Young and old adult brains experience opposite effects of acute sleep restriction on the functional connectivity network.

Chronic, long-term sleep loss is detrimental to brain health and cognitive ability. However, older adults are affected differently by acute, short-term loss of sleep than young and middle-aged adults. Older adults are more resilient to the effects of acute sleep loss and, depending on the cognitive domain, may be completely unaffected while younger adults suffer. To elucidate the brain network responses to sleep loss underlying these cognitive differences between age groups, we investigated the static and dynamic functional connectivity effects of acute sleep restriction (sleep limited to 3 hours) and how these effects differ between younger adults (20-30 years) and older adults (65-75 years). We found a functional connectivity subnetwork that was primarily strengthened in younger adults after acute sleep restriction but weakened in older adults after acute sleep restriction. Similar crossover interactions were consistently observed in further analyses of functional connectivity degree, modularity, and dynamic functional connectivity state fractional occupancy. Our findings demonstrate that the effect of acute sleep restriction on older adults is fundamentally different from that on younger adults. These results most strongly support the compensation theory of ageing, which predicts a fundamental shift in the effects of acute sleep loss, rather than a mere dampening of the sleep benefits experienced by younger adults.