Sara C. Mednick, psychology professor at the University of California, Riverside, lead a team of sleep researchers to look at the autonomic nervous system (ANS) – the part of the body that is responsible for controlling the unconsciously directed functions such as heartbeat, digestion, and breathing – and the role it plays in memory consolidation in terms of sleep. Memory consolidation is the process of moving information from short- to long-term memory
The title of this groundbreaking study is Autonomic Activity During Sleep Predicts Memory Consolidation in Humans, and has been published in the journal, Proceedings of the National Academy of Sciences. For the first time, researchers discovered that an increase in ANS activity during sleep is directly linked to memory improvement.
Ms. Mednick explained that sleep is known to facilitate the conversion of recent experiences into long-term memory storage; however, previous studies generally had contradictory evidence with regard to which sleep features were responsible for enhancing memory. Ms. Mednick and her team believe this is suggestive of the presence of unidentified events during sleep, which could be playing a large role in the process of memory consolidation and enhancement. ANS activity enhances memory during waking hours, so Mednick decided to test the theory that this ANS activity could be that missing link explaining how memory consolidation is promoted by sleep.
Mednick and her team tested the theory by adding a memory component to a creativity test well-known in the medical community called the Remote Associates Test (RAT). Two sessions were given, and in between sessions, some of the participants were allowed to take a nap. Their sleep quality and heart activity were monitored in this process.
The first part of the study included 81 individuals who were given RAT problems of three unrelated words and were asked to find another word that links them together. Some of the participants completed an analogy task that was completely unrelated. The unrelated analogy task used prime words for solving some of the RAT problems in the second test that was taken after the nap. After the first tasks were completed, only 60 of the participants were allowed to take a 90-minute nap, while the rest watched a video. All participants went back to the lab later in the day to complete the second RAT test, which was completely new.
Comparted to those who did not take a nap, those who did were better able to answer the creativity problems in the afternoon after their nap using words that were primed by the analogy task in the morning. That showed researchers that the nap helped the participants think more clearly and flexibly, with the ability to combine primed words in new and more useful combinations. While REM sleep can predict about 40% of the improvement after napping, when heart rate and activity was considered during REM, researchers were able to account for as much as 73% of performance increases.
Ms. Mednick notes the findings demonstrate that higher ANS activity during sleep is an unexplored aspect to the improvement of memory during sleep. These findings implicate a better understanding of the mind/body connection and the link between heart health, cognitive functioning, and sleep.
Author: Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.