Sleep-dependent memory consolidation in patients with sleep disorders

Sleep Stage Transitions and Sleep-Dependent Memory Consolidation in Children with Narcolepsy-Cataplexy

Electroencephalographic sleep stage transitions and altered first REM sleep period transitions have been identified as biomarkers of type 1 narcolepsy in adults, but not in children. Studies on memory complaints in narcolepsy have not yet investigated sleep-dependent memory consolidation. We aimed to explore stage transitions; more specifically altered REM sleep transition and its relationship with sleep-dependent memory consolidation in children with narcolepsy. Twenty-one children with narcolepsy-cataplexy and twenty-three healthy control children completed overnight polysomnography and sleep-dependent memory consolidation tests. Overnight transition rates (number of transitions per hour), global relative transition frequencies (number of transitions between a stage and all other stages/total number of transitions × 100), overnight transitions to REM sleep (transition from a given stage to REM/total REM transitions × 100), and altered first REM sleep period transitions (transitions from wake or N1 to the first REM period) were computed. Narcoleptic children had a significantly higher overnight transition rate with a higher global relative transition frequencies to wake. A lower sleep-dependent memory consolidation score found in children with narcolepsy was associated with a higher overnight transition frequency. As observed in narcoleptic adults, 90.48% of narcoleptic children exhibited an altered first REM sleep transition. As in adults, the altered sleep stage transition is also present in children with narcolepsy-cataplexy, and a higher transition rate could have an impact on sleep-dependent memory consolidation. These potential biomarkers could help diagnose type 1 narcolepsy in children more quickly; however, further studies with larger cohorts, including of those with type 2 narcolepsy and hypersomnia, are needed.

The Devastating Effects of Sleep Deprivation on Memory: Lessons from Rodent Models

In this narrative review article, we discuss the role of sleep deprivation (SD) in memory processing in rodent models. Numerous studies have examined the effects of SD on memory, with the majority showing that sleep disorders negatively affect memory. Currently, a consensus has not been established on which damage mechanism is the most appropriate. This critical issue in the neuroscience of sleep remains largely unknown. This review article aims to elucidate the mechanisms that underlie the damaging effects of SD on memory. It also proposes a scientific solution that might explain some findings. We have chosen to summarize literature that is both representative and comprehensive, as well as innovative in its approach. We examined the effects of SD on memory, including synaptic plasticity, neuritis, oxidative stress, and neurotransmitters. Results provide valuable insights into the mechanisms by which SD impairs memory function.

Polysomnographic features of idiopathic restless legs syndrome: a systematic review and meta-analysis of 13 sleep parameters and 23 leg movement parameters

STUDY OBJECTIVES

This study aims to explore the polysomnographically measured sleep and leg movement differences between idiopathic restless legs syndrome (RLS) patients and healthy controls.

METHODS

An electronic literature search was conducted in EMBASE, MEDLINE, all EBM databases, CINAHL, and PsycINFO. Only observational case-control studies were included in the meta-analysis. The differences in 13 sleep parameters and 23 leg movement parameters between RLS patients and healthy controls were explored.

RESULTS

Thirty-eight studies were identified for systematic review, 31 of which were used for meta-analysis. Meta-analyses revealed significant reductions in total sleep time, sleep efficiency, stage N2 and rapid eye movement (REM) sleep percentages, and increases in wake time after sleep onset, stage shifts per hour, stage N1 percentage, REM latency, arousal index, and apnea-hypopnea index. Some leg movement parameters, such as periodic limb movement during sleep (PLMS) index, PLMS sequence duration, number of PLMS sequence, and periodicity index, were higher in RLS patients compared with healthy controls. Further, our meta-analysis revealed a higher PLMS index during non-REM sleep compared with that during REM sleep.

CONCLUSIONS

RLS patients manifest a lightening of sleep, increased sleep fragmentation, and greater sleep-related breathing disruption and limb movements during sleep relative to healthy normal individuals. The distributions of PLMS during a night's sleep may provide more information to clarify the specific characteristics of leg movements in RLS. PLMS in RLS are concentrated in non-REM sleep. The periodicity index may be a more sensitive and specific marker of RLS than the PLMS index.

CITATION

Zhang H, Zhang Y, Ren R, et al. Polysomnographic features of idiopathic restless legs syndrome: a systematic review and meta-analysis of 13 sleep parameters and 23 leg movement parameters. J Clin Sleep Med. 2022;18(11):2561-2575.

Cognitive Function Decline in the Third Trimester of Pregnancy Is Associated with Sleep Fragmentation

During late pregnancy, sleep deterioration is regularly observed. In concert with these observations, in previous studies by other researchers, a slight objective cognitive decline in pregnant women has been found. Sleep is essential for memory consolidation. The hypothesis of the study was that cognitive impairment could be related to sleep deterioration during pregnancy. The study included 19 pregnant women in their third trimester of pregnancy (28−40 weeks, median 33 weeks (IQR 32−37)) recruited at the Department of Gynecology and Obstetrics, Medical University of Warsaw, and 20 non-pregnant women as controls. The assessment was performed using the vocabulary subtest from the Wechsler Adult Intelligence Scale (WAIS), D2 Test of Attention, OSPAN task (Operational Span Task) to assess cognitive performance, actigraphy to examine sleep parameters, and a set of self-report instruments: Athens Insomnia Scale (AIS), Beck Depression Inventory (BDI), Ford Insomnia Response to Stress (FIRST), Regenstein Hyperarousal Scale (HS), and Epworth Sleepiness Scale (ESS). Although there were no differences between the groups in WAIS (p = 0.18), pregnant women had worse scores in working memory capacity (overall number of remembered letters: p = 0.012, WM span index: p = 0.004) and a significantly lower score in attention (p = 0.03). Pregnant women also had lower sleep efficiency (p = 0.001), more awakenings from sleep (p = 0.001), longer average awakenings (p < 0.0001), longer wake after sleep onset (WASO, p < 0.0001), and longer total time in bed (p < 0.0001). In psychological assessment, pregnant women had only a higher FIRST score (p = 0.02). Using mediation analysis, we found that frequent awakening might be the major factor contributing to deterioration in working memory performance, explaining almost 40% of the total effect. In conclusion, sleep fragmentation in the third trimester of pregnancy may impair working memory consolidation. Pregnant women often complain about poor daily performance as well as non-restorative sleep. In this study, we showed that there is a relationship between lower sleep quality in pregnancy and worse cognitive functioning. We can expect a cognitive decline in women with sleep disturbances in pregnancy. Therefore, we should pay more attention to the treatment of sleep disorders in pregnancy.

Reversible Verbal Memory Integration Deficits in Obstructive Sleep Apnoea

When presented with novel but semantically related elements after learning verbal material, healthy participants tend to endorse these items as previously learned. This reflects the normal integration and association of novel verbal information into long-term memory. How obstructive sleep apnoea (OSA) negatively impacts verbal memory performance, and whether deficits are reversible following positive airway pressure (PAP) treatment, remain elusive. We investigated immediate and delayed OSA- and PAP treatment-related effects on verbal memory integration, using a false memory paradigm. Twenty-three patients with OSA learned lists of words semantically related to target non-presented words (1) at baseline after a polysomnography diagnosis night, (2) after a consecutive polysomnography night under PAP titration, and (3) after three months of compliant PAP treatment. At each session, participants learned 10 different lists of words, each list comprising 15 semantically related items. They had then to recognize 15 minutes later (after an intermediate vigilance task) previously learned words within a list including studied words (learned), unstudied but semantically related items (lures), and non-related unstudied items (controls). Sleep quality and fatigue questionnaires, and psychomotor vigilance tests (PVT) were administered at each session. PAP treatment led to OSA remission and improvement in objective and subjective sleep quality. Crucially, recognition of learned and lure words increased after the first night under treatment and remained stable three months later, suggesting successful memory integration and restoration of semantic processes. No treatment-related outcome was found on PVT performance. OSA exerts a detrimental but PAP-reversible effect on verbal learning and semantic memory integration mechanisms underlying the acquisition of novel memory representations.

Sleep and Prospective Memory: A Retrospective Study in Different Clinical Populations

Prospective memory (PM) is essential in everyday life because it concerns the ability to remember to perform an intended action in the future. This ability could be influenced by poor sleep quality, the role of which, however, is still being debated. To examine the role of sleep quality in PM in depth, we decided to perform a retrospective naturalistic study examining different clinical populations with a primary sleep disorder or comorbid low sleep quality. If sleep is important for PM function, we could expect poor sleep to affect PM performance tasks both directly and indirectly. We examined a total of 3600 nights, recorded using actigraphy in participants belonging to the following groups: primary insomnia (731 nights); narcolepsy type 1 (1069 nights); attention deficit hyperactivity disorder (152 nights in children and 239 in adults); severe obesity (232 nights); essential hypertension (226 nights); menopause (143 nights); healthy controls (808 nights). In a naturalistic activity-based PM task, each participant originally wore an actigraph around the non-dominant wrist and was requested to push the event-marker button at two specific times of day: bedtime (activity 1) and get-up time (activity 2). Each clinical group showed significantly lower sleep quality in comparison to the control group. However, only narcolepsy type 1 patients presented a significantly impaired PM performance at get-up time, remembering to push the event-marker button around half the time compared not only to healthy controls but also to the other clinical groups. Overall, the present results seem to point to sleep quality having no effect on the efficiency of a naturalistic activity-based PM task. Moreover, the data indicated that narcolepsy type 1 patients may show a disease-specific cognitive deficit of PM.

The impact of sleep on eyewitness identifications

Sleep aids the consolidation of recently acquired memories. Evidence strongly indicates that sleep yields substantial improvements on recognition memory tasks relative to an equivalent period of wake. Despite the known benefits that sleep has on memory, researchers have not yet investigated the impact of sleep on eyewitness identifications. Eyewitnesses to crimes are often presented with a line-up (which is a type of recognition memory test) that contains the suspect (who is innocent or guilty) and fillers (who are known to be innocent). Sleep may enhance the ability to identify the guilty suspect and not identify the innocent suspect (i.e. discriminability). Sleep may also impact reliability (i.e. the likelihood that the identified suspect is guilty). In the current study, we manipulated the presence or the absence of sleep in a forensically relevant memory task. Participants witnessed a video of a mock crime, made an identification or rejected the line-up, and rated their confidence. Critically, some participants slept between witnessing the crime and making a line-up decision, while others remained awake. The prediction that participants in the sleep condition would have greater discriminability compared to participants in the wake condition was not supported. There were also no differences in reliability.

Incorporation of fragmented visuo-olfactory episodic memory into dreams and its association with memory performance

The question of a possible link between dream content and memory consolidation remains open. After a comprehensive review of the literature, we present novel findings from an experiment testing whether the incorporation of recently learned stimuli into dream reports is associated with improved post-sleep memory performance. Thirty-two high dream recallers freely explored new visuo-olfactory episodes for 3 consecutive days. During the nights following each non-explicit encoding, participants wore a wrist actimeter, and woke up at 5am and their usual waking time to record their dreams (intensity of all oneiric sensory perception was assessed using scales). A total of 120 dreams were reported and elements related to the encoding phase were identified in 37 of them, either learning-related (mainly visual- and rarely olfactory-related elements), or experiment-related (lab- or experimenters-related elements). On the 4^th day, we found that participants with learning-related (n = 16) and participants with learning-related and/or experiment-related dreams (n = 21) had similar odor recognition and odor-evoked episodic memory with the other participants. However, they had significantly better visuo-spatial memory of the episodes in comparison to the other participants. Our results support the hypothesis that the learning phase is loosely incorporated into dreams and that this incorporation is associated with sleep related memory consolidation.

A Serotonin-Modulated Circuit Controls Sleep Architecture to Regulate Cognitive Function Independent of Total Sleep in Drosophila

Both the structure and the amount of sleep are important for brain function. Entry into deep, restorative stages of sleep is time dependent; short sleep bouts selectively eliminate these states. Fragmentation-induced cognitive dysfunction is a feature of many common human sleep pathologies. Whether sleep structure is normally regulated independent of the amount of sleep is unknown. Here, we show that in Drosophila melanogaster, activation of a subset of serotonergic neurons fragments sleep without major changes in the total amount of sleep, dramatically reducing long episodes that may correspond to deep sleep states. Disruption of sleep structure results in learning deficits that can be rescued by pharmacologically or genetically consolidating sleep. We identify two reciprocally connected sets of ellipsoid body neurons that form the heart of a serotonin-modulated circuit that controls sleep architecture. Taken together, these findings define a circuit essential for controlling the structure of sleep independent of its amount.

REM sleep deprivation impairs retrieval, but not reconsolidation, of methamphetamine reward memory in male rats

Susceptibility to interference can be a result of memory retrieval and reconsolidation. Given the fact that addiction develops through the neural mechanisms of learning and memory, it would not be surprising that a consolidated drug reward memory may also be susceptible to interference following retrieval/reconsolidation. Due to the critical role of sleep in memory consolidation, sleep deprivation (SD) has been shown to impair memory. Therefore, the major objective of this study was to investigate the effect of rapid eye movement (REM) sleep deprivation (RSD) on the retrieval and reconsolidation of methamphetamine (METH) reward memory in male rats. The animals were trained to acquire METH-induced CPP (2 mg/kg, i.p.). METH reward memory was then reactivated/retrieved in the drug-paired chamber during a drug-free (memory reactivation) session. A period of 48-h RSD paradigm using the multiple platform technique resulted in persistent deficits in the retrieval of METH reward memory. Nevertheless, the same protocol of RSD, which was conducted immediately after the memory reactivation, did not affect the reconsolidation of METH reward memory. Additionally, the RSD episode induced a temporary potentiation of METH-induced hyperlocomotion. Our findings would seem to suggest that sleep is involved in the retrieval, but not reconsolidation, of METH reward memory. The results may also demonstrate that RSD mimics the effects of METH on locomotor activity. The results of this study, therefore, support the idea that sleep is involved in the processing of METH reward memory which can be considered for further investigations to manage the relapse associated with drug-related memory.

Impaired emotional memory and decision-making following primary insomnia

Previous studies have indicated that sleep plays an important role in emotional memory and decision-making. However, very little attention has been given to emotional memory and decision-making in patients with primary insomnia (PI). We investigated whether PI influences the accuracy of emotional memory and social decision-making.We examined 25 patients with PI and 20 healthy controls (HC) using an emotional picture memory task and the Iowa Gambling Task (IGT). In the emotional picture memory task, participants completed two testing sessions: an emotional picture evaluation and a delayed recognition phase. During the emotional picture evaluation phase, participants were presented with 48 pictures with different valence (16 positive, 16 neutral, and 16 negative), which they had to evaluate for emotional valence and arousal. During the recognition phase, participants were asked to make a yes/no memory assessment of a set of pictures, which contained the 48 target pictures intermingled with 48 non-target pictures.The performance of the participants with PI was the same as that of the HC in the emotional picture evaluation task. However, the PI group showed worse recognition of the positive and neutral pictures than did the HC group, although recognition of negative pictures was similar in the 2 groups. In the IGT, participants in the PI group more frequently selected cards from the risky decks as the game progressed and selected more disadvantageous cards than did participants in the HC group after the first block.Our findings suggest that insomnia had different effects on memory, depending on the valence of the memory. Specifically, memory performance was impaired for positive and neutral items, but the recognition of negative stimuli seemed to be more resistant to the effects of insomnia. Our results also suggest that decision-making, which is known to be mediated by the ventromedial prefrontal cortex, including decision-making under conditions of uncertainty, may be vulnerable in PI.

[Sleep and cognition in children and adolescents]

Sleep and cognition in children and adolescents Abstract. In this review, one of the most important functions of sleep was described: Its role in promoting cognitive processes in children and adolescents. Particularly, studies of older children and adolescents revealed that sleep interacts in a complex manner with cognitive performance. Moreover, it was shown that sleep supports long-term memory even in young children. This is true for many different long-term memory systems such as memory of factual information (declarative memory), language acquisition, and for reward-related learning, but less so for learning motor skills. Clinical implications arise from observing the consequences of sleep deficits in children and adolescents due to early school hours or due to clinical conditions like attention deficits hyperactive disorder (ADHD), sleep apnea syndrome or other sleep disturbances. Current research has only partially shown that the treatment of sleep problems also benefits cognitive and memory performance. Filling this gap remains an opportunity for further research.

The Biology of Forgetting-A Perspective

Pioneering research studies, beginning with those using Drosophila, have identified several molecular and cellular mechanisms for active forgetting. The currently known mechanisms for active forgetting include neurogenesis-based forgetting, interference-based forgetting, and intrinsic forgetting, the latter term describing the brain's chronic signaling systems that function to slowly degrade molecular and cellular memory traces. The best-characterized pathway for intrinsic forgetting includes "forgetting cells" that release dopamine onto engram cells, mobilizing a signaling pathway that terminates in the activation of Rac1/Cofilin to effect changes in the actin cytoskeleton and neuron/synapse structure. Intrinsic forgetting may be the default state of the brain, constantly promoting memory erasure and competing with processes that promote memory stability like consolidation. A better understanding of active forgetting will provide insights into the brain's memory management system and human brain disorders that alter active forgetting mechanisms.

Attention impairments and ADHD symptoms in adult narcoleptic patients with and without hypocretin deficiency

BACKGROUND

Attentional complaints are common in narcolepsy patients and can overlap with daytime sleepiness features. Few studies attempted to characterize attentional domains in narcolepsy leading to controversial results. We aimed to assess the impact of hypocretin deficiency on attentional functioning by comparing performances on the attention network test (ANT) of narcoleptic patients with hypocretin deficiency (narcolepsy type 1-NT1) versus patients without hypocretin deficiency (narcolepsy type 2-NT2) and healthy controls. We also addressed frequency and severity of psychopathological symptoms and their influence on performances on ANT.

METHODS

Twenty-one NT1 patients, fifteen NT2 patients and twenty-two healthy controls underwent the ANT, which allows assessing three separate attentional processes (alerting, orienting and executive control), and a psychometric assessment including questionnaires on attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder, anxiety and depression symptoms.

RESULTS

NT1 and NT2 patients presented with slower reaction times compared to controls. NT1 patients exhibited an impairment of alerting network relative to NT2 and healthy controls, while orienting and executive control networks efficiency were comparable between groups. NT1 and NT2 displayed higher severity of ADHD inattentive domain than controls, NT1 patients also displayed higher severity of ADHD hyperactive domain and depressive symptoms. In NT1, ADHD and depressive symptoms were positively correlated.

CONCLUSIONS

Despite a shared slowing of reaction times in both NT1 and NT2, a selective impairment of alerting network was present only in hypocretin deficient patients. Clinicians should carefully consider attentional deficits and psychopathological symptoms, including ADHD symptoms, in the clinical assessment and management of patients with narcolepsy.

Poor sleep quality affects spatial orientation in virtual environments

Sleep is well known to have a significant impact on learning and memory. Specifically, studies adopting an experimentally induced sleep loss protocol in healthy individuals have provided evidence that the consolidation of spatial memories, as acquired through navigating and orienteering in spatial surroundings, is negatively affected by total sleep loss. Here, we used both objective and subjective measures to characterize individuals' quality of sleep, and grouped participants into either a poor (insomnia-like) or normal (control) sleep quality group. We asked participants to solve a wayfinding task in a virtual environment, and scored their performance by measuring the time spent to reach a target location and the number of wayfinding errors made while navigating. We found that participants with poor sleep quality were slower and more error-prone than controls in solving the task. These findings provide novel evidence that pre-existing sleep deficiencies in otherwise healthy individuals affects negatively the ability to learn novel routes, and suggest that sleep quality should be accounted for among healthy individuals performing experimental spatial orientation tasks in virtual environments.

Sleep apnoea and the neurologist

There is increasing awareness and interest in the complex and extensive inter-relationships between sleep disorders and neurological disorders. This review focuses on the clinical interactions between obstructive sleep apnoea and stroke, headaches, epilepsy, cognition and idiopathic Parkinson's disease. We highlight to the neurologist the importance of taking a sleep history and considering the diagnosis and treatment of obstructive sleep apnoea.

Reduced Sleep Spindles in Schizophrenia: A Treatable Endophenotype That Links Risk Genes to Impaired Cognition?

Although schizophrenia (SZ) is defined by waking phenomena, abnormal sleep is a common feature. In particular, there is accumulating evidence of a sleep spindle deficit. Sleep spindles, a defining thalamocortical oscillation of non-rapid eye movement stage 2 sleep, correlate with IQ and are thought to promote long-term potentiation and enhance memory consolidation. We review evidence that reduced spindle activity in SZ is an endophenotype that impairs sleep-dependent memory consolidation, contributes to symptoms, and is a novel treatment biomarker. Studies showing that spindles can be pharmacologically enhanced in SZ and that increasing spindles improves memory in healthy individuals suggest that treating spindle deficits in patients with SZ may improve cognition. Spindle activity is highly heritable, and recent large-scale genome-wide association studies have identified SZ risk genes that may contribute to spindle deficits and illuminate their mechanisms. For example, the SZ risk gene CACNA1I encodes a calcium channel that is abundantly expressed in the thalamic spindle generator and plays a critical role in spindle activity based on a mouse knockout. Future genetic studies of animals and humans can delineate the role of this and other genes in spindles. Such cross-disciplinary research, by forging empirical links in causal chains from risk genes to proteins and cellular functions to endophenotypes, cognitive impairments, symptoms, and diagnosis, has the potential to advance the mechanistic understanding, treatment, and prevention of SZ. This review highlights the importance of deficient sleep-dependent memory consolidation among the cognitive deficits of SZ and implicates reduced sleep spindles as a potentially treatable mechanism.

Sleep-dependent memory consolidation in healthy aging and mild cognitive impairment

Sleep quality and architecture as well as sleep's homeostatic and circadian controls change with healthy aging. Changes include reductions in slow-wave sleep's (SWS) percent and spectral power in the sleep electroencephalogram (EEG), number and amplitude of sleep spindles, rapid eye movement (REM) density and the amplitude of circadian rhythms, as well as a phase advance (moved earlier in time) of the brain's circadian clock. With mild cognitive impairment (MCI) there are further reductions of sleep quality, SWS, spindles, and percent REM, all of which further diminish, along with a profound disruption of circadian rhythmicity, with the conversion to Alzheimer's disease (AD). Sleep disorders may represent risk factors for dementias (e.g., REM Behavior Disorder presages Parkinson's disease) and sleep disorders are themselves extremely prevalent in neurodegenerative diseases. Working memory , formation of new episodic memories, and processing speed all decline with healthy aging whereas semantic, recognition, and emotional declarative memory are spared. In MCI, episodic and working memory further decline along with declines in semantic memory. In young adults, sleep-dependent memory consolidation (SDC) is widely observed for both declarative and procedural memory tasks. However, with healthy aging, although SDC for declarative memory is preserved, certain procedural tasks, such as motor-sequence learning, do not show SDC. In younger adults, fragmentation of sleep can reduce SDC, and a normative increase in sleep fragmentation may account for reduced SDC with healthy aging. Whereas sleep disorders such as insomnia, obstructive sleep apnea, and narcolepsy can impair SDC in the absence of neurodegenerative changes, the incidence of sleep disorders increases both with normal aging and, further, with neurodegenerative disease. Specific features of sleep architecture, such as sleep spindles and SWS are strongly linked to SDC. Diminution of these features with healthy aging and their further decline with MCI may account for concomitant declines in SDC. Notably these same sleep features further markedly decline, in concert with declining cognitive function, with the progression to AD. Therefore, progressive changes in sleep quality, architecture, and neural regulation may constitute a contributing factor to cognitive decline that is seen both with healthy aging and, to a much greater extent, with neurodegenerative disease.

Sleep, cognition, and normal aging: integrating a half century of multidisciplinary research

Sleep is implicated in cognitive functioning in young adults. With increasing age, there are substantial changes to sleep quantity and quality, including changes to slow-wave sleep, spindle density, and sleep continuity/fragmentation. A provocative question for the field of cognitive aging is whether such changes in sleep physiology affect cognition (e.g., memory consolidation). We review nearly a half century of research across seven diverse correlational and experimental domains that historically have had little crosstalk. Broadly speaking, sleep and cognitive functions are often related in advancing age, though the prevalence of null effects in healthy older adults (including correlations in the unexpected, negative direction) indicates that age may be an effect modifier of these associations. We interpret the literature as suggesting that maintaining good sleep quality, at least in young adulthood and middle age, promotes better cognitive functioning and serves to protect against age-related cognitive declines.

The link between sleep disturbance and depression among Mexican Americans: a Project FRONTIER study

OBJECTIVE

To examine the link between disturbed sleep and depression scores in Mexican Americans and non-Hispanic Whites.

METHODS

Data were analyzed for 566 participants (45% Mexican Americans) who were part of a rural healthcare study, Project FRONTIER. Mean age was 55.5 years for Mexican Americans (70% female) and 65.6 years for non-Hispanic Whites (69% female). Self-reported sleep disturbance was entered as the predictor, GDS-30 total and factor scores as the outcome variables, and age, sex, education, BMI, and medical diagnoses (hyperlipidemia, diabetes mellitus, and hypertension) entered as covariates.

RESULTS

Mexican Americans reported higher rates of sleep disturbances (25%) than non-Hispanic whites (17%). Sleep disturbances were significantly associated with GDS-30 total scores and the factors Dysphoria and Cognitive Impairment in both Mexican Americans and non-Hispanic whites.

CONCLUSIONS

In this study, Mexican Americans reported higher rates of sleep disturbances than non-Hispanic whites. Disturbed sleep was positively associated with depression and the factor scores for Dysphoria and Cognitive Impairment in both groups. Given the paucity of research on sleep disorders in Mexican Americans, identifying what sleep disorders are present and the impact treating these sleep disorders have on depression warrant further investigation.

Sleep, plasticity and the pathophysiology of neurodevelopmental disorders: the potential roles of protein synthesis and other cellular processes

Sleep is important for neural plasticity, and plasticity underlies sleep-dependent memory consolidation. It is widely appreciated that protein synthesis plays an essential role in neural plasticity. Studies of sleep-dependent memory and sleep-dependent plasticity have begun to examine alterations in these functions in populations with neurological and psychiatric disorders. Such an approach acknowledges that disordered sleep may have functional consequences during wakefulness. Although neurodevelopmental disorders are not considered to be sleep disorders per se, recent data has revealed that sleep abnormalities are among the most prevalent and common symptoms and may contribute to the progression of these disorders. The main goal of this review is to highlight the role of disordered sleep in the pathology of neurodevelopmental disorders and to examine some potential mechanisms by which sleep-dependent plasticity may be altered. We will also briefly attempt to extend the same logic to the other end of the developmental spectrum and describe a potential role of disordered sleep in the pathology of neurodegenerative diseases. We conclude by discussing ongoing studies that might provide a more integrative approach to the study of sleep, plasticity, and neurodevelopmental disorders.

Sleep-related declarative memory consolidation and verbal replay during sleep talking in patients with REM sleep behavior disorder

Objective

To determine if sleep talkers with REM sleep behavior disorder (RBD) would utter during REM sleep sentences learned before sleep, and to evaluate their verbal memory consolidation during sleep.

Methods

Eighteen patients with RBD and 10 controls performed two verbal memory tasks (16 words from the Free and Cued Selective Reminding Test and a 220-263 word long modified Story Recall Test) in the evening, followed by nocturnal video-polysomnography and morning recall (night-time consolidation). In 9 patients with RBD, daytime consolidation (morning learning/recall, evening recall) was also evaluated with the modified Story Recall Test in a cross-over order. Two RBD patients with dementia were studied separately. Sleep talking was recorded using video-polysomnography, and the utterances were compared to the studied texts by two external judges.

Results

Sleep-related verbal memory consolidation was maintained in patients with RBD (+24±36% words) as in controls (+9±18%, p=0.3). The two demented patients with RBD also exhibited excellent nighttime consolidation. The post-sleep performance was unrelated to the sleep measures (including continuity, stages, fragmentation and apnea-hypopnea index). Daytime consolidation (-9±19%) was worse than night-time consolidation (+29±45%, p=0.03) in the subgroup of 9 patients with RBD. Eleven patients with RBD spoke during REM sleep and pronounced a median of 20 words, which represented 0.0003% of sleep with spoken language. A single patient uttered a sentence that was judged to be semantically (but not literally) related to the text learned before sleep.

Conclusion

Verbal declarative memory normally consolidates during sleep in patients with RBD. The incorporation of learned material within REM sleep-associated sleep talking in one patient (unbeknownst to himself) at the semantic level suggests a replay at a highly cognitive creative level.