Use of electrical brain stimulation can enhance memory during sleep and strengthen memory in healthy people, says a study.
According to the researchers, transcranial alternating current stimulation (tACS) is a non-invasive method that can potentially help millions of people with conditions such as autism, Alzheimer's disease, schizophrenia and other major depressive disorders.
For years, researchers have recorded electrical brain activity that oscillates or alternates during sleep, which presents itself as waves on an electroencephalogram (EEG). These waves are called sleep spindles and scientists have suspected their involvement in cataloguing and storing memories as we sleep.
The researchers, for this study, have reported selectively targeting sleep spindles -- burst of oscillatory brain activity visible on an EEG -- without also increasing other natural electrical brain activity during sleep.
This has never been accomplished with tDCS - transcranial direct current stimulation where a constant stream of weak electrical current is applied to the scalp.
"Our study shows that, indeed, 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 Flavio Frohlich, Researcher at the UNC School of Medicine.
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For the study, 16 male participants underwent a screening night of sleep before completing two nights of sleep for the study.
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.
During both study nights, each participant had electrodes placed at specific spots on their scalps. During sleep at night, each person received tACS -- an alternating current of weak electricity synchronized with the brain's natural sleep spindles.
During sleep the next night, each person received sham stimulation -- an inactive form of stimulation (very brief or weak one) that is used in research to control -- as placebo.
Each morning, researchers had participants perform the same standard memory tests. They 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," added Frohlich in the work published in the journal Current Biology.
The researchers previously used tACS to target the brain's natural alpha oscillations to boost creativity. This was a proof of concept.
It showed it was possible to target these particular brain waves, which are prominent as we create ideas, daydream, or meditate. These waves are impaired in people with neurological and psychiatric illnesses, including depression.
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