Sleep-related Consolidation Research Articles

Altered functional connectivity in the hippocampal and striatal systems after motor sequence learning consolidation in medial temporal lobe epilepsy individuals.

Both the hippocampal and striatal systems participate in motor sequence learning (MSL) in healthy subjects, and the prominent role of the hippocampal system in sleep-related consolidation has been demonstrated. However, some pathological states may change the functional dominance between these two systems in MSL consolidation. To better understand the functional performance within these two systems under the pathological condition of hippocampal impairment, we compared the functional differences after consolidation between patients with left medial temporal lobe epilepsy (LmTLE) and healthy control subjects (HCs). We assessed participants' performance on the finger-tapping task (FTT) during acquisition (on day 1) and after consolidation during sleep (on day 2). All participants underwent an MRI scan (T1 and resting state) before each FTT. We found that the LmTLE group showed performance deficits in offline consolidation compared to the HC group. The LmTLE group exhibited structural changes, such as decreased gray matter volume (GMV) in the left hippocampus and increased GMV in the right putamen (striatum). Our results also revealed that whereas the main effect of consolidation was observed in the hippocampus-related functional connection in the HC group, it was only evident in the striatum-related functional loop in the LmTLE group. Our findings indicated that LmTLE patients may rely more on the striatal system for offline consolidation because of structural impairments in the hippocampus. Additionally, this compensatory mechanism may not fully substitute for the role of the impaired hippocampus itself.NEW & NOTEWORTHY Motor sequence learning (MSL) relies on both the hippocampal and striatal systems, but whether functional performance is altered after MSL consolidation when the hippocampus is impaired remains unknown. Our results indicated that whereas the main effect of consolidation was observed in the hippocampus-related functional connection in the healthy control (HC) group, it was only evident in the striatum-related functional loop in the left medial temporal lobe epilepsy (LmTLE) group.

Microstructural dynamics of motor learning and sleep-dependent consolidation: A diffusion imaging study

Memory consolidation can benefit from post-learning sleep, eventually leading to long-term microstructural brain modifications to accommodate new memory representations. Non-invasive diffusion-weighted magnetic resonance imaging (DWI) allows the observation of (micro)structural brain remodeling after time-limited motor learning. Here, we combine conventional diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) that allows modeling dendritic and axonal complexity in gray matter to investigate with improved specificity the microstructural brain mechanisms underlying time- and sleep-dependent motor memory consolidation dynamics. Sixty-one young healthy adults underwent four DWI sessions, two sequential motor trainings, and a night of total sleep deprivation or regular sleep distributed over five days. We observed rapid-motor-learning-related remodeling in occipitoparietal, temporal, and motor-related subcortical regions, reflecting temporary dynamics in learning-related neuronal brain plasticity processes. Sleep-related consolidation seems not to exert a detectable impact on diffusion parameters, at least on the timescale of a few days.

Does Motor Memory Reactivation through Practice and Post-Learning Sleep Modulate Consolidation?

Retrieving previously stored information makes memory traces labile again and can trigger restabilization in a strengthened or weakened form depending on the reactivation condition. Available evidence for long-term performance changes upon reactivation of motor memories and the effect of post-learning sleep on their consolidation remains scarce, and so does the data on the ways in which subsequent reactivation of motor memories interacts with sleep-related consolidation. Eighty young volunteers learned (Day 1) a 12-element Serial Reaction Time Task (SRTT) before a post-training Regular Sleep (RS) or Sleep Deprivation (SD) night, either followed (Day 2) by morning motor reactivation through a short SRTT testing or no motor activity. Consolidation was assessed after three recovery nights (Day 5). A 2 × 2 ANOVA carried on proportional offline gains did not evidence significant Reactivation (Morning Reactivation/No Morning Reactivation; p = 0.098), post-training Sleep (RS/SD; p = 0.301) or Sleep*Reactivation interaction (p = 0.257) effect. Our results are in line with prior studies suggesting a lack of supplementary performance gains upon reactivation, and other studies that failed to disclose post-learning sleep-related effects on performance improvement. However, lack of overt behavioural effects does not detract from the possibility of sleep- or reconsolidation-related covert neurophysiological changes underlying similar behavioural performance levels.

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., balloon‑helium 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.

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.

Improving online and offline gain from repetitive practice using anodal tDCS at dorsal premotor cortex

Administering anodal transcranial direct current stimulation at the left dorsal premotor cortex (PMd) but not right PMd throughout the repetitive practice of three novel motor sequences resulted in improved offline performance usually only observed after interleaved practice. This gain only emerged following overnight sleep. These data are consistent with the proposed proprietary role of left PMd for motor sequence learning and the more recent claim that PMd is central to sleep-related consolidation of novel skill memory.

Dysfunctional Overnight Memory Consolidation in Patients with Schizophrenia in Comparison to Healthy Controls: Disturbed Slow-Wave Sleep as Contributing Factor?

Introduction: Memory deficiency has been shown in schizophrenia patients, but results on the role of sleep parameters in overnight consolidation of associative verbal memory are still missing. Therefore, the aim of our study was to elucidate underlying processes of impaired sleep-related consolidation of associative word pairs in schizophrenia including standard sleep parameters as well as sleep spindle counts and spectral analysis. Methods: Eighteen stably medicated schizophrenia patients and 24 healthy age-matched controls performed an associative declarative memory task before and after polysomnographic recordings. Part of the participants expected verbal associative memory testing in the morning, while the others did not. Furthermore, participants filled in self-rating questionnaires of schizophrenia-typical experiences (Eppendorf Schizophrenia Inventory [ESI] and Psychotic Symptom Rating Scale). Results: Schizophrenia patients performed worse in verbal declarative memory in the evening as well as in overnight consolidation (morning compared to evening performance). While duration of slow-wave sleep was nearly comparable between groups, schizophrenia patients showed lower sleep spindle count, reduced delta power during slow-wave sleep, and reduced spindle power during the slow oscillation (SO) up-state. In healthy but not in schizophrenia patients, a linear relationship between overnight memory consolidation and slow-wave sleep duration as well as delta power was evident. No significant effect with respect to the expectation of memory retrieval was evident in our data. Additionally, we observed a negative linear relationship between total number of sleep spindles and ESI score in healthy participants. Discussion/Conclusion: As expected, schizophrenia patients showed deficient overnight verbal declarative memory consolidation as compared to healthy controls. Reduced sleep spindles, delta power, and spindle power during the SO up-state may link sleep and memory deficiency in schizophrenia. Additionally, the absence of a linear relationship between sleep-related memory consolidation and slow-wave sleep as well as delta power suggests further functional impairments in schizophrenia. Note that this conclusion is based on observational data. Future studies should investigate if stimulation of delta waves during sleep could improve memory performance and thereby quality of life in schizophrenia.

Altered Sleep-Related Consolidation and Neurocognitive Comorbidity in CECTS.

Our aim is to use neurophysiological sleep-related consolidation (SRC) phenomena to identify putative pathophysiological mechanisms in CECTS linked to diffuse neurocognitive deficits. We argue that there are numerous studies on the association between seizure aspects and neurocognitive functioning but not as many on interictal variables and neurocognitive deficits. We suggest two additional foci. First, the interictal presentation in CECTS and second, neuronal oscillations involved in SRC processes. Existing data on mechanisms through which interictal epileptiform spikes (IES) impact upon SRC indicate that they have the potential to: (a) perturb cross-regional coupling of neuronal oscillations, (b) mimic consolidation processes, (c) alter the precision of the spatiotemporal coupling of oscillations, and (d) variably impact upon SRC performance. Sleep spindles merit systematic study in CECTS in order to clarify: (a) the state of the slow oscillations (SOs) with which they coordinate, (b) the precision of slow oscillation-spindle coupling, and (c) whether their developmental trajectories differ from those of healthy children. We subsequently review studies on the associations between IES load during NREM sleep and SRC performance in childhood epilepsy. We then use sleep consolidation neurophysiological processes and their interplay with IES to help clarify the diffuse neurocognitive deficits that have been empirically documented in CECTS. We claim that studying SRC in CECTS will help to clarify pathophysiological mechanisms toward diverse neurocognitive deficits. Future developments could include close links between the fields of epilepsy and sleep, as well as new therapeutic neurostimulation targets. At the clinical level, children diagnosed with CECTS could benefit from close monitoring with respect to epilepsy, sleep and neurocognitive functions.

Improving consolidation by applying anodal transcranial direct current stimulation at primary motor cortex during repetitive practice

Engagement of primary motor cortex (M1) is important for successful consolidation of motor skills. Recruitment of M1 has been reported to be more extensive during interleaved compared to repetitive practice and this differential recruitment has been proposed to contribute to the long-term retention benefit associated with interleaved practice. The present study administered anodal direct current stimulation (tDCS) during repetitive practice in an attempt to increase M1 activity throughout repetitive practice with the goal to improve the retention performance of individuals exposed to this training format. Fifty-four participants were assigned to one of three experimental groups that included: interleaved-sham, repetitive-sham, and repetitive-anodal tDCS. Real or sham stimulation at M1 was administered during practice of three motor sequences for approximately 20-min. Performance in the absence of any stimulation was evaluated prior to practice, immediately after practice as well as at 6-hr, and 24-h after practice was complete. As expected, for the sham conditions, interleaved as opposed repetitive practice resulted in superior offline gain. This was manifest as more rapid stabilization of performance after 6-h as well as an enhancement in performance with a period of overnight sleep. Administration of anodal stimulation at M1 during repetitive practice improved offline gains assessed at both 6-h and 24-h tests compared to the repetitive practice sham group. These data are consistent with the claims that reduced activation at M1 during repetitive practice impedes offline gain relative to interleaved practice and that M1 plays an important role in early consolidation of novel motor skills even in the context of the simultaneous acquisition of multiple new skills. Moreover, these findings highlight a possible role for M1 during sleep-related consolidation, possibly as part of a network including the dorsal premotor region, which supports delayed performance enhancement.

Electrophysiological signatures of memory reactivation in humans.

The reactivation of neural activity that was present during the encoding of an event is assumed to be essential for human episodic memory retrieval and the consolidation of memories during sleep. Pioneering animal work has already established a crucial role of memory reactivation to prepare and guide behaviour. Research in humans is now delineating the neural processes involved in memory reactivation during both wakefulness and sleep as well as their functional significance. Focusing on the electrophysiological signatures of memory reactivation in humans during both memory retrieval and sleep-related consolidation, this review provides an overview of the state of the art in the field. We outline recent advances, methodological developments and open questions and specifically highlight commonalities and differences in the neuronal signatures of memory reactivation during the states of wakefulness and sleep.This article is part of the Theo Murphy meeting issue ‘Memory reactivation: replaying events past, present and future’.

Glucocorticoid response to stress induction prior to learning is negatively related to subsequent motor memory consolidation.

Hippocampal activity during early motor sequence learning is critical to trigger subsequent sleep-related consolidation processes. Based on previous evidence that stress-induced cortisol release modulates hippocampal activity, the current study investigates whether exposure to stress prior to motor sequence learning influences the ensuing learning and overnight consolidation process. Seventy-four healthy young adults were exposed to a stressor (i.e., the socially evaluated cold pressor test, SECPT) or a control procedure before initial training on a bimanual motor sequence learning task. Participants were retested on the motor task 24 h (including a night of sleep) after training to assess memory consolidation. Our results indicate that the SECPT, as compared to the control condition, induced significant physiological stress responses as evidenced by increased heart rate and blood pressure as well as elevated salivary cortisol concentrations. Cortisol concentration in the stress group reached peak levels immediately before and stayed significantly elevated for the full duration of initial motor learning before returning to baseline during the consolidation period. Stress induction prior to learning did not, on average, influence initial performance nor subsequent motor memory consolidation as indicated by similar overnight gains in performance in both groups. However, higher levels of stress-induced cortisol prior to training were correlated to smaller overnight gains in performance speed. These results indicate that the glucocorticoid response to a stressful encounter experienced prior to hippocampal-mediated motor learning is negatively related to subsequent memory consolidation processes.

Curiosity-driven memory enhancement persists over time but does not benefit from post-learning sleep

ABSTRACTSleep-dependent memory processing is dependent on several factors at learning, including emotion, encoding strength, and knowledge of future relevance. Recent work documents the role of curiosity on learning, showing that memory associated with high-curiosity encoding states is retained better and that this effect may be driven by activity within the dopaminergic circuit. Here, we examined whether this curiosity effect was enhanced by or dependent on sleep-related consolidation. Participants learned the answers to trivia questions that they had previously rated on a curiosity scale, and they were shown faces between each question and answer presentation. Memory for these answers and faces was tested either immediately or after a 12-hour delay containing sleep or wakefulness, and polysomnography data was collected for a subset of the sleep participants. Although the curiosity effect for both the answers and incidentally-learned faces was replicated in immediate tests and after the 12-hour delay, the effect was not impacted by the presence of sleep in either case, nor did the effect show a relationship with total sleep time or time in slow-wave sleep. This study suggests that curiosity may be a learning factor that is not subsequently affected by sleep-dependent memory consolidation, but more work ought to examine the role of sleep on curiosity-driven memory in other contexts.

The role of sleep in emotional memory processing in middle age

Sleep benefits memory in young adults, and this effect may be particularly strong for representations associated with negative emotion. Many aspects of sleep important for memory consolidation change with aging, particularly by middle age, suggesting that sleep-related consolidation may be reduced. However, the influence of sleep on memory has rarely been investigated in a middle-aged population. In the current study, young and middle-aged adults viewed negative and neutral pictures and underwent a recognition test after sleep or wake. Subjective emotional reactivity was also measured. Compared to waking, sleep benefited memory in young adults. Performance did not differ between sleep and wake groups in middle-aged adults, and it matched the level of young adults who slept. The effect of sleep versus wake was not influenced by memory valence in either age group. These results suggest the relative influence of sleep compared to wake on memory declines with aging, specifically by middle age, and that this decline extends to negative memory.

Resting-state connectivity after visuo-motor skill learning is inversely associated with offline consolidation in Parkinson's disease and healthy controls

Procedural memory refers to skills acquired through practice and depends on cortico-striatal and cortico-cerebellar circuits. These circuits are typically affected in Parkinson's disease (PD), leading to impaired skill learning, including defective offline consolidation, early in the course of the disease. Evidence points to a role of slow oscillations (<4 Hz) during sleep for offline consolidation. However recent studies showed consolidation over the course of the day, suggesting that consolidation may arise during wakefulness, too. Here we investigate whether functional connectivity (FC) at rest after visuo-motor skill learning is associated with the extent of offline improvements in healthy controls and PD patients. Nineteen participants (9 PD, 10 healthy controls) performed a mirror-drawing task. High-density 156-channel resting state EEG was recorded before and immediately after training. Performance on the task was measured again 24 h later to test for offline consolidation. Delta-band (1–3.5 Hz) FC centered on the left parietal cortex after training predicted offline consolidation. Weak FC was observed in most healthy controls and associated with marked overnight improvement, while strong FC was observed in most PD patients and associated with weak offline consolidation or loss of the skill. These findings indicate that offline consolidation starts immediately after visuo-motor skill learning in brain regions and frequencies typically involved in sleep-related consolidation.

Remembering specific features of emotional events across time: The role of REM sleep and prefrontal theta oscillations.

When an episode of emotional significance is encountered, it often results in the formation of a highly resistant memory representation that is easily retrieved for many succeeding years. Recent research shows that beyond generic consolidation processes, rapid eye movement (REM) sleep importantly contributes to this effect. However, the boundary conditions of consolidation processes during REM sleep, specifically whether these extend to source memory, have not been examined extensively. The current study tested the effects of putative consolidation processes emerging during REM sleep and slow wave sleep (SWS) on item and source memory of negative and neutral images, respectively. Results demonstrate superior emotional relative to neutral item memory retention after both late night REM sleep and early night SWS. Emotional source memory, on the other hand, exhibited an attenuated decline following late night REM sleep, whereas neutral source memory was selectively preserved across early night SWS. This pattern of results suggests a selective preservation of emotional source memory during REM sleep that is functionally dissociable from SWS-dependent reprocessing of neutral source memory. This was further substantiated by a neurophysiological dissociation: Postsleep emotional source memory was selectively correlated with frontal theta lateralization (REM sleep), whereas postsleep neutral item memory was correlated with SWS spindle power. As such, the present results contribute to a more comprehensive characterization of sleep-related consolidation mechanisms underlying emotional and neutral memory retention. Subsidiary analysis of emotional reactivity to previously encoded material revealed an enhancing rather than attenuating effect of late night REM sleep on emotional responses.

Sleep-Driven Computations in Speech Processing.

Acquiring language requires segmenting speech into individual words, and abstracting over those words to discover grammatical structure. However, these tasks can be conflicting—on the one hand requiring memorisation of precise sequences that occur in speech, and on the other requiring a flexible reconstruction of these sequences to determine the grammar. Here, we examine whether speech segmentation and generalisation of grammar can occur simultaneously—with the conflicting requirements for these tasks being over-come by sleep-related consolidation. After exposure to an artificial language comprising words containing non-adjacent dependencies, participants underwent periods of consolidation involving either sleep or wake. Participants who slept before testing demonstrated a sustained boost to word learning and a short-term improvement to grammatical generalisation of the non-adjacencies, with improvements after sleep outweighing gains seen after an equal period of wake. Thus, we propose that sleep may facilitate processing for these conflicting tasks in language acquisition, but with enhanced benefits for speech segmentation.

Brain stimulation during an afternoon nap boosts slow oscillatory activity and memory consolidation in older adults

Sleep-related consolidation of declarative memories, as well as associated neurophysiological events such as slow oscillatory and spindle activity, deteriorate in the course of aging. This process is accelerated in neurodegenerative disease. Transcranial slow oscillatory stimulation (so-tDCS) during sleep has been shown to enhance slow oscillatory brain activity and thereby improve memory consolidation in young subjects. Here, we investigated whether so-tDCS applied to older adults during an afternoon nap exerts similar effects.Eighteen older human subjects were assessed using visuo-spatial (picture memory, primary, and location memory) and verbal memory tasks before and after a 90-min nap either comprising weak so-tDCS at 0.75Hz over fronto-central location or sham (no) stimulation in a within-subject design. Electroencephalographic activity was recorded throughout the naps and immediate effects of stimulation on brain activity were evaluated. Here, spectral power within three frequency bands of interest were computed, i.e., slow oscillatory activity, slow spindle and fast spindle activity; in 1-min stimulation-free intervals following 5 stimulation blocks.So-tDCS significantly increased frontal slow oscillatory activity as well as fast spindle activity, and significantly improved picture memory retention after sleep. Retention in the location memory subtask and in the verbal memory task was not affected. These findings may indicate a novel strategy to counteract cognitive decline in aging in a convenient manner during brief daytime naps.

Does Sleep Improve Your Grammar? Preferential Consolidation of Arbitrary Components of New Linguistic Knowledge.

We examined the role of sleep-related memory consolidation processes in learning new form-meaning mappings. Specifically, we examined a Complementary Learning Systems account, which implies that sleep-related consolidation should be more beneficial for new hippocampally dependent arbitrary mappings (e.g. new vocabulary items) relative to new systematic mappings (e.g. grammatical regularities), which can be better encoded neocortically. The hypothesis was tested using a novel language with an artificial grammatical gender system. Stem-referent mappings implemented arbitrary aspects of the new language, and determiner/suffix+natural gender mappings implemented systematic aspects (e.g. tib scoiffesh + ballerina, tib mofeem + bride; ked jorool + cowboy, ked heefaff + priest). Importantly, the determiner-gender and the suffix-gender mappings varied in complexity and salience, thus providing a range of opportunities to detect beneficial effects of sleep for this type of mapping. Participants were trained on the new language using a word-picture matching task, and were tested after a 2-hour delay which included sleep or wakefulness. Participants in the sleep group outperformed participants in the wake group on tests assessing memory for the arbitrary aspects of the new mappings (individual vocabulary items), whereas we saw no evidence of a sleep benefit in any of the tests assessing memory for the systematic aspects of the new mappings: Participants in both groups extracted the salient determiner-natural gender mapping, but not the more complex suffix-natural gender mapping. The data support the predictions of the complementary systems account and highlight the importance of the arbitrariness/systematicity dimension in the consolidation process for declarative memories.

Diminished Nap Effects on Memory Consolidation Are Seen Under Oral Contraceptive Use

Many young females take exogenous hormones as oral contraceptive (OC), a condition rarely controlled for in studies on sleep and memory consolidation even though sex hormones influence consolidation. This study investigated the effects of OCs on sleep-related consolidation of a motor and declarative task, utilizing a daytime nap protocol. Fifteen healthy, young females taking OCs came to the sleep lab for three different conditions: nap with previous learning, wake with previous learning and nap without learning. They underwent each condition twice, once during the ‘pill-active' weeks and once during the ‘pill-free' week, resulting in 6 visits. In all conditions, participants showed a significant off-line consolidation effect, independent of pill week or nap/wake condition. There were no significant differences in sleep stage duration, spindle activity or spectral EEG frequency bands between naps with or without the learning condition. The present data showed a significant off-line enhancement in memory irrespective of potential beneficial effects of a nap. In comparison to previous studies, this may suggest that the use of OCs may enhance off-line memory consolidation in motor and verbal tasks per se. These results stress the importance to control for the use of OCs in studies focusing on memory performance.

Impaired sleep-related consolidation of declarative memories in idiopathic focal epilepsies of childhood

ObjectiveDeclarative memory is consolidated during sleep in healthy children. We tested the hypothesis that consolidation processes are impaired in idiopathic focal epilepsies (IFE) of childhood in association with frequent interictal epileptiform discharges (IEDs) during sleep. MethodsA verbal (word-pair association) and a nonverbal (2D object location) declarative memory task were administrated to 15 children with IFEs and 8 control children 6–12years of age. Patients had either centrotemporal (11 patients) or occipital (4 patients) IEDs. All but 3 patients had a history of unprovoked seizures, and 6 of them were treated with valproate (VPA). The learning procedure (location of object pairs presented on a grid; association of word pairs) was executed in the evening. Retrieval was tested immediately after learning and on the next morning after a night of sleep. Participants were tested twice, once in natural home conditions and one month later in the unfamiliar conditions of the sleep unit under EEG monitoring. ResultsOvernight recall performance was lower in children with IFE than in control children on both tasks (ps<0.05). Performance in home conditions was similar to that in hospital conditions. Higher spike–wave index (SWI) during nonrapid eye movement (NREM) sleep was associated with poorer performance in the nonverbal task (p<0.05). Valproate treatment was not associated with overnight recall performance for both tasks (ps>0.05). ConclusionMemory consolidation is impaired in IFE of childhood. The association between higher SWI during NREM sleep and poorer nonverbal declarative memory consolidation supports the hypothesis that interictal epileptic activity could disrupt sleep memory consolidation.