A daytime nap restores hippocampal function and improves declarative learning. Issue 9 (28th March 2020)

• Record Type: Journal Article
• Authors: Ong, Ju Lynn; Lau, Te Yang; Lee, Xuan Kai; van Rijn, Elaine; Chee, Michael W L
• Is Part Of: Sleep. Volume 43:Issue 9(2020)
• Publication Date: 2020-03-28
• Subjects: daytime nap -- sleep spindles -- slow oscillations -- hippocampus -- declarative learning; Sleep -- Physiological aspects -- Periodicals; Sleep disorders -- Periodicals; Sommeil -- Aspect physiologique -- Périodiques; Sommeil, Troubles du -- Périodiques; Sleep disorders; Sleep -- Physiological aspects; Sleep -- physiological aspects; Sleep Wake Disorders; Psychophysiology; Electronic journals; Periodicals; 616.8498
• DOI: 10.1093/sleep/zsaa058
• Languages: English
• ISSNs: 0161-8105

Abstract

Abstract: Study Objectives: Daytime naps can confer benefits on subsequent declarative learning, but the physiological correlates of this improvement are less well studied. We examined learning following a daytime nap compared with an equivalent waking period using fMRI and polysomnography. Methods: Forty healthy young adults who slept normally the previous night encoded word pair lists in an MRI scanner at 13:00 and 16:30. Between sessions, participants either stayed awake and watched a documentary (Wake Group; N = 20) or had a 90-minute nap opportunity (Nap Group; N = 20) monitored by polysomnography. Approximately 40 minutes after completing each encoding session, memory for learned words was assessed using cued-recall. Results: A significant Session × Group interaction effect ( p < 0.001) was observed in which memory was significantly improved in the Nap but not in the Wake group ( p < 0.001). There was also a Session × Run × Group interaction effect in the left hippocampus ( p = 0.001), whereby activation during word pair encoding increased only following the nap. Both performance improvement ( r s = 0.46, p = 0.04) and nap-related increase in hippocampal activation ( r s = 0.46, p = 0.04) were correlated with nap spindle count (12–15 Hz) but not with slow oscillation power ( p 's ≥ 0.18). Conclusions: After a habitual nocturnal sleep, participants who had a 90-minute afternoon nap encoded word pairs better than a comparable group who stayed awake. Increases in hippocampal activation following the nap suggest restored hippocampal function. Naptime spindles may contribute to improved memory.