Larger capacity for unconscious versus conscious episodic memory Highlights d Humans draw inferences when encoding episodes with and without consciousness d Memory capacity is larger for unconscious than conscious episodic memory d Hippocampus supports encoding and retrieval with and without consciousness d Conscious versus unconscious encoding/retrieval recruits additional brain regions

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We are unresponsive during slow-wave sleep but continue monitoring external events for survival. Our brain wakens us when danger is imminent. If events are non-threatening, our brain might store them for later consideration to improve decision-making. To test this hypothesis, we examined whether simultaneously sleep-played foreign words and translation words are encoded/stored and which neural-electrical events facilitate encoding/storage. A closed-loop algorithm targeted word pairs to slow-wave peaks or troughs. Retrieval tests were given 12 and 36 hours later. These tests required decisions regarding the semantic category of previously sleep-played foreign words. The sleep-played vocabulary influenced awake decision-making 36 hours later, if targeted to troughs. The words' linguistic processing raised neural complexity. The words' semantic-associative encoding was supported by increased theta power during the ensuing peak. Fast-spindle power ramped up during a second peak likely aiding consolidation. Hence, new vocabulary played during slow-wave sleep was stored and influenced decision-making days later.

Sleep improves memory consolidation, including hippocampus-dependent declarative memory. It is thought that by associating multiple aspects of an experience, the hippocampus enables its transformation into an enduring memory. Most research on human sleep and declarative memory uses exhaustive learning of word-pair associations. Here we present the visual paired association learning (vPAL) paradigm, in which participants learn new associations between images of celebrities and animals. vPAL associations are based on a one-shot exposure that resembles learning in natural conditions. Furthermore, vPAL is an engaging short paradigm that does not require rehearsal or reading, making it valuable for clinical settings. We tested if vPAL can reveal a role for sleep in memory consolidation by assessing the specificity of memory recognition, and the cued recall performance, before and after sleep. We found that a daytime nap improved the stability of recognition memory (decay was minimized) compared to identical intervals of wakefulness. By contrast, cued recall of associations did not exhibit significant sleep-dependent effects. Investigating memory consolidation during sleep with the vPAL paradigm opens up new avenues for future research across ages and heterogeneous populations in health and disease.

Slow-wave sleep (SWS) is a fundamental physiological process, and its modulation is of interest for basic science and clinical applications. However, automatised protocols for the suppression of SWS are lacking. We describe the development of a novel protocol for the automated detection (based on the whole head topography of frontal slow waves) and suppression of SWS (through closed-loop modulated randomised pulsed noise), and assessed the feasibility, efficacy and functional relevance compared to sham stimulation in 15 healthy young adults in a repeated-measure sleep laboratory study.Auditory compared to sham stimulation resulted in a highly significant reduction of SWS by 30% without affecting total sleep time. The reduction of SWS was associated with an increase in lighter non-rapid eye movement sleep and a shift of slow-wave activity towards the end of the night, indicative of a homeostatic response and functional relevance. Still, cumulative slow-wave activity across the night was significantly