Brain Stimulation While Asleep May Boost Memory

Researchers are reporting – for the first time – that a type of brain stimulation during sleep may strengthen memory in healthy people, and they also hope this method can potentially help others with memory impairment as well.

While you sleep, your brain is busy storing and consolidating things learned that day to be retrieved from your memory tomorrow, next week or next year.  For many people, especially those with neurological conditions, memory impairment can be a debilitating symptom that affects everyday life in profound way.

But now, for the first time, scientists at UNC School of Medicine in Chapel Hill, N.C. report using a certain type of brain stimulation, called transcranial alternating current stimulation (tACS), to target a specific kind of brain activity during sleep and strengthen memory in healthy people.  They also hope this method will offer a non-invasive way to potentially help millions of people with conditions such as autism, Alzheimer’s disease, schizophrenia, and major depressive disorder.

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.  But they didn’t know if these spindles were actually involved in the storing and consolidation of memories or were just byproducts of other brain processes that were involved.

The researchers designed an experiment in which 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 one of the nights, each person was given tACS — an alternating current of weak electricity synchronized with the brain’s natural sleep spindles. During sleep the other night, each person received sham stimulation as placebo.

Each morning, researchers had participants perform the same standard memory tests.  The team 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.

We’re excited about this because we know sleep spindles, along with memory formation, are impaired in a number of disorders, such as schizophrenia and Alzheimer’s. We hope that targeting these sleep spindles could be a new type of treatment for memory impairment and cognitive deficits,” says Dr. Caroline Lustenberger, the first author of the study, which appears in Current Biology.