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SUMMARYPrevious studies suggest that sleep-specific brain activity patterns such as sleep spindles and electroencephalographic slow-wave activity contribute to the consolidation of novel memories. The generation of both sleep spindles and slow-wave activity relies on synchronized oscillations in a thalamo-cortical network that might be implicated in synaptic strengthening (spindles) and downscaling (slow-wave activity) during sleep. This study further examined the association between electroencephalographic power during non-rapid eye movement sleep in the spindle (sigma, 12-16 Hz) and slow-wave frequency range (0.1-3.5 Hz) and overnight memory consolidation in 20 healthy subjects (10 men, 27.1 ± 4.6 years). We found that both electroencephalographic sigma power and slow-wave activity were positively correlated with the pre-post-sleep consolidation of declarative (word list) and procedural (mirror-tracing) memories. These results, although only correlative in nature, are consistent with the view that processes of synaptic strengthening (sleep spindles) and synaptic downscaling (slow-wave activity) might act in concert to promote synaptic plasticity and the consolidation of both declarative and procedural memories during sleep. IN TROD UCTI ONEvidence from molecular to behavioural studies indicates that sleep fosters learning, memory and underlying neural plasticity (Diekelmann and Born, 2010). However, the contribution of the predominant sleep stages, rapid eye movement (REM) and non-REM (NREM) sleep, and of associated neural processes to the consolidation of newly encoded memories in the major memory systems, declarative and non-declarative memory, remains to be further elucidated.Recent findings suggest that sleep spindles, brief but powerful bursts of synchronous neuronal firing during mammalian stage 2 sleep in the electroencephalogram (EEG) sigma range (12-16 Hz), and EEG slow-wave activity (SWA), highly-synchronized oscillations during NREM sleep (0.1-3.5 Hz), might represent oscillatory activity that promotes sleep-related synaptic plasticity (Rosanova and Ulrich, 2005;Tononi and Cirelli, 2006). Animal studies indicate that sleep spindles might foster intracellular Ca 2+ -dependent mechanisms leading to the consolidation of new memories through synaptic strengthening (Steriade, 2003). In contrast, SWA and underlying Ôdown-statesÕ of extensive hyperpolarization and neuronal silencing and subsequent Ôup-statesÕ of depolarization and intense neuronal firing (Steriade, 2006) might sharpen the information-to-noise ratio and novel memory representations through synaptic downscaling (Tononi and Cirelli, 2006).Earlier work proposed that NREM sleep might preferentially promote declarative memory, whereas REM sleep might predominantly facilitate non-declarative learning (Plihal and Born, 1997). Consistently, NREM sleep-related sleep spindle density has been shown to be enhanced during nocturnal sleep following training on a declarative word-pair association task (Gais et al., 2002). Additionally, the increase in sle...

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Initially independent lines of research suggest that sleep‐specific brain activity patterns, observed as electroencephalographic slow oscillatory and sleep spindle activity, promote memory consolidation and underlying synaptic refinements. Here, we further tested the emerging concept that specifically the coordinated interplay of slow oscillations and spindle activity (phase‐amplitude coupling) support memory consolidation. Particularly, we associated indices of the interplay between slow oscillatory (0.16–1.25 Hz) and spindle activity (12–16 Hz) during non‐rapid eye movement sleep (strength [modulation index] and phase degree of coupling) in 20 healthy adults with parameters of overnight declarative (word‐list task) and procedural (mirror‐tracing task) memory consolidation. The pattern of results supports the notion that the interplay between oscillations facilitates memory consolidation. The coincidence of the spindle amplitude maximum with the up‐state of the slow oscillation (phase degree) was significantly associated with declarative memory consolidation (r = .65, p = .013), whereas the overall strength of coupling (modulation index) correlated with procedural memory consolidation (r = .45, p = .04). Future studies are needed to test for potential causal effects of the observed association between neural oscillations during sleep and memory consolidation, and to elucidate ways of modulating these processes, for instance through non‐invasive brain‐stimulation techniques.