Study objectives: Sleep deprivation and daytime somnolence impair numerous aspects of physical, cognitive, and memory performance. However, most studies examining the effect of somnolence on brain function focus on acute sleep restriction in young adults. We examine the relationship between chronic daytime somnolence and connectivity in six brain networks in both young and elderly subjects using stimulus-free resting-state functional magnetic resonance imaging.
Design: Cross-sectional.
Setting: Outpatient research at the Massachusetts General Hospital.
Participants: Young (n = 27) and elderly (n = 84) healthy, cognitively normal volunteers.
Interventions: None.
Measurements and results: Compared with young subjects, cognitively normal elderly adults report less daytime somnolence on the Epworth Sleepiness Scale (ESS) (P = 0.019) and display reduced default mode network (DMN) connectivity (P = 0.004). Across all subjects, increasing daytime sleepiness was associated with decreasing functional connectivity in the DMN (P = 0.003, partial r of ESS = -0.29). There was no difference in the slope of this relationship between young adults and elderly subjects. No other cortical networks were correlated with daytime sleepiness. Daytime sleepiness and DMN connectivity were not related to sex, brain structure, or body mass index.
Conclusions: These findings suggest that daytime sleepiness is associated with impaired connectivity of the DMN in a manner that is distinct from the effects of aging. This association is important to consider in any study using DMN connectivity as a biomarker. Additionally, these results may help identify those subjects at risk for future memory decline.
Keywords: Epworth Sleepiness Scale; functional connectivity; magnetic resonance imaging; neuroimaging; sleep.