DISCUSSION AND CONCLUSION
sleep disturbances, AD, dementia
PATHOLOGY
In this study, we assessed the association between SWS and cognition in a cohort of cognitively unimpaired older adults and examined whether CR, assessed using different proxies reflecting mental activities over the life-course, could modulate these links. Our results show that the association between SWS and executive function and episodic memory performance differs according to CR, and this result seems more robust when considering the practice of cognitive/mental activities during mid-life.Our analyses showed a positive, yet not robust, association between the proportion of SWS and episodic memory, while no association was found with executive performance. These findings support the major role of this sleep stage in memory processes [Interestingly, we found that the moderating effects of CR were observed only in women. Considering that several studies have shown greater cognitive resilience against AD pathology or age-related changes in women than in men [Our study has several strengths. Analyses were conducted in a large sample of older participants who underwent a detailed cognitive assessment and polysomnography, the gold-standard for an objective sleep assessment. We also combined a classically used CR proxy (education) and more fine-grained proxies reflecting the exposure to stimulating activities over the life-course. The cognitive assessment included several tasks allowing us to investigate both executive functioning and episodic memory, particularly relevant as they are known to be sensitive to aging and dementia. Finally, most of the findings remained significant after applying FDR correction. Nonetheless, we could only partially replicate our findings when controlling for or splitting individuals according to their AHI. It could be due to a reduced sample size or collinearity in the model controlling for AHI (i.e., AHI and SWS are correlated, r = −0.3, We showed, for the first time in a large sample of older adults, that individuals with a higher CR were able to maintain good executive and episodic memory performance even in case of low amounts of SWS measured objectively by polysomnography. In contrast, older adults with a low CR were more vulnerable to SWS reduction and showed poor cognitive performance. These results suggest that CR may protect against the negative effect of sleep changes in older-age on cognitive performance, and that mid-life could be a potential period of interest which remains to be further investigated in prospective studies. 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.