Wake consolidates event memory, sleep binds it with context

Sleep is thought to be superior to wakefulness in consolidating memory, due to a hippocampus-driven process enhancing the contextual integration of events. We compared recall of associative memory in different contexts, and found that memory is also consolidated during wakefulness, although in a qualitatively distinct way. Healthy participants performed a cued stimulus-response (S-R) learning task requiring speeded object classification. Learning was followed by 2 hours of sleep or wakefulness. Reaction times revealed stronger S-R memory after sleep than wakefulness with retrieval in the same context, and this benefit was linked to increased sleep spindle activity. In contrast, S-R memory was stronger after wakefulness than sleep when tested in a different context. This wake-dependent enhancement had a fast onset and was reversed by delayed sleep. We conclude that, unlike sleep strengthening the binding of an event with its context, wakefulness stabilizes event representations itself, i.e., not bound to a specific context.