Abstract
Even though sleep modification is a hallmark of the aging process, age-related changes in functional connectivity using functional Magnetic Resonance Imaging (fMRI) during sleep, remain unknown. Here, we combined electroencephalography and fMRI to examine functional connectivity differences between wakefulness and light sleep stages (N1 and N2 stages) in 16 young (23.1 ± 3.3y; 7 women), and 14 older individuals (59.6 ± 5.7y; 8 women). Results revealed extended, distributed (inter-between) and local (intra-within) decreases in network connectivity during sleep both in young and older individuals. However, compared to the young participants, older individuals showed lower decreases in connectivity or even increases in connectivity between thalamus/basal ganglia and several cerebral regions as well as between frontal regions of various networks. These findings reflect a reduced ability of the older brain to disconnect during sleep that may impede optimal disengagement for loss of responsiveness, enhanced lighter and fragmented sleep, and contribute to age effects on sleep-dependent brain plasticity.
Highlights
Between regions of sensorimotor and central executive networks that would support the fading of sensory awareness and the disengagement of executive control during sleep
The age-related decreases in deep sleep, slow waves and sleep spindles, may reflect a reduced ability to recruit and synchronize local cortical generators of sleep rhythms which drive the crosstalk between cortical areas and favor local over distant connectivity
We concomitantly recorded the sleep of young and older individuals with EEG and functional magnetic resonance imaging (fMRI) to investigate the changes in functional connectivity that occur during sleep in healthy aging
Summary
Between regions of sensorimotor and central executive networks that would support the fading of sensory awareness and the disengagement of executive control during sleep. As compared to younger individuals, older participants show fewer slow waves, fewer sleep spindles[15,18] and a reduced amount of deep sleep (N3)[17,19]. We hypothesized that older participants would show a lower breakdown of functional connectivity during NREM sleep as compared to younger ones. In line with this assumption, our results demonstrated that young and older individuals present similar reductions in functional connectivity when N2 is compared to wakefulness or N1, older individuals presented significant lower decreases and even increases in distributed (inter-between networks) and local (intra-within network) functional connectivity
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