Sleep-dependent memory consolidation is related to perceived value of learned material

Although many types of newly encoded information can be consolidated during sleep, an enhanced effect has been found for memories tagged as relevant to the future, such as through knowledge of future testing or payment for successful recall. In the current study, participants (n = 80) learned Welsh and Breton translations of English words, and intrinsic relevance of learned material was operationalized as perceived value of the Welsh and Breton languages. Participants were non-Welsh native English speakers who had recently arrived in Wales. Memory for the words was tested immediately and 12 h later, after either a period of wake or a period of sleep. An increase in recall for both languages was found after sleep, but not after wake. Importantly, for the sleep condition, overnight improvement in Welsh word recall was associated with participants’ level of valuing the Welsh language. This association was not found for the wake period condition. These findings support previous indications of an active role of sleep in the consolidation of memories relevant for the future, and demonstrate that this effect may be modulated by individual differences in perceived value of the learned material. It remains to be established whether this association is mediated by an emotional attachment to the language or a cognitive facility with it, or both

Overnight consolidation aids the transfer of statistical knowledge from the medial temporal lobe to the striatum

Sleep is important for abstraction of the underlying principles (or gist) which bind together conceptually related stimuli, but little is known about the neural correlates of this process. Here, we investigate this issue using overnight sleep monitoring and functional magnetic resonance imaging (fMRI). Participants were exposed to a statistically structured sequence of auditory tones then tested immediately for recognition of short sequences which conformed to the learned statistical pattern. Subsequently, after consolidation over either 30min or 24h, they performed a delayed test session in which brain activity was monitored with fMRI. Behaviorally, there was greater improvement across 24h than across 30min, and this was predicted by the amount of slow wave sleep (SWS) obtained. Functionally, we observed weaker parahippocampal responses and stronger striatal responses after sleep. Like the behavioral result, these differences in functional response were predicted by the amount of SWS obtained. Furthermore, connectivity between striatum and parahippocampus was weaker after sleep, whereas connectivity between putamen and planum temporale was stronger. Taken together, these findings suggest that abstraction is associated with a gradual shift from the hippocampal to the striatal memory system and that this may be mediated by SWS

Sleep spindles provide indirect support to the consolidation of emotional encoding contexts

Emotional memories tend to be strengthened ahead of neutral memories during sleep-dependent consolidation. In recent work, however, we found that this is not the case when emotion pertains to the contextual features of a memory instead of its central constructs, suggesting that emotional contexts are influenced by distinct properties of sleep. We therefore examined the sleep-specific mechanisms supporting representations of emotional context and asked whether these differ to those already implicated in central emotional memory processing, such as rapid eye movement sleep (REM). Participants encoded neutral foreground images that were each associated with an emotionally negative or neutral background (context) image. Immediate and delayed tests for the emotionality of the foreground/background image association were separated by a 4-h consolidation period, which consisted of either total wakefulness or included a 2-h polysomnographically monitored nap. Although memory for negative contexts was not associated with REM, or any other parameter of sleep, sleep spindles (12–15 Hz) predicted increased forgetting and slowed response times for neutral contexts. Together with prior work linking spindles to emotional memory processing, our data may suggest that spindles provide multi-layered support to emotionally salient memories in sleep, with the nature of such effects depending on whether the emotionality of these memories pertains to their central or contextual features. Therefore, whereas spindles may mediate a direct strengthening of central emotional information, as suggested in prior work, they may also provide concurrent indirect support to emotional contexts by working to suppress non-salient neutral contexts

Consolidation of vocabulary is associated with sleep in children

Although the acquisition of a novel word is apparently rapid, adult research suggests that integration of novel and existing knowledge (measured by engagement in lexical competition) requires sleep-associated consolidation. We present the first investigation of whether a similar time-course dissociation characterizes word learning across development. Consistent with previous research but counter to adults, 712-year-olds showed sleep-associated consolidation effects in declarative but not procedural memory. Nevertheless, the relationship between sleep and word learning in children was remarkably similar to the pattern for adults. Following exposure to nonword competitors (e.g. biscal) in the a.m. or p.m., childrens ability to recognize and recall the nonwords improved only after sleep (after approximately 12-hrs for the p.m. group and 24-hrs for the a.m. group), with performance stable 1 week later. Novel nonwords only induced lexical competition effects after sleep. These findings suggest that children utilize a dual memory system when acquiring and integrating new vocabulary and highlight sleep as integral to this process. A video abstract of this article can be viewed at http://www.youtube.com/watch?feature=youtube_gdata&v=2UNuKCAakOk&gl=GB