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Abstract :
[en] Introduction. Aging is associated with alterations in sleep-wake regulation that have been associated with changes in brain structural integrity. In particular, the ability to generate slow oscillations during non-rapid eye movement (NREM) sleep decreases as early as in the 5th decade of life, predominantly over frontal regions. While previous investigations have identified macrostructural brain correlates of the age-related decrement in sleep slow waves generation, their relationships with brain tissue microstructure remain poorly understood.
Methods. We recorded sleep under electroencephalography in 99 healthy older individuals (mean age = 59.6 ± 5.2 years; 66 women), and we quantified slow waves generation using the overnight cumulated power density in the delta band (0.5-4 Hz) during NREM sleep over the frontal Fz derivation. All participants also underwent 3T magnetic resonance imaging (MRI) scans to investigate tissue myelin content based on quantitative magnetization transfer (MT) saturation mapping, as well as diffusion-based metrics derived from neurite orientation dispersion and density imaging (NODDI) model. A region of interest covering bilateral medial prefrontal cortices was used to extract regional grey matter values.
Results. We first observed that MT signal in the medial prefrontal cortex was positively associated with higher neurite orientation dispersion (r = .30, p = .003) and density (r = .22, p = .03), supposedly reflecting preserved microstructural integrity. Crucially, overnight NREM sleep slow waves generation was significantly related to higher prefrontal MT signal (r = .22, p = .03), but not to NODDI metrics (dispersion: r = .02, p = .85; density: r = .09, p = .36). Generalized linear mixed models adjusted for demographics and total sleep time confirmed these relationships, although as a statistical trend for MT signal (F1,93 = 3.64, p = .06).
Discussion. Our findings suggest a positive association between tissue myelin content within medial prefrontal grey matter and generation of slow waves during NREM sleep in aging. Preserved prefrontal myelination may facilitate neuronal synchronization through enhanced cortico-cortical connections, resulting in higher power density in the slower frequency band. Given the existing link between sleep characteristics and age-related cognitive decline, these results may have implications for successful cognitive aging.
Support: FNRS, ULiège, ARC17/21-09, FEDER, WBI, Clerdent Foundation, Leon Frédéricq Foundation
