Relationship between sleep architecture and episodic memory in older adults

Introduction: Normative ageing is associated with alterations in both macro and micro architecture of sleep and a decline in episodic memory. The relationship between sleep architecture and episodic memory is still unclear.

Methodology: Total 75 older adults were recruited for study (59 Male and 16 Female). Polysomnography was done according to American Academy of Sleep Medicine (AASM) criteria and Indian Council of Medical Research-NeuroCognitive Toolbox (ICMR-NCTB) was used for assessing episodic memory. EEG analysis was done in Python. Statistical analyses were done using GraphPad Prism 9.0.0. Correlation was done to see the association between sleep architecture and cognitive functions.

Results: Mean age of the participants was 66 (50-80) years. N2 sleep percentage is positively associated with Montreal Cognitive Assessment (MoCA) score, which measures global cognition (r= 0.38, p=0.001). Sleep efficiency is positively (r= 0.28, p=0.012) associated with spatial recall scores and N2 sleep percentage is positively associated with Modified Taylor Complex Figure (MTCF) immediate (r= 0.43, p=0.000) and delayed recall (r= 0.40, p=0.001), which measures visuo-spatial memory of episodic domain of cognition. Spindle amplitude has a significant positive correlation with delayed recall (r= 0.37, p=0.0009), which measures the verbal memory function of episodic domain. Spindle density has a positive correlation with delayed recall, which measures verbal memory; MTCF delayed and immediate recall, which measures visuo-spatial memory of episodic domain of cognition.

Conclusions: N2 sleep percentage, sleep efficiency, spindle amplitude and spindle density have a significant moderate association with episodic memory. So preservation of above mentioned sleep parameters helps in maintaining episodic memory to some extent in older adults, as their association is moderate.