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Effect of sleep-wake habits on cognitive ageing and on functional compensation : an interventional approach

Year: 2025
Type: dissertation
Study design: Clinical Trial
Abstract: Ageing is accompanied by profound but highly heterogeneous changes in cognition, brain structure and function, and sleep-wake regulation.While some older adults maintain stable trajectories, others exhibit marked decline.Theoretical models of compensation and cognitive reserve suggest that lifelong resources and neural reorganisation support performance until resource limits are reached.These resources are, however, plastic and vary across individuals.Behavioural interventions may therefore modulate ageing trajectories, opening opportunities to preserve performance and delay decline.Yet, why some individuals preserve compensatory efficiency whereas others fail remains an open question.Sleep-wake habits, and in particular daytime napping, represent a promising but understudied factor.Napping increases with age, reflecting both circadian and homeostatic vulnerabilities, yet it may simultaneously blunt sleep-wake consolidation and undermine circadian integrity.This thesis explored whether habitual napping is either a cause, a consequence or both, of circadian dysregulation, and whether this positions it as an active driver of cognitive decline.We further wanted to assess whether acting on this behaviour could modulate cognitive and brain trajectories.An interventional framework was implemented, combining behavioural testing, physiological monitoring, and neuroimaging in healthy older adults.First, we examined how ageing reshapes the relationship between thermoregulation and cognition, showing that circadian-homeostatic alterations co-occur with, but are not reducible to, cognitive decline.We then demonstrated that habitual napping modulates thermoregulatory processes linked to sleep propensity in the healthy older population.Building on this, a one-year nap-suppression intervention revealed that reducing daytime napping in both frequency and duration partially protects episodic and working memory trajectories.Finally, functional MRI results showed that manipulating napping habits alters brain recruitment patterns: nap suppression fosters adaptive compensation, whereas continued habitual napping is associated with inefficient overactivation and dedifferentiation.Altogether, this work provides converging evidence that daytime napping is both a marker and a modifiable determinant of cognitive ageing, as well as circadian dysregulation.By integrating sleep physiology, thermoregulation, and brain correlates, the thesis highlights that behavioural interventions targeting sleepwake consolidation may recalibrate compensatory mechanisms and preserve cognition.These findings underscore the potential of behavioural interventions, centred on sleep-wake regulation, to promote resilience and successful ageing.I am now sitting down behind my desk, 350 pages of thesis manuscript written, more than 450 hours spent in the sleep lab, around 560 hours of scanning in the MRI Room, countless sleepless nights and 95 participants met.However, it is not mainly about these or my results that I am thinking about, but rather everyone that made it all happen and allowed my hard work to be accomplished.I have to start by thanking my dear supervisor, Dr. Christina Schmidt.You have given me the opportunity to pursue a PhD and my goals.We have been through a lot, and our relationship can't be explained.You've been patient, guiding and supportive.You taught me a lot, both in terms of knowledge and scientific rigor, but also in terms of adaptation and creativity.You've never hesitated to push me, even when I thought I was unable.You saw a potential in me and made me work on it.Thank you for everything, for the science, for the laughter, for the great project and the amazing team you built for us to thrive in.This thesis wouldn't have seen the light of day if it weren't also for my co-supervisor, Prof. Philippe Peigneux, who was the one to introduce me to sleep research.Your kindness, goodwill, character and opinions have shaped my thesis journey and myself.I thank you for your availability and having seen my ambitions, my objectives, and put in the work to make them happen.You gently guided me, you directed my efforts without ever taking credit for putting the right ideas in my brain, and most importantly you never fed in my anxiety, but rather soothed it.You were a rock in the storm that is a PhD, without you knowing it.
Language: English
Open Access status: green
OpenAlex ID: W7082420100
Cites: 607
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Related to: 10