Electrophysiological mechanisms of memory consolidation in human non-rapid eye movement sleep

Purpose of the review: Pioneering work in rodents has shown that the reactivation of recently acquired memories during sleep is a key mechanism underlying the beneficial effect of sleep on memory consolidation. In this review, we consider recent evidence of memory reactivation processes in human sleep. Recent findings: The precise temporal coupling of sleep spindles to slow oscillations during non-rapid eye movement sleep plays a central role in sleep-associated memory consolidation. Both correlational studies and studies directly manipulating oscillatory activity in the sleeping brain have confirmed that spindles coupled to slow oscillations are better predictors of memory than uncoupled spindles, and that the greatest memory benefit comes when spindles are tightly coupled to the up-state of the slow oscillation. Recent evidence suggests that memory content is reactivated during sleep, with a functional benefit for memory performance after sleep. Reactivation events are time-locked around slow oscillation-spindle coupling events, as well as sharp-wave ripples in hippocampus. Summary: Memory reactivation, which is facilitated by slow oscillation-spindle coupling events, can be observed during human sleep and shows promise as a prime mechanism underlying sleep’s beneficial effects on memory.