Delineating memory reactivation in sleep with verbal and non-verbal retrieval cues.

Sleep supports memory consolidation via the reactivation of newly formed memory traces. One way to investigate memory reactivation in sleep is by exposing the sleeping brain to auditory retrieval cues; a paradigm known as targeted memory reactivation. To what extent the acoustic properties of memory cues influence the effectiveness of targeted memory reactivation, however, has received limited attention. We addressed this question by exploring how verbal and non-verbal memory cues affect oscillatory activity linked to memory reactivation in sleep. Fifty-one healthy male adults learned to associate visual stimuli with spoken words (verbal cues) and environmental sounds (non-verbal cues). Subsets of the verbal and non-verbal memory cues were then replayed during sleep. The voice of the verbal cues was either matched or mismatched to learning. Memory cues (relative to unheard control cues) prompted an increase in theta/alpha and spindle power, which have been heavily implicated in sleep-associated memory processing. Moreover, verbal memory cues were associated with a stronger increase in spindle power than non-verbal memory cues. There were no significant differences between the matched and mismatched verbal cues. Our findings suggest that verbal memory cues may be most effective for triggering memory reactivation in sleep, as indicated by an amplified spindle response.

An Enduring Role for Hippocampal Pattern Completion in Addition to an Emergent Nonhippocampal Contribution to Holistic Episodic Retrieval after a 24†h Delay.

Episodic memory retrieval is associated with the holistic neocortical reinstatement of all event information, an effect driven by hippocampal pattern completion. However, whether holistic reinstatement occurs, and whether hippocampal pattern completion continues to drive reinstatement, after a period of consolidation is unclear. Theories of systems consolidation predict either a time-variant or time-invariant role of the hippocampus in the holistic retrieval of episodic events. Here, we assessed whether episodic events continue to be reinstated holistically and whether hippocampal pattern completion continues to facilitate holistic reinstatement following a period of consolidation. Female and male human participants learned "events" that comprised multiple overlapping pairs of event elements (e.g., person-location, object-location, location-person). Importantly, encoding occurred either immediately before or 24 h before retrieval. Using fMRI during the retrieval of events, we show evidence for holistic reinstatement, as well as a correlation between reinstatement and hippocampal pattern completion, regardless of whether retrieval occurred immediately or 24 h after encoding. Thus, hippocampal pattern completion continues to contribute to holistic reinstatement after a delay. However, our results also revealed that some holistic reinstatement can occur without evidence for a corresponding signature of hippocampal pattern completion after a delay (but not immediately after encoding). We therefore show that hippocampal pattern completion, in addition to a nonhippocampal process, has a role in holistic reinstatement following a period of consolidation. Our results point to a consolidation process where the hippocampus and neocortex may work in an additive, rather than compensatory, manner to support episodic memory retrieval.

A registered report testing the effect of sleep on Deese-Roediger-McDermott false memory: greater lure and veridical recall but fewer intrusions after sleep.

Human memory is known to be supported by sleep. However, less is known about the effect of sleep on false memory, where people incorrectly remember events that never occurred. In the laboratory, false memories are often induced via the Deese-Roediger-McDermott (DRM) paradigm where participants are presented with wordlists comprising semantically related words such as nurse, hospital and sick (studied words). Subsequently, participants are likely to falsely remember that a related lure word such as doctor was presented. Multiple studies have examined whether these false memories are influenced by sleep, with contradictory results. A recent meta-analysis suggests that sleep may increase DRM false memory when short lists are used. We tested this in a registered report (N = 488) with a 2 (Interval: Immediate versus 12 h delay) × 2 (Test Time: 9:00 versus 21:00) between-participant DRM experiment, using short DRM lists (N = 8 words/list) and free recall as the memory test. We found an unexpected time-of-day effect such that completing free recall in the evening led to more intrusions (neither studied nor lure words). Above and beyond this time-of-day effect, the Sleep participants produced fewer intrusions than their Wake counterparts. When this was statistically controlled for, the Sleep participants falsely produced more critical lures. They also correctly recalled more studied words (regardless of intrusions). Exploratory analysis showed that these findings cannot be attributed to differences in output bias, as indexed by the number of total responses. Our overall results cannot be fully captured by existing sleep-specific theories of false memory, but help to define the role of sleep in two more general theories (Fuzzy-Trace and Activation/Monitoring theories) and suggest that sleep may benefit gist abstraction/spreading activation on one hand and memory suppression/source monitoring on the other.

Episodic memory and sleep are involved in the maintenance of context-specific lexical information.

Familiar words come with a wealth of associated knowledge about their variety of usage, accumulated over a lifetime. How do we track and adjust this knowledge as new instances of a word are encountered? A recent study (Cognition) found that, for homonyms (e.g., bank), sleep-associated consolidation facilitates the updating of meaning dominance. Here, we tested the generality of this finding by exposing participants to (Experiment 1; N = 125) nonhomonyms (e.g., bathtub) in sentences that biased their meanings toward a specific interpretation (e.g., bathtub-slip vs. bathtub-relax), and (Experiment 2; N = 128) word-class ambiguous words (e.g., loan) in sentences where the words were used in their dispreferred word class (e.g., "He will loan me money"). Both experiments showed that such sentential experience influenced later interpretation and usage of the words more after a night's sleep than a day awake. We interpret these results as evidence for a general role of episodic memory in language comprehension such that new episodic memories are formed every time a sentence is comprehended, and these memories contribute to lexical processing next time the word is encountered, as well as potentially to the fine-tuning of long-term lexical knowledge. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Do naps benefit novel word learning? Developmental differences and white matter correlates.

Memory representations of newly learned words undergo changes during nocturnal sleep, as evidenced by improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning (at least under the present conditions), and emphasize the need to better understand both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.

Sleep loss disrupts the neural signature of successful learning.

Sleep supports memory consolidation as well as next-day learning. The influential "Active Systems" account of offline consolidation suggests that sleep-associated memory processing paves the way for new learning, but empirical evidence in support of this idea is scarce. Using a within-subjects (n = 30), crossover design, we assessed behavioral and electrophysiological indices of episodic encoding after a night of sleep or total sleep deprivation in healthy adults (aged 18-25 years) and investigated whether behavioral performance was predicted by the overnight consolidation of episodic associations from the previous day. Sleep supported memory consolidation and next-day learning as compared to sleep deprivation. However, the magnitude of this sleep-associated consolidation benefit did not significantly predict the ability to form novel memories after sleep. Interestingly, sleep deprivation prompted a qualitative change in the neural signature of encoding: Whereas 12-20 Hz beta desynchronization-an established marker of successful encoding-was observed after sleep, sleep deprivation disrupted beta desynchrony during successful learning. Taken together, these findings suggest that effective learning depends on sleep but not necessarily on sleep-associated consolidation.

Stronger Associations Between Sleep and Mental Health in Adults with Autism: A UK Biobank Study.

This study examined sleep and its cognitive and affective correlates in adults with and without autism spectrum disorder (ASD), utilizing UK Biobank data. There were no group differences in subjective sleep duration [n = 220 ASD; n = 2200 general population (GP)]. Accelerometer measures of sleep duration or nighttime activity did not differ by group, but sleep efficiency was marginally lower in ASD (n = 83 ASD; n = 824 GP). Sleep efficiency was associated with wellbeing and mental health, and pathways between accelerometer sleep measures and wellbeing and mental health were significantly stronger for adults with ASD (who also reported substantially poorer wellbeing and > 5 × likelihood of experiencing mental distress). These findings highlight the need to monitor sleep to maintain good mental health in adult ASD.

Targeted memory reactivation during sleep can induce forgetting of overlapping memories.

Memory reactivation during sleep can shape new memories into a long-term form. Reactivation of memories can be induced via the delivery of auditory cues during sleep. Although this targeted memory reactivation (TMR) approach can strengthen newly acquired memories, research has tended to focus on single associative memories. It is less clear how TMR affects retention for overlapping associative memories. This is critical, given that repeated retrieval of overlapping associations during wake can lead to forgetting, a phenomenon known as retrieval-induced forgetting (RIF). We asked whether a similar pattern of forgetting occurs when TMR is used to cue reactivation of overlapping pairwise associations during sleep. Participants learned overlapping pairs-learned separately, interleaved with other unrelated pairs. During sleep, we cued a subset of overlapping pairs using TMR. While TMR increased retention for the first encoded pairs, memory decreased for the second encoded pairs. This pattern of retention was only present for pairs not tested prior to sleep. The results suggest that TMR can lead to forgetting, an effect similar to RIF during wake. However, this effect did not extend to memories that had been strengthened via retrieval prior to sleep. We therefore provide evidence for a reactivation-induced forgetting effect during sleep.

Neural Responses to Novel and Existing Words in Children with Autism Spectrum and Developmental Language Disorder.

The formation of new phonological representations is key in establishing items in the mental lexicon. Phonological forms become stable with repetition, time and sleep. Atypicality in the establishment of new word forms is characteristic of children with developmental language disorder (DLD) and autism spectrum disorder (ASD), yet neural changes in response to novel word forms over time have not yet been directly compared in these groups. This study measured habituation of event-related-potentials (ERPs) to novel and known words within and between two sessions spaced 24 hours apart in typically developing (TD) children, and their peers with DLD or ASD. We hypothesised that modulation of the auditory N400 amplitude would mark real-time changes in lexical processing with habituation evident within and across sessions in the TD group, while the DLD group would show attenuated habituation within sessions, and the ASD group attenuated habituation between sessions. Twenty-one typically developing children, 19 children with ASD, and 16 children with DLD listened passively to known and novel words on two consecutive days, while ERPs were recorded using dry electrodes. Counter to our hypotheses, no habituation effect emerged within sessions. However, responses did habituate between sessions, with this effect being reduced in the DLD group, indicating less pre-activation of lexical representations in response to words encountered the previous day. No differences in change over time were observed between the TD and ASD groups. These data are in keeping with theories stressing the importance of sleep-related consolidation in word learning.

Schematic information influences memory and generalisation behaviour for schema-relevant and -irrelevant information.

Schemas modulate memory performance for schema-congruent and -incongruent information. However, it is assumed they do not influence behaviour for information irrelevant to themselves. We assessed memory and generalisation behaviour for information related to an underlying pattern, where a schema could be extracted (schema-relevant), and information that was unrelated and therefore irrelevant to the extracted schema (schema-irrelevant). Using precision measures of long-term memory, where participants learnt associations between words and locations around a circle, we assessed memory and generalisation for schema-relevant and -irrelevant information. Words belonged to two semantic categories: human-made and natural. For one category, word-locations were clustered around one point on the circle (clustered condition), while the other category had word-locations randomly distributed (non-clustered condition). The presence of an underlying pattern in the clustered condition allows for the extraction of a schema that can support both memory and generalisation. At test, participants were presented with old (memory) and new (generalisation) words, requiring them to identify a remembered location or make a best guess. The presence of the clustered pattern modulated memory and generalisation. In the clustered condition, participants placed old and new words in locations consistent with the underlying pattern. In contrast, for the non-clustered condition, participants were less likely to place old and new non-clustered words in locations consistent with the clustered condition. Therefore, we provide evidence that the presence of schematic information modulates memory and generalisation for schema-relevant and -irrelevant information. Our results highlight the need to carefully construct appropriate schema-irrelevant control conditions such that behaviour in these conditions is not modulated by the presence of a schema. Theoretically, models of schema processing need to account for how the presence of schematic information can have consequences for information that is irrelevant to itself.

Word-meaning priming extends beyond homonyms.

When a homonym (e.g., bark) is encountered in a sentential context that biases its interpretation towards a less frequent meaning, subsequent interpretations of the word are more likely to favour that subordinate meaning. Such word-meaning priming effects have been shown to be maintained via sleep-related consolidation, leading some to suggest that declarative memory systems play a crucial role in language comprehension, providing a relatively enduring contextually bound memory trace for the ambiguous word. By this account, word-meaning priming effects should be observable for all words, not just homonyms. In three experiments, participants were exposed to non-homonym targets (e.g., "balloon") in sentences that biased interpretation towards a specific aspect of the word's meaning (e.g., balloon­helium vs. balloon-float). After a ~ 10-30 min delay, the targets were presented in relatedness judgement and associate production tasks to assess whether the sentential contexts enhanced access to the primed aspect of the word's meaning. The results reveal that word-meaning priming effects do extend to non-homonyms. Indeed, there was also some evidence of a more generalised priming that did not rely on prior presentation of the non-homonym itself. We argue that context-specific interpretations of words are maintained during recognition in order to facilitate comprehension over longer periods.

Nap effects on preschool children's learning of letter-sound mappings.

This study explored whether a daytime nap aids children's acquisition of letter-sound knowledge, which is a fundamental component for learning to read. Thirty-two preschool children in Sydney, Australia (Mage  = 4 years;3 months) were taught letter-sound mappings in two sessions: one followed by a nap and the other by a wakeful period. Learning was assessed by explicit letter-sound mappings ("Which sound does this letter make?") and knowledge generalization tasks ("Here's Tav and Cav, which one is /kav/?"). Results from the knowledge generalization task showed better performance after a nap than after wake. However, no nap benefit was found for explicit letter-sound knowledge. This study provides initial evidence that naps could be beneficial for preschool children's learning of letter-sound mappings.

UK children's sleep and anxiety during the COVID-19 pandemic.

BACKGROUND: Sleep and mental wellbeing are intimately linked. This relationship is particularly important to understand as it emerges over childhood. Here we take the opportunity that the COVID-19 pandemic, and resulting lockdown in the UK, presented to study sleep-related behaviour and anxiety in school-aged children. METHODS: Parents and children were asked to complete questionnaires towards the start of the UK lockdown in April-to-May of 2020, then again in August of that year (when many restrictions had been lifted). We explored children's emotional responses to the pandemic and sleep patterns at both time points, from the perspectives of parents and children themselves. RESULTS: Children's bedtime anxiety increased at the start of the lockdown as compared to a typical week; however, by August, bedtime anxiety had ameliorated along with children's COVID-19 related anxiety. Bedtime anxiety predicted how long it took children to fall asleep at night at both the start and the end of the lockdown. Bedtime and wake-up time shifted at the start of lockdown, but interestingly total sleep time was resilient (likely owing to an absence of early school start times) and was not predicted by child anxiety. CONCLUSIONS: These findings further support calls for sleep quality (in particular, time taken to fall asleep) to be taken as a key indicator of mental health in children, particularly under usual circumstances when schools are open and sleep duration may be less resilient.

Does the maturation of early sleep patterns predict language ability at school entry? A Born in Bradford study.

Children's vocabulary ability at school entry is highly variable and predictive of later language and literacy outcomes. Sleep is potentially useful in understanding and explaining that variability, with sleep patterns being predictive of global trajectories of language acquisition. Here, we looked to replicate and extend these findings. Data from 354 children (without English as an additional language) in the Born in Bradford study were analysed, describing the mean intercepts and linear trends in parent-reported day-time and night-time sleep duration over five time points between 6 and 36 months-of-age. The mean difference between night-time and day-time sleep was predictive of receptive vocabulary at age five, with more night-time sleep relative to day-time sleep predicting better language. An exploratory analysis suggested that socioeconomic status was predictive of vocabulary outcomes, with sleep patterns partially mediating this relationship. We suggest that the consolidation of sleep patterns acts as a driver of early language development.

The role of prior lexical knowledge in children's and adults' incidental word learning from illustrated stories.

Children and adults benefit from a new word's phonological neighbors during explicit vocabulary instruction, suggesting that related prior knowledge can support new learning. This study examined the influence of lexical neighborhood structure during incidental word learning-limiting opportunities for strategically engaging prior knowledge-and tested the hypothesis that prior knowledge would provide additional support during subsequent consolidation. Children aged 8-10 years (Experiment 1) and adults (Experiment 2) were presented with 15 pseudowords embedded in a spoken story with illustrations, and were then tested on their recognition and recall of the new word-forms immediately, the next day, and one week later. The pseudowords had either no, one, or many English phonological neighbors, varying the potential connections to existing knowledge. After encountering the pseudowords in this incidental training paradigm, neither children nor adults benefited from phonological neighbors in recall, and children were better at recognizing items without neighbors. The neighbor influence did not change with opportunities for consolidation in either experiment, nor did it relate to learners' existing vocabulary ability. Exploratory analyses revealed that children experienced bigger benefits from offline consolidation overall, with adults outperforming children only for many-neighbor items one week after exposure. We discuss how the neighbor benefit in word learning may be constrained by learning context, and how the enhanced benefits of offline consolidation in childhood extend to vocabulary learning in more naturalistic contexts. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Timing storytime to maximize children's ability to retain new vocabulary.

Shared storybook reading is a key aid to vocabulary acquisition during childhood. However, word learning research has tended to use unnaturalistic (explicit) training regimes. Using a storybook paradigm, we examined whether children (particularly those with weaker vocabularies) are more likely to retain new words if they learn them closer to sleep. Parents read their children (5- to 7-year-olds; N = 237) an alien adventure story that contained 12 novel words with illustrations at one of two training times: at bedtime or 3-5 h before bedtime. Using online tasks, parents tested their children's ability to recall the new words (production) and associate them with pictures (comprehension) immediately after hearing the story and again the following morning. As hypothesized, we replicated two findings. First, children showed overnight improvements in their ability to produce and comprehend new words when tested again the next day. Second, children with better existing vocabulary knowledge showed larger overnight gains in new word comprehension. Counter to expectations, overnight gains in comprehension were larger if the story was read 3-5 h before bedtime rather than at bedtime. These ecologically valid findings are consistent with theories that characterize word learning as a prolonged process supported by mechanisms such as consolidation and retrieval practice, with existing vocabulary knowledge acting as an important source of variability in retention. The findings provide preliminary evidence that encountering new words in stories later in the day (but not too close to sleep) may help to harness vocabulary growth and may be more beneficial than leaving shared storybook reading just for bedtime.

Sleep-dependent consolidation in children with comprehension and vocabulary weaknesses: it'll be alright on the night?

BACKGROUND: Vocabulary is crucial for an array of life outcomes and is frequently impaired in developmental disorders. Notably, 'poor comprehenders' (children with reading comprehension deficits but intact word reading) often have vocabulary deficits, but underlying mechanisms remain unclear. Prior research suggests intact encoding but difficulties consolidating new word knowledge. We test the hypothesis that poor comprehenders' sleep-associated vocabulary consolidation is compromised by their impoverished lexical-semantic knowledge. METHODS: Memory for new words was tracked across wake and sleep to assess encoding and consolidation in 8-to-12-year-old good and poor comprehenders. Each child participated in two sets of sessions, one beginning in the morning (AM-encoding) and the other in the evening (PM-encoding). In each case, they were taught 12 words and were trained on a spatial memory task. Memory was assessed immediately, 12- and 24-hr later via stem-completion, picture-naming, and definition tasks to probe different aspects of word knowledge. Long-term retention was assessed 1-2 months later. RESULTS: Recall of word-forms improved over sleep and postsleep wake, as measured in both stem-completion and picture-naming tasks. Counter to hypotheses, deficits for poor comprehenders were not observed in consolidation but instead were seen across measures and throughout testing, suggesting a deficit from encoding. Variability in vocabulary knowledge across the whole sample predicted sleep-associated consolidation, but only when words were learned early in the day and not when sleep followed soon after learning. CONCLUSIONS: Poor comprehenders showed weaker memory for new words than good comprehenders, but sleep-associated consolidation benefits were comparable between groups. Sleeping soon after learning had long-lasting benefits for memory and may be especially beneficial for children with weaker vocabulary. These results provide new insights into the breadth of poor comprehenders' vocabulary weaknesses, and ways in which learning might be better timed to remediate vocabulary difficulties.

Growing up with interfering neighbours: the influence of time of learning and vocabulary knowledge on written word learning in children.

Evidence suggests that new vocabulary undergoes a period of strengthening and integration offline, particularly during sleep. Practical questions remain, however, including whether learning closer to bedtime can optimize consolidation, and whether such an effect varies with vocabulary ability. To examine this, children aged 8-12-years-old (n 59) were trained on written novel forms (e.g. BANARA) in either the morning (long delay) or the evening (short delay). Immediately after training and the next day, lexical competition (a marker of integration) was assessed via speeded semantic decisions to neighbouring existing words (e.g. BANANA); explicit memory was measured via recognition and recall tasks. There were no main effects indicating performance changes across sleep for any task, counter to studies of spoken word learning. However, a significant interaction was found, such that children with poorer vocabulary showed stronger lexical competition on the day after learning if there was a short delay between learning and sleep. Furthermore, while poorer vocabulary was associated with slower novel word recognition speed before and after sleep for the long delay group, this association was only present before sleep for the short delay group. Thus, weak vocabulary knowledge compromises novel word acquisition, and when there is a longer period of post-learning wake, this disadvantage remains after a consolidation opportunity. However, when sleep occurs soon after learning, consolidation processes can compensate for weaker encoding and permit lexical integration. These data provide preliminary suggestion that children with poorer vocabulary may benefit from learning new words closer to bedtime.

United we fall: All-or-none forgetting of complex episodic events.

Do complex event representations fragment over time, or are they instead forgotten in an all-or-none manner? For example, if we met a friend in a café and they gave us a present, do we forget the constituent elements of this event (location, person, and object) independently, or would the whole event be forgotten? Research suggests that item-based memories are forgotten in a fragmented manner. However, we do not know how more complex episodic, event-based memories are forgotten. We assessed both retrieval accuracy and dependency-the statistical association between the retrieval successes of different elements from the same event-for complex events. Across 4 experiments, we show that retrieval dependency is found both immediately after learning and following a 12-hr and 1-week delay. Further, the amount of retrieval dependency after a delay is greater than that predicted by a model of independent forgetting. This dependency was only seen for coherent "closed-loops," where all pairwise associations between locations, people, and objects were encoded. When "open-loops" were learned, where only 2 out of the 3 possible associations were encoded, no dependency was seen immediately after learning or after a delay. Finally, we also provide evidence for higher retention rates for closed-loops than for open-loops. Therefore, closed-loops do not fragment as a function of forgetting and are retained for longer than are open-loops. Our findings suggest that coherent episodic events are not only retrieved, but also forgotten, in an all-or-none manner. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Investigating the formation and consolidation of incidentally learned trust.

People make inferences about the trustworthiness of others based on their observed gaze behavior. Faces that consistently look toward a target location are rated as more trustworthy than those that look away from the target. Representations of trust are important for future interactions; yet little is known about how they are consolidated in long-term memory. Sleep facilitates memory consolidation for incidentally learned information and may therefore support the retention of trust representations. We investigated the consolidation of trust inferences across periods of sleep or wakefulness. In addition, we employed a memory cueing procedure (targeted memory reactivation [TMR]) in a bid to strengthen certain trust memories over others. We observed no difference in the retention of trust inferences following delays of sleep or wakefulness, and there was no effect of TMR in either condition. Interestingly, trust inferences remained stable 1 week after learning, irrespective of the initial postlearning delay. A second experiment showed that this implicit learning occurs despite participants' being unable to explicitly recall the gaze behavior of specific faces immediately after encoding. Together, these results suggest that gist-like, social inferences are formed at the time of learning without retaining the original episodic memory and thus do not benefit from offline consolidation through replay. We discuss our findings in the context of a novel framework whereby trust judgments reflect an efficient, powerful, and adaptable storage device for social information. (PsycInfo Database Record (c) 2020 APA, all rights reserved).