Sound asleep, yet still listening: auditory processing during human sleep.

Sleepers can wake to their name, but ignore louder irrelevant sounds, a paradox that suggests more than simple sensory gating. Growing evidence reveals flexible auditory coupling during human sleep, ranging from complete disconnection to high-level cognitive processing and even to physical responses. Here, we synthesize the multiple cognitive levels at which auditory stimuli are processed (or not) during human sleep and outline factors modulating this processing. Moments of sensory isolation may promote restoration and memory consolidation, while moments of environmental coupling enable threat detection. We speculate that no single optimal balance exists; rather, the ideal degree of sensory coupling shifts with individuals and contexts. Chronic dysregulation of this balance may contribute to the clinical picture of sleep disorders, including insomnia and hypersomnia.