memory tests.
Researchers, including Sankaraleengam Alagapan, found no improvement in test scores for associative word-pairing but a significant improvement in the motor tasks when comparing the results between the stimulation and placebo night.
"This demonstrated a direct causal link between the electric activity pattern of sleep spindles and the process of motor memory consolidation," Frohlich said.
"We know sleep spindles, along with memory formation, are impaired in a number of disorders, such as schizophrenia and Alzheimer's," said Caroline Lustenberger, postdoctoral fellow at Frohlich lab.
"We hope that targeting these sleep spindles could be a new type of treatment for memory impairment and cognitive deficits," she said.
The study was published in the journal Current Biology.
