Have you ever fallen asleep desperately trying to remember something, only to wake up in the morning with the memory readily available to you? No, it’s not just you this has happened to — and nor is it a fluke. In fact, a new research project by South Korea’s Institute for Basic Science’s Center for Cognition and Sociality builds on the insight that a good night’s sleep can help us remember what we have studied or experienced the day before.
In doing so, researchers have discovered that the triggering of specific brain waves during sleep can almost double long-term memory. Although, sadly, it’s not available to humans just yet.
Previous studies have shown that several brain rhythms — cortical slow wave, thalamic spindle, and hippocampal sharp-wave-ripples (SWR) — take place during sleep, and that these are involved in memory consolidation. These phases of sleep alternate with REM sleep, which is associated with dreaming. The researchers focused on spindles, which come from a part of the brain called the thalamic reticular nucleus, and spike at a rate of around seven to 15 per second. The number of spindles increases after a day with plenty of learning and also decline in elderly people — suggesting a strong link with memorization.
In an experiment, mice were implanted with a fear memory by putting them in a special cage and then giving them a mild electric shock after playing atonal noise. The day after this was done, the mice had their memories tested by seeing how they responded to either the cage or the same noise. By using different levels of light stimulations on the mice the night before the test, the researchers were able to manipulate the number of overnight spindles — thereby either increasing or reducing memory of the fear memory.
“The results were dramatic,” Dr. Hee-Sup Shin, director of the Center for Cognition and Sociality, told Digital Trends. “Inducing extra amount of spindles in the brain during sleep after fear conditioning helped the mice remember better the fear memory, twice as strongly, when assayed next day. Importantly, only the group of mice that received spindle induction in-phase with cortical slow waves revealed enhanced memory, while the two control groups did not.”
Long-term, the hope is that the work could be used for brain-training in humans. “In the current experiments done in the mouse, we use optogenetic tools which involve expressing a foreign gene and implanting an optic cable in the thalamic reticular nucleus of the mouse,” Shin said. “These tools may not be used for humans. In the future, however, when non-invasive tools are developed for manipulating brain rhythms in humans, a similar approach may be tried in humans to improve memory for whatever purposes.”