Study: How Autonomic Nervous System Activity During Sleep Affects Memory Improvement

A new study conducted by sleep researchers from the University of California-Irvine has found a linked between the autonomic nervous system activity during sleep and memory improvement.

The study, published in the journal Proceedings of the National Academy of Sciences, suggests that an increase of autonomic nervous system activity during sleep promotes better memory consolidation, resulting memory improvement.

Autonomic nervous system or ANS is responsible for controlling involuntary bodily functions, such as breathing, heartbeat and digestive process.

Memory Consolidation is the process in which information from the short-term memory are converted into long-term memory.

According to a press release, researchers believe that ANS may play a crucial role in the promotion of memory consolidation during sleep because ANS has the ability to enhance memory during waking hours.

For the study, researchers enrolled 81 healthy individuals. The participants were asked to undertake Remote Associates Tests (RAT). The RAT problems consisted of three seemingly unrelated words and participants were asked to find another word that links the three words together. Some of the participants were also given unrelated analogy task to serve as primes for the second RAT.

After finishing the RAT, 60 participants were asked to take 90-minute nap, while others watched a video. After the nap or the video presentation, the participants were once again asked to take RAT, which now consists of problems either identical to the previous test (repeated condition), completely new (novel condition) or had the same answers as the analogy task (primed condition).

The researchers then found out that the participants who took a nap were more likely to the creativity problems in the afternoon with words that were primed by the morning analogies task compared with people who didn't nap. This suggests that napping may have helped the participants think more flexibly and combine primed words in "new and useful" combinations.

More importantly, the researchers also discovered that about 40 percent of the improved performance after the nap could be predicted by the amount of the rapid-eye movement (REM) during sleep, while 73 percent of the performance increase could be accounted if the heart rate activity was considered during REM.

"The findings suggest that ANS activity during REM sleep may be an unexplored contributor to sleep-related improvements in memory performance," explained Sara C. Mednick, a psychology professor at University of California, Riverside, and lead author of the study, in a statement.