In a new study, researchers investigated the association between sleep, cognitive reserve and cognition in older adults.
Sleep is vital for our health and well-being, but as we age, we tend to experience less and less of it. In particular, we lose some of the deep sleep stages, known as slow wave sleep (SWS), that are crucial for memory consolidation and brain maintenance. This can affect cognitive performance and increase our risk of developing dementia.
Not everyone is equally vulnerable to the negative effects of poor sleep quality. Some people seem to be more resilient and able to cope with less SWS without compromising their mental abilities. What makes them different? One possible factor is cognitive reserve (CR).
CR is a concept that refers to the brain’s ability to adapt and compensate for age-related changes or brain damage. It is influenced by various aspects of our life experiences, such as education, occupation, leisure activities, social interactions, and mental stimulation. People with higher CR are thought to have more efficient brain networks, more cognitive strategies, and more brain reserve (i.e., more neurons and connections) that can buffer the impact of aging or pathology on cognition.
In a new study, researchers Valentin Ourry, Stéphane Rehel, Claire André, Alison Mary, Léo Paly, Marion Delarue, Florence Requier, Anne Hendy, Fabienne Collette, Natalie L. Marchant, Francesca Felisatti, Cassandre Palix, Denis Vivien, Vincent de la Sayette, Gaël Chételat, Julie Gonneaud, and Géraldine Rauchs from Normandie University, UNI – ULB Neuroscience Institute, University of Liege, University College London, and CHU de Caen aimed to identify individuals in whom sleep disturbances might have greater behavioral consequences. On September 28, 2023, their research paper was published in Aging’s Volume 15, Issue 18, entitled, “Effect of cognitive reserve on the association between slow wave sleep and cognition in community-dwelling older adults.”
The researchers investigated whether CR could modulate the association between SWS and cognition in older adults. The researchers recruited 135 cognitively intact older adults (mean age: 69.4 years) from the Age-Well randomized controlled trial and measured their sleep quality using polysomnography — a technique that records brain waves, eye movements, muscle activity, and other physiological signals during sleep. They also assessed their cognitive performance using neuropsychological tests that evaluated executive function (i.e., the ability to plan, organize, monitor, and control one’s behavior) and episodic memory (i.e., the ability to remember personal events and experiences).
To estimate CR, the researchers used two measures of cognitive engagement throughout life: a questionnaire that asked about the frequency and diversity of participation in various activities (such as reading, playing games, learning languages, etc.) in different age periods; and a composite score based on the highest level of education attained, the complexity of the main occupation held, and the current cognitive activity level.
The results showed that SWS was positively associated with episodic memory performance, meaning that participants who had more SWS tended to have better memory scores. However, this association was not observed for executive function performance. CR proxies modulated the associations between SWS and both executive and episodic memory performance. Specifically, participants with higher CR were able to maintain cognitive performance despite low amounts of SWS, whereas participants with lower CR showed a steeper decline in performance as SWS decreased.
“This study provides the first evidence that CR may protect against the deleterious effects of age-related sleep changes on cognition.”
The study suggests that engaging in cognitively stimulating activities throughout life may enhance one’s ability to cope with less SWS without compromising one’s mental abilities. It also highlights the importance of considering individual differences in CR when evaluating the impact of sleep quality on cognition in older adults.
The authors were forthcoming about limitations of their study, such as the cross-sectional design that does not allow causal inferences, the relatively small sample size that limits the generalizability of the findings, and the use of proxy measures that may not capture all aspects of CR. They also point out some directions for future research, such as exploring the underlying mechanisms of how CR influences sleep-cognition relationships, examining whether CR can also modulate the effects of other sleep parameters (such as sleep duration or fragmentation) on cognition, and investigating whether interventions that target sleep quality or CR can improve cognitive outcomes in older adults.
In conclusion, this study suggests that CR may be an important factor that can help us sleep better and think sharper as we age. It also encourages us to keep our brains active and challenged throughout our lives, as this may benefit not only our cognitive functioning but also our sleep quality.
“These findings are important to understand the factors promoting successful aging and suggest that the deleterious impact of sleep disturbances could be counteracted by an enriched lifestyle. This will help to design non-pharmacological interventions to promote successful aging and counter age-related sleep changes.”
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