title: Hippocampal activity mediates the relationship between circadian activity rhythms and memory in older adults.
abstract: Older adults experience parallel changes in sleep, circadian rhythms, and episodic memory. These processes appear to be linked such that disruptions in sleep contribute to deficits in memory. Although more variability in circadian patterns is a common feature of aging and predicts pathology, little is known about how alterations in circadian activity rhythms within older adults influence new episodic learning. Following 10 days of recording sleep-wake patterns using actigraphy, healthy older adults underwent fMRI while performing an associative memory task. The results revealed better associative memory was related to more consistent circadian activity rhythms, independent of total sleep time, sleep efficiency, and level of physical activity. Moreover, hippocampal activity during successful memory retrieval events was positively correlated with associative memory accuracy and circadian activity rhythm (CAR) consistency. We demonstrated that the link between consistent rhythms and associative memory performance was mediated by hippocampal activity. These findings provide novel insight into how the circadian rhythm of sleep-wake cycles are associated with memory in older adults and encourage further examination of circadian activity rhythms as a biomarker of cognitive functioning.
authors.affiliation: Department of Psychology, The University of Texas at Austin, 108 E. Dean Keeton A8000, Austin, TX 78712, USA. Electronic address: ssherman@utexas.edu.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Sherman
authors.affiliation: Center for Investigating Healthy Minds at the Waisman Center, University of Wisconsin-Madison, 1500 Highland Avenue, Suite S119, Madison, WI 53705, USA.
authors.forename: Jeanette A
authors.initials: JA
authors.lastname: Mumford
authors.affiliation: Department of Psychology, The University of Texas at Austin, 108 E. Dean Keeton A8000, Austin, TX 78712, USA; The Institute for Neuroscience, The University of Texas at Austin, 1 University Station, C7000, Austin, TX 78712, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Schnyer
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000502:physiology; D001931:Brain Mapping; D002940:Circadian Rhythm; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D061212:Memory, Episodic; D011939:Mental Recall / Q000502:physiology*; D008875:Middle Aged; D012890:Sleep
keywords: Associative memory; Circadian activity rhythms; Hippocampus; Sleep