0081 Parasympathetic Activity During Sleep, But Not Wake, Facilitates Working Memory Improvement: A Comparison Of Young And Older Adults

Abstract

Introduction: For centuries, the autonomic nervous system (ANS) has been thought to contribute to the processing of emotionally- laden information. More recently, the parasympathetic branch of the ANS has been implicated in executive function, with higher parasympathetic activity during wake associated with better working memory (WM). Compared with wake, sleep is a period with substantially greater parasympathetic tone, and sleep facilitates WM. Yet, the role of this sleep-dependent boost in parasympathetic activity for WM is not known. Methods: 107 young (Age:17-23) and 101 older adults (Age: 60-85) were randomized to either have a 2-hour nap opportunity monitored with polysomnography (PSG) (Young: n=58; Older: n=54) or stay awake (Young: n=49; Older: n=47), where subjects engaged normal daily activities with activity watch monitoring. We tested WM using the Operation-Span task in the morning and evening, and measured autonomic activity, as measured by heart rate variability (HRV), during the inter-test period containing a nap or wake period. To assess the autonomic profiles, we used linear- mixed effect models (LME), with a within-subjects factor of stage (Resting, Stage 2, SWS, REM) and a between-subjects factor of age (Young vs. Older). Results: Our analysis revealed a significant interaction between age and sleep stage, where young adults showed the expected boost in parasympathetic activity during sleep, while older adults showed a marked loss of parasympathetic tone during the nap. Also, young adults demonstrated sleep-dependent WM improvement, which was associated with relative parasympathetic power during sleep. In contrast, older adults showed no beneficial effect of nap and no correlation between parasympathetic activity and WM. Conclusion: Parasympathetic activity during sleep, but not wake, has substantial implications for WM in young adults, but no such cardiovascular break occurs during daytime naps in the elderly.