Memory performance is positively affected by sleep. A wealth of studies have described how sleep, or certain aspects thereof, assist in the stabilisation of previously learnt information. Roy Cox describes a number of studies investigating the relation between sleep and memory from a cognitive neuroscience perspective. More specifically, he explores the mechanisms underlying the reactivation and consolidation of declarative, mostly episodic, memory traces in humans. Cox’s main focus is on brain rhythms during non-rapid eye movement sleep (NREM), and whether they could support systems-level consolidation.