Sleep deprivation reduces functional connectivity within the brain's Default Mode Network and weakens its anti-correlation with the task-positive network. These effects occur both at rest and during a visual attention task, indicating a robust alteration in intrinsic brain network organization. The study involved 26 healthy participants scanned after a normal night of sleep and after about 24 hours of total sleep deprivation.
In healthy older adults, functional connectivity within brain networks (executive control and default mode networks) declines over four years, indicating a loss of functional specialization with aging. Between these networks, connectivity initially increases (greater segregation) but later decreases, following a u-shaped trajectory. The rate of this later loss in segregation is linked to a decline in processing speed. These brain connectivity changes are independent of gray matter volume loss. The findings connect age-related changes in brain network function to age-related cognitive decline.
When people are sleep-deprived, spontaneous eye closures that signal the onset of sleep become more frequent. Using task-free fMRI in sleep-deprived participants, the study found that these eye closures are accompanied by widespread co-activation of sensory cortices (visual, auditory, somatosensory) and the default mode network, consistent with internal sensory activity without external input. Co-activation of fronto-parietal attentional areas may reflect resistance to sleep or engagement of mental imagery. These brain activity patterns differed from those during cued eye closures in rested participants and from mind-wandering or light sleep. Eye closures also reduced functional connectivity within the default mode and dorsal attention networks, adding to reductions already caused by sleep deprivation. Thalamic deactivation occurred during eye closures in the sleep-deprived state but similar changes appeared when well-rested.