Integrating Astrocytes in the Sleep-Wake Cycle: The Time Is Now.

Astrocytes are emerging as critical regulators of the sleep-wake cycle, actively contributing to both sleep homeostasis and circadian rheostasis. This dual role challenges neuron-centric frameworks that have dominated sleep and circadian biology and highlights astrocytes as potential integrators of internal temporal information. Experimental evidence shows that astrocytic calcium dynamics correlate with sleep state and that manipulating astrocytes can alter sleep architecture and homeostasis. In parallel, key aspects of circadian timekeeping can be autonomously driven by astrocytic clocks, with pulses of rhythmic GABA and glutamate able to synchronize circadian circuits and support circadian patterns of behavior. These findings are coherent with the idea that astrocytes can act as context-dependent integrators to convey environmental cues and internal states to neuronal circuitries and promote adaptive behavior. Incorporating astrocytes into conceptual models of the sleep-wake cycle may help reconcile contradictory findings and offer new frameworks to better understand how salient internal temporal representations are encoded within the brain.