Such was the finding of a study from the University of California-Riverside (UCR), published in theĀ Proceedings of the National Academy of Sciences.The study shows that increase in activity of the autonomic nervous system (ANS) during sleep is strongly linked to memory improvement.The ANS is the part of the nervous system responsible for body functions that are not controlled consciously, such as heartbeat, breathing, and digestion.Senior author Sara C. Mednick, a professor of psychology at UCR, explains the background to the study:"Sleep has been shown to facilitate the transformation of recent experiences into long-term, stable memories. But, past studies produced contradictory evidence about which specific sleep features enhance memory performance."She and her colleagues concluded this meant something as yet unidentified is going on during sleep to promote memory consolidation.They hit on the idea of the ANS because there is evidence that memory during waking hours improves when the ANS is active. As such, they devised a study to test whether ANS activity during sleep could be the missing link that explains how sleep helps memory consolidation.