The memory function of sleep

A review of the application of exercise intervention on improving cognition in patients with Alzheimer's disease: mechanisms and clinical studies

Alzheimer's disease (AD) is the most common form of dementia, leading to sustained cognitive decline. An increasing number of studies suggest that exercise is an effective strategy to promote the improvement of cognition in AD. Mechanisms of the benefits of exercise intervention on cognitive function may include modulation of vascular factors by affecting cardiovascular risk factors, regulating cardiorespiratory health, and enhancing cerebral blood flow. Exercise also promotes neurogenesis by stimulating neurotrophic factors, affecting neuroplasticity in the brain. Additionally, regular exercise improves the neuropathological characteristics of AD by improving mitochondrial function, and the brain redox status. More and more attention has been paid to the effect of Aβ and tau pathology as well as sleep disorders on cognitive function in persons diagnosed with AD. Besides, there are various forms of exercise intervention in cognitive improvement in patients with AD, including aerobic exercise, resistance exercise, and multi-component exercise. Consequently, the purpose of this review is to summarize the findings of the mechanisms of exercise intervention on cognitive function in patients with AD, and also discuss the application of different exercise interventions in cognitive impairment in AD to provide a theoretical basis and reference for the selection of exercise intervention in cognitive rehabilitation in AD.

Association between slow wave sleep and blood pressure in insomnia

STUDY OBJECTIVES

The majority of patients with insomnia exhibit abnormal sleep in objective testing (e.g. decreased sleep duration, decreased slow wave sleep [SWS]). Previous studies have suggested that some of these objective measures of poor sleep, such as decreased sleep duration, are associated with a higher risk of hypertension in insomnia. We examined the relationship between SWS and morning and evening blood pressure (BP) levels in patients with clinically diagnosed insomnia.

METHODS

A total of 229 normal sleepers and 1378 insomnia patients were included in this study. Insomnia was defined based on standard diagnostic criteria with symptoms lasting ≥6 months. All participants underwent in-laboratory polysomnography. Patients were classified into quartiles of percent SWS. Evening and morning hypertension were defined using BP measurements taken in the evening before and in the morning after polysomnography, respectively. Multivariable logistic regression models were used to assess the relationship between insomnia, SWS, and hypertension.

RESULTS

Insomniacs with <3.5% SWS (OR 3.27, 95% confidence intervals [CI]: 1.31 to 7.66) and those with 3.5%-10.2% SWS (OR 2.38, 95% CI: 1.28 to 5.91) had significantly greater odds of morning hypertension compared to normal sleepers. No associations were seen in insomnia with 10.2%-15.8% SWS and with >15.8% SWS. Significant effect modifications by sex (p = .043) were found, as decreased SWS was associated with morning hypertension only in men. Odds of evening hypertension were not significantly associated with SWS.

CONCLUSIONS

Decreased SWS is associated with morning hypertension in a dose-dependent manner in insomnia, especially in men.

A potential candidate for prevention of PTSD: Prazosin prevents learned helplessness behavior in adult male rats

Post-Traumatic Stress Disorder (PTSD) is a debilitating psychiatric disorder that arises following exposure to an extreme stress. PTSD is characterized by five primary trauma-related symptom clusters, including symptoms of negative mood and hyperresponsivity to the traumatic event. Regrettably, the current therapy options are not highly effective. Therefore, prevention of PTSD is crucial and potentially applicable. Prazosin is an anti-adrenergic medication that is used to reduce nightmares in patient with PTSD, and can also mitigate the noradrenergic dysfunction caused by trauma. Here we show that administration of prazosin prior to the trauma prevented learned helplessness behavior in adult male rats. We show that the animals that were exposed to three days of inescapable foot shocks preceded by prazosin injections have fewer prazosin-treated animals showing learned helplessness compared to saline-treated animals. Nevertheless, there was no significant difference in anxiety-related behavior as measured in the elevated plus maze. Furthermore, the results of in vivo electrophysiological recordings of the ventral tegmental area shows that the prazosin group has a trend of increased number of active dopaminergic cells per track; this is significant when limited to central region of the ventral tegmental area. Our results demonstrate that prazosin has a potential for prevention of PTSD.

Bilingualism, sleep, and cognition: An integrative view and open research questions

Sleep and language are fundamental to human existence and have both been shown to substantially affect cognitive functioning including memory, attentional performance, and cognitive control. Surprisingly, there is little-to-no research that examines the shared impact of bilingualism and sleep on cognitive functions. In this paper, we provide a general overview of existing research on the interplay between bilingualism and sleep with a specific focus on executive functioning. First, we highlight their interconnections and the resulting implications for cognitive performance. Second, we emphasize the need to explore how bilingualism and sleep intersect at cognitive and neural levels, offering insights into potential ways of studying the interplay between sleep, language learning, and bilingual language use. Finally, we suggest that understanding these relationships could enhance our knowledge of reserve and its role in mitigating age-related cognitive decline.

Melatonin: A potential nighttime guardian against Alzheimer's

In the context of the escalating global health challenge posed by Alzheimer's disease (AD), this comprehensive review considers the potential of melatonin in both preventive and therapeutic capacities. As a naturally occurring hormone and robust antioxidant, accumulating evidence suggests melatonin is a compelling candidate to consider in the context of AD-related pathologies. The review considers several mechanisms, including potential effects on amyloid-beta and pathologic tau burden, antioxidant defense, immune modulation, and regulation of circadian rhythms. Despite its promise, several gaps need to be addressed prior to clinical translation. These include conducting additional randomized clinical trials in patients with or at risk for AD dementia, determining optimal dosage and timing, and further determining potential side effects, particularly of long-term use. This review consolidates existing knowledge, identifies gaps, and suggests directions for future research to better understand the potential of melatonin for neuroprotection and disease mitigation within the landscape of AD.

Sleep microstructure organizes memory replay

Recently acquired memories are reactivated in the hippocampus during sleep, an initial step for their consolidation1-3. This process is concomitant with the hippocampal reactivation of previous memories4-6, posing the problem of how to prevent interference between older and recent, initially labile, memory traces. Theoretical work has suggested that consolidating multiple memories while minimizing interference can be achieved by randomly interleaving their reactivation7-10. An alternative is that a temporal microstructure of sleep can promote the reactivation of different types of memories during specific substates. Here, to test these two hypotheses, we developed a method to simultaneously record large hippocampal ensembles and monitor sleep dynamics through pupillometry in naturally sleeping mice. Oscillatory pupil fluctuations revealed a previously unknown microstructure of non-REM sleep-associated memory processes. We found that memory replay of recent experiences dominated in sharp-wave ripples during contracted pupil substates of non-REM sleep, whereas replay of previous memories preferentially occurred during dilated pupil substates. Selective closed-loop disruption of sharp-wave ripples during contracted pupil non-REM sleep impaired the recall of recent memories, whereas the same manipulation during dilated pupil substates had no behavioural effect. Stronger extrinsic excitatory inputs characterized the contracted pupil substate, whereas higher recruitment of local inhibition was prominent during dilated pupil substates. Thus, the microstructure of non-REM sleep organizes memory replay, with previous versus new memories being temporally segregated in different substates and supported by local and input-driven mechanisms, respectively. Our results suggest that the brain can multiplex distinct cognitive processes during sleep to facilitate continuous learning without interference.

Influence of sleep on seizures and interictal epileptiform discharges in epilepsy

Sleep significantly influences seizure occurrence and interictal epileptiform discharges (IEDs) in patients with epilepsy. Sleep-related epilepsy, where seizures occur exclusively or predominantly during sleep, has been observed in various epilepsy syndromes. Understanding the influence of sleep on seizures and IEDs is crucial in the diagnosis, classification, and management of epilepsy. Although there is a bidirectional relationship between sleep and epilepsy, this review focuses on the influence of sleep on seizures and IEDs in epilepsy. Seizures are more common during non-rapid eye movement (NREM) sleep, particularly during stage N2, and are suppressed during rapid eye movement (REM) sleep. Sleep also activates IEDs, increasing the diagnostic yield of EEG recordings. The rate of IEDs increases during NREM sleep, reaches its maximum during stage N3, and decreases during REM sleep. Sleep affects the electrical field of IEDs, with an increase of spiking fields during NREM sleep and a decrease during REM sleep. In the localization of epileptogenic foci, REM sleep is less sensitive but more specific than NREM sleep. Thalamocortical EEG synchronization during NREM sleep and desynchronization during REM sleep underlie their opposing effects on seizures and IEDs. Accumulating evidence has suggested an antiseizure effect of orexinergic antagonism in animal studies. Interventions that promote REM sleep, including orexinergic antagonists, should be studied in the future as novel treatment strategies for epilepsy.

Role of sleep and neurochemical biomarkers in synaptic plasticity related to neurological and psychiatric disorders: A scoping review

Sleep is vital for maintaining physical and mental well-being, impacting cognitive functions like memory and learning through neuroplasticity. Sleep disturbances prevalent in neurological and psychiatric disorders exacerbate cognitive decline, imposing societal burdens. Exploring the relationship between sleep and neuroplasticity elucidates the mechanisms influencing cognition, particularly amidst the prevalent sleep disturbances in these clinical populations. While existing reviews provide valuable insights, gaps remain in understanding the neurophysiological mechanisms underlying sleep and cognitive function. This scoping review aims to investigate the characteristic patterns of sleep parameters and neurochemical biomarkers in reflecting neuroplasticity changes related to neurological and psychiatric disorders and to explore how these markers interact and influence cognition at the molecular level. Studies involving adults and older adults were included, excluding animal models and the paediatric population. Selected studies explored the relationship between sleep parameter or neurochemical biomarker changes and cognitive impairment, reflecting underlying neuroplasticity changes. Peer-reviewed articles, clinical trials, theses, and dissertations in English were included while excluding secondary research and non-peer-reviewed sources. A three-step search strategy was executed following the updated Joanna Briggs Institute methodology for scoping reviews. Published studies were retrieved from nine databases, grey literature, expert recommendations, and hand-searching of the included studies' bibliography. A basic qualitative content synthesis of 34 studies was conducted per JBI's scoping review guidance. Slow-wave and Rapid-Eye Movement sleep, sleep spindles, sleep cycle disruption, K-Complex(KC) density, Hippocampal sEEG, BDNF, IL-6, iNOS mRNA expression, plasma serotonin, CSF Aβ-42, t-tau and p-tau proteins, and serum cortisol revealed associations with cognitive dysfunction. Examining the relationship between sleep parameters, neurochemical biomarkers, and cognitive function reveals neuronal mechanisms that guide potential therapeutic interventions and enhance quality patient care.

Breathing orchestrates synchronization of sleep oscillations in the human hippocampus

Nested sleep oscillations, emerging from asynchronous states in coordinated bursts, are critical for memory consolidation. Whether these bursts emerge intrinsically or from an underlying rhythm is unknown. Here, we show a previously undescribed respiratory-driven oscillation in the human hippocampus that couples with cardinal sleep oscillations. Further, breathing promotes nesting of ripples in slow oscillations, together suggesting that respiration acts as an intrinsic rhythm to coordinate synchronization of sleep oscillations, providing a unique framework to characterize sleep-related respiratory and memory processes.

Oral administration of ethinyl estradiol and the brain-selective estrogen prodrug DHED in a female common marmoset model of menopause: Effects on cognition, thermoregulation, and sleep

Menopausal symptoms of sleep disturbances, cognitive deficits, and hot flashes are understudied, in part due to the lack of animal models in which they co-occur. Common marmosets (Callithrix jacchus) are valuable nonhuman primates for studying these symptoms, and we examined changes in cognition (reversal learning), sleep (48 h/wk of sleep recorded by telemetry), and thermoregulation (nose temperature in response to mild external warming) in middle-aged, surgically-induced menopausal marmosets studied at baseline, during 3-week phases of ethinyl estradiol (EE2, 4 μg/kg/day, p.o.) treatment and after EE2 withdrawal. We also assessed a brain-selective hormonal therapy devoid of estrogenic effects in peripheral tissues on the same measures (cognition, sleep, thermoregulation) after treatment with the estrogen prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED, 100 μg/kg/day, p.o) and DHED withdrawal. Reversal learning performance was improved with EE2 or DHED treatment relative to phases without hormone administration, as indicated by a faster reversal of the stimulus/reward contingencies. Both EE2 and DHED increased non-REM sleep and reduced nighttime awakenings relative to baseline, but to the detriment of REM sleep which was highest at baseline. Nasal temperature in response to mild external warming was highest, and overnight core body temperature lowest, in the DHED treatment phase compared to both the EE2 and baseline phases. These results suggest that low dose estradiol, delivered either peripherally or centrally via DHED, benefits selective aspects of cognition and sleep in a marmoset menopause model. DHED appears a promising therapeutic candidate for alleviating the cognitive and sleep disruptions associated with estrogen deficiency in primates.

Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) Demonstrates That Sleep Disorders Exacerbate Glymphatic Circulatory Impairment and Cognitive Impairment in Patients with Alzheimer's Disease

Objective

Sleep disorders are common in Alzheimer's disease (AD) patients and can impair the glymphatic system, leading to cognitive decline. This study aimed to investigate whether AD patients with sleep disorders exhibit worse glymphatic function and more severe cognitive impairment compared to those without sleep disorders and to explore the underlying molecular imaging mechanisms.

Methods

This study included 40 AD patients with sleep disorders (ADSD), 39 cognitively matched AD patients without sleep disorders (ADNSD), and 25 healthy middle-aged and elderly controls (NC). Participants underwent functional magnetic resonance imaging (fMRI), and cognitive and sleep assessments. The ALPS (Along the Perivascular Space) index was calculated, followed by intergroup comparisons, correlation analyses, and mediation analyses. The diagnostic utility of the ALPS index was assessed using a receiver operating characteristic (ROC) curve.

Results

The ALPS index was lower in the ADNSD and ADSD groups compared to the NC group. In the ADSD group, PSQI scores were negatively correlated with MMSE scores. The ALPS index was positively correlated with MMSE scores and negatively with PSQI scores. Mediation analyses indicated that the ALPS index partially mediated the effect of sleep disturbances on cognitive impairment (indirect effect = -0.134; mediation effect = 30.505%). The area under the ROC curve (AUROC) for distinguishing ADSD from ADNSD was 0.86, with a cutoff ALPS index value 1.309.

Conclusion

Sleep disorders worsen glymphatic function and cognitive impairment in AD patients. The ALPS index partially mediates the impact of sleep disorders on cognitive function and shows moderate accuracy in distinguishing between patients with ADSD and ADNSD.

Detection and location of EEG events using deep learning visual inspection

The electroencephalogram (EEG) is a major diagnostic tool that provides detailed insight into the electrical activity of the brain. This signal contains a number of distinctive waveform patterns that reflect the subject's health state in relation to sleep, neurological disorders, memory functions, and more. In this regard, sleep spindles and K-complexes are two major waveform patterns of interest to specialists, who visually inspect the recordings to identify these events. The literature typically follows a traditional approach that examines the time-varying signal to identify features representing the events of interest. Even though most of these methods target individual event types, their reported performance results leave significant room for improvement. The research presented here adopts a novel approach to visually inspect the waveform, similar to how specialists work, to develop a single model that can detect and determine the location of both sleep spindles and K-complexes. The model then produces bounding boxes that accurately delineate the location of these events within the image. Several object detection algorithms (i.e., Faster R-CNN, YOLOv4, and YOLOX) and multiple backbone CNN architectures were evaluated under a wide range of conditions, revealing their true representative performance. The results show exceptional precision (>95% mAP@50) in detecting sleep spindles and K-complexes, albeit with less consistency across backbones and thresholds for the latter.

Sleep Posture Influences Metabolic Rate and Vigilance in the Common Whitethroat (Curruca Communis)

Migration is an important life-history strategy that is adopted by a significant proportion of bird species from temperate areas. Birds initiate migration after accumulating considerable energy reserves, primarily in the form of fat and muscle. Sustained exercise, such as during the crossing of ecological barriers, leads to the depletion of energy reservesand increased physiological stress. Stopover sites, where birds rest and restore energy, play a fundamental role in mitigating these challenges. The duration of resting at stopover sites is influenced by environmental and physiological conditions upon arrival, and the amount of body fat reserves plays an important role. While sleep is recognized as essential for all organisms, its importance is accentuated during migration, where energy management becomes a survival constraint. Previous research indicated that individuals with larger fat reserves tend to sleep less and favor an untucked sleep posture, influencing energy recovery and anti-predatory vigilance. We explored the relationship between sleep behavior and posture, metabolic state, and energy conservation strategies during migration in the common whitethroat (Curruca communis). We were able to confirm that sleeping in a tucked position results in metabolic energy savings, at the cost of reduced vigilance. However, whitethroats did not show alterations of their sleep patterns as a response to the amount of stored reserves. This suggests that they may not be taking full advantage of the metabolic gains of sleeping in a tucked posture, at least at this stage of their migratory journey. We suggest that, to achieve optimal fuel accumulation and maximize stopover efficiency, whitethroats prioritize increased foraging over modulating their sleep patterns.

Subthalamic γ Oscillation Underlying Rapid Eye Movement Sleep Abnormality in Parkinsonian Patients

BACKGROUND

Abnormal rapid eye movement (REM) sleep, including REM sleep behavior disorder (RBD) and reduced REM sleep, is common in Parkinson's disease (PD), highlighting the importance of further study on REM sleep. However, the biomarkers of REM disturbances remain unknown, leading to the lack of REM-specific neuromodulation interventions.

OBJECTIVE

This study aims to investigate the neurophysiological biomarkers of REM disturbance in parkinsonian patients.

METHODS

Ten PD patients implanted with bilateral subthalamic nucleus-deep brain stimulation (STN-DBS) were included in this study, of whom 4 were diagnosed with RBD. Sleep monitoring was conducted 1 month after surgery. Subthalamic local field potentials (LFP) were recorded through sensing-enabled DBS. The neurophysiological features of subthalamic LFP during phasic and tonic microstates of REM sleep and their correlation with REM sleep fragmentation and RBD were analyzed.

RESULTS

Differences in subthalamic γ oscillation between phasic and tonic REM correlated positively with the severity of REM sleep fragmentation. Patients with RBD also exhibited stronger γ oscillations during REM sleep compared with non-RBD patients, and both increased β and γ were found before the onset of RBD episodes. Stimulation changes in simulated γ-triggered feedback modulation followed more closely with phasic REM density, whereas an opposite trend was found in simulated β-triggered feedback modulation.

CONCLUSION

Excess subthalamic γ oscillations may contribute to REM instability and RBD, suggesting that γ oscillation could serve as a feedback signal for adaptive DBS for REM sleep disorders. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Anesthetic spindles serve as EEG markers of the depth variations in anesthesia induced by multifarious general anesthetics in mouse experiments

Background

Mice play a crucial role in studying the mechanisms of general anesthesia. However, identifying reliable EEG markers for different depths of anesthesia induced by multifarious agents remains a significant challenge. Spindle activity, typically observed during NREM sleep, reflects synchronized thalamocortical activity and is characterized by a frequency range of 7-15 Hz and a duration of 0.5-3 s. Similar patterns, referred to as "anesthetic spindles," are also observed in the EEG during general anesthesia. However, the variability of anesthetic spindles across different anesthetic agents and depths is not yet fully understood.

Method

Mice were anesthetized with dexmedetomidine, propofol, ketamine, etomidate, isoflurane, or sevoflurane, and cortical EEG recordings were obtained. EEG signals were bandpass filtered between 0.1 and 60 Hz and analyzed using a custom MATLAB script for spindle detection. Anesthesia depth was assessed based on Guedel's modified stages of anesthesia and the presence of burst suppression in the EEG.

Results

Compared to sleep spindles, anesthetic spindles induced by the different agents exhibited higher amplitudes and longer durations. Isoflurane- and sevoflurane-induced spindles varied with the depth of anesthesia. Spindles associated with etomidate were prominent during induction and light anesthesia, whereas those induced by sevoflurane and isoflurane were more dominant during deep anesthesia and emergence. Post-anesthesia, spindles persisted but ceased more quickly following inhalational anesthesia.

Conclusion

Anesthesia spindle waves reflect distinct changes in anesthesia depth and persist following emergence, serving as objective EEG markers for assessing both anesthesia depth and the recovery process.

Membrane potential states gate synaptic consolidation in human neocortical tissue

Synaptic mechanisms that contribute to human memory consolidation remain largely unexplored. Consolidation critically relies on sleep. During slow wave sleep, neurons exhibit characteristic membrane potential oscillations known as UP and DOWN states. Coupling of memory reactivation to these slow oscillations promotes consolidation, though the underlying mechanisms remain elusive. Here, we performed axonal and multineuron patch-clamp recordings in acute human brain slices, obtained from neurosurgeries, to show that sleep-like UP and DOWN states modulate axonal action potentials and temporarily enhance synaptic transmission between neocortical pyramidal neurons. Synaptic enhancement by UP and DOWN state sequences facilitates recruitment of postsynaptic action potentials, which in turn results in long-term stabilization of synaptic strength. In contrast, synapses undergo lasting depression if presynaptic neurons fail to recruit postsynaptic action potentials. Our study offers a mechanistic explanation for how coupling of neural activity to slow waves can cause synaptic consolidation, with potential implications for brain stimulation strategies targeting memory performance.

Sleep induced by mechanosensory stimulation provides cognitive and health benefits in Drosophila

STUDY OBJECTIVES

Sleep is a complex phenomenon regulated by various factors, including sensory input. Anecdotal observations have suggested that gentle rocking helps babies fall asleep, and experimental studies have verified that rocking promotes sleep in both humans and mice. Recent studies have expanded this understanding, demonstrating that gentle vibration also induces sleep in Drosophila. Natural sleep serves multiple functions, including learning and memory, synaptic downscaling, and reduction of harmful substances associated with neurodegenerative diseases. Here, we investigated whether vibration-induced sleep (VIS) provides similar cognitive and health benefits in Drosophila.

METHODS

We administered gentle vibration to flies that slept very little due to a forced activation of wake-promoting neurons and investigated how the vibration influenced learning and memory in the courtship conditioning paradigm. Additionally, we examined the effects of VIS on synaptic downscaling by counting synaptic varicosities of select neurons. Finally, we determined whether vibration could induce sleep in Drosophila models of Alzheimer's disease (AD) and suppress the accumulation of Amyloid β (Aβ) and Tubulin Associated Unit (TAU).

RESULTS

VIS enhanced performance in a courtship conditioning paradigm and reduced the number of synaptic varicosities in select neurons. Moreover, vibration improved sleep in Drosophila models of AD, reducing Aβ and TAU levels.

CONCLUSIONS

Mechanosensory stimulation offers a promising noninvasive avenue for enhancing sleep, potentially providing associated cognitive and health benefits.

A meta-analytic investigation of the effect of sleep deprivation on inhibitory control

Sleep deprivation may have a deleterious effect on inhibitory control; however, this effect is not consistent across studies. To arrive at an overall estimate of the relationship between sleep deprivation and inhibitory control, this report used meta-analysis to summarise the magnitude of the effects of sleep deprivation on inhibitory control as measured by the Go/No-Go and Stop Signal Tasks. These are two widely used tasks in the literature. A systematic search of four databases (APAPsycINFO, Medline, CINAHL and Embase) from their inception to November 2023 identified 24 studies involving 712 healthy individuals. Separate random-effects models were used to estimate the effect size of sleep deprivation on performance in these tasks. The meta-analysis revealed a moderate negative effect of sleep deprivation on inhibitory control in both the Go/No-Go and Stop Signal Tasks. Given the importance of inhibitory control in everyday behaviour, future research should investigate the neural and neurophysiological mechanisms underlying this relationship and explore its impact in clinical populations.

Ameliorating Effect of Fermented Perilla frutescens on Sleep Deprivation-Induced Cognitive Impairment Through Antioxidant and BDNF Signaling in Mice

Background: Adequate sleep is essential for maintaining cognitive function, as evidenced by literature. Perilla frutescens var. acuta Kudo (PF) is a traditional medicinal herb reported to improve vascular cognitive impairment and induce sedation. However, the effects of PF on cognitive impairment caused by sleep deprivation (SD) have not yet been evaluated. This study aims to evaluate the effects of fermented PF (FPF) and its underlying mechanisms in a model of SD-induced cognitive impairment. Methods: Mice were subjected to SD to establish cognitive impairment, and FPF was administered once daily for 3 days. Cognitive performance was assessed using Y-maze and passive avoidance tests, followed by molecular mechanisms analyses. Results: FPF treatment improved SD-induced cognitive impairment, as evidenced by increased spontaneous alternation and extended latency time. Histological analysis revealed that SD impaired the hippocampus, and this impairment was alleviated by FPF treatment. FPF demonstrated antioxidant activity by increasing glutathione levels and decreasing malondialdehyde levels. Furthermore, the decreased levels of brain-derived neurotrophic factor (BDNF) observed in sleep-deprived mice were restored with FPF treatment. FPF also enhanced the phosphorylation of tropomyosin receptor kinase B, extracellular signal-regulated kinase, and cAMP response element-binding protein. Conclusions: These results indicate that FPF may have beneficial effects on SD-induced cognitive impairment by protecting against oxidative stress and increasing BDNF expression.

Memory reactivation generates new, adaptive behaviours that reach beyond direct experience

Periods of rest and sleep help us find hidden solutions to new problems and infer unobserved relationships between discrete events. However, the mechanisms that formulate these new, adaptive behavioural strategies remain unclear. One possibility is that memory reactivation during periods of rest and sleep has the capacity to generate new knowledge that extends beyond direct experience. Here, we test this hypothesis using a pre-registered study design that includes a rich behavioural paradigm in humans. We use contextual Targeted Memory Reactivation (TMR) to causally manipulate memory reactivation during awake rest. We demonstrate that TMR during rest enhances performance on associative memory tests, with improved discovery of new, non-directly trained associations, and no change observed for directly trained associations. Our findings suggest that memory reactivation during awake rest plays a critical role in extracting new, unobserved associations to support adaptive behavioural strategies such as inference.

Increase in slow frequency and decrease in alpha and beta power during post-learning rest predict long-term memory success

Formation of episodic memories is linked to cortico-hippocampal interactions during learning, practice, and post-learning rest, although the role of cortical activity itself in such processes remains elusive. Behaviorally, long-term retention of episodic memories has been shown to be aided by several different practice strategies involving memory reencounters, such as repeated retrieval and repeated study. In a two-session resting state electroencephalography (EEG) experiment, using data from 68 participants, we investigated the electrophysiological predictors of long-term memory success in situations where such reencounters occurred after learning. Participants learned word pairs which were subsequently practiced either by cued recall or repeated studying in a between-subjects design. Participants' cortical activity was recorded before learning (baseline) and after practice during 15-min resting periods. Long-term memory retention after a 7-day period was measured. To assess cortical activity, we analyzed the change in spectral power from the pre-learning baseline to the post-practice resting state recordings. From baseline to post-practice, changes in alpha and beta power were negatively, while slow frequency power change was positively associated with long-term memory performance, regardless of practice strategy. These results are in line with previous observations pointing to the role of specific frequency bands in memory formation and extend them to situations where memory reencounters occur after learning. Our results also highlight that the effectiveness of practice by repeated testing seems to be independent from the beneficial neural mechanisms mirrored by EEG frequency power changes.

The claustrum and synchronized brain states

Cortical activity is constantly fluctuating between distinct spatiotemporal activity patterns denoted by changes in brain state. States of cortical desynchronization arise during motor generation, increased attention, and high cognitive load. Synchronized brain states comprise spatially widespread, coordinated low-frequency neural activity during rest and sleep when disengaged from the external environment or 'offline'. The claustrum is a small subcortical structure with dense reciprocal connections with the cortex suggesting modulation by, or participation in, brain state regulation. Here, we highlight recent work suggesting that neural activity in the claustrum supports cognitive processes associated with synchronized brain states characterized by increased low-frequency network activity. As an example, we outline how claustrum activity could support episodic memory consolidation during sleep.

Aging, brain plasticity, and motor learning

Motor skill learning, the process of acquiring new motor skills, is critically important across the lifespan, from early development through adulthood and into older age, as well as in pathological conditions (i.e., rehabilitation). Extensive research has demonstrated that motor skill acquisition in young adults is accompanied by significant neuroplastic changes, including alterations in brain structure (gray and white matter), function (i.e., activity and connectivity), and neurochemistry (i.e., levels of neurotransmitters). In the aging population, motor performance typically declines, characterized by slower and less accurate movements. However, despite these age-related changes, older adults maintain the capacity for skill improvement through training. In this review, we explore the extent to which the aging brain retains the ability to adapt in response to motor learning, specifically whether skill acquisition is accompanied by neural changes. Furthermore, we discuss the associations between inter-individual variability in brain structure and function and the potential for future learning in older adults. Finally, we consider the use of non-invasive brain stimulation techniques aimed at optimizing motor learning in this population. Our review provides insights into the neurobiological underpinnings of motor learning in older adults and emphasizes strategies to enhance their motor skill acquisition.

A systematic and meta-analytic review of the impact of sleep restriction on memory formation

Modern life causes a quarter of adults and half of teenagers to sleep for less than is recommended (Kocevska et al., 2021). Given well-documented benefits of sleep on memory, we must understand the cognitive costs of short sleep. We analysed 125 sleep restriction effect sizes from 39 reports involving 1234 participants. Restricting sleep (3-6.5 hours) compared to normal sleep (7-11 hours) negatively affects memory formation with a small effect size (Hedges' g = 0.29, 95 % CI = [0.13, 0.44]). We detected no evidence for publication bias. When sleep restriction effect sizes were compared with 185 sleep deprivation effect sizes (Newbury et al., 2021) no statistically significant difference was found, suggesting that missing some sleep has similar consequences for memory as not sleeping at all. When the analysis was restricted to post-encoding, rather than pre-encoding, sleep loss, sleep deprivation was associated with larger memory impairment than restriction. Our findings are best accounted for by the sequential hypothesis which emphasises complementary roles of slow-wave sleep and REM sleep for memory.

The impact of sleep on factual memory retention over 24 hr

Although a period of sleep seems to benefit the retention of declarative memories, recent studies have challenged both the size of this effect and its active influence on memory consolidation. This study aimed to further investigate the effect of sleep and its time dependency on the consolidation of factual information. In a within-subjects design, 48 participants (Mage = 24.37 ± 4.18 years, 31F) were asked to learn several facts in a multi-sensory "flashcard-like" memory task at 21:00 hours (sleep first condition) or at 09:00 hours (wake first condition). Then, in each condition, participants performed an immediate recall test (T0), and two delayed tests 12 hr (T1) and 24 hr (T2) later. Participants' sleep was recorded at their homes with a portable device. Results revealed that memory retention was better after a night of sleep compared with wakefulness, regardless of the delay from encoding (a few hr versus 12+ hr), but the sleep effect was modest. The decline in memory during the wake period following sleep was smaller compared with the decline observed during the 12 hr of wakefulness after encoding. However, after 24 hr from the encoding, when all participants experienced a period of both sleep and wakefulness, memory performance in the two conditions was similar. Overall, our data suggest that sleep exerts a small, yet beneficial, influence on memory retention by likely reducing interference and actively stabilizing memory traces.

The ventral midline thalamus and long-term memory: What consolidation, what retrieval, what plasticity in rodents?

The ventral midline thalamus, including the reuniens and rhomboid (ReRh) nuclei, connects bidirectionally with the medial prefrontal cortex (mPFC) and hippocampus (Hip), both essential for memory processes. This review compiles and discusses studies on a role for the ReRh nuclei in the system consolidation of memories, also considering their potentially limited participation in memory retrieval or early phases of consolidation. It also examines scientific literature on short- and long-term plasticity in ReRh-mPFC and ReRh-Hip connections, emphasizing plasticity's importance in understanding these nuclei's role in memory. The idea that the two nuclei are at the crossroads of information exchange between the mPFC and the Hip is not new, but the relationship between this status and the plasticity of their connections remains elusive. Since this perspective is relatively recent, our concluding section suggests conceptual and practical avenues for future research, aiming perhaps to bring more order to the apparently multi-functional implication of the ventral midline thalamus in cognition.

Investigation of the influence of 45-minute pre-sleep social media use on sleep quality and memory consolidation in adolescents

Adolescents devote a significant portion of their time to smartphone usage, often engaging in social media activities. Social media use has previously been linked to diminished sleep quality and reduced sleep durations in correlational studies. In this experimental study, we aimed to investigate the influence of pre-sleep social media use on memory consolidation, subjective arousal and objectively assessed sleep quality in adolescents. We compared the social media condition to two reading conditions, one involving reading a book on a smartphone and the other reading from a physical book in a within-subjects design. Twenty participants between 12 and 14 years engaged in these activities for 45 min before bedtime. Contrary to our expectations, the results indicated that pre-sleep social media use did not have a discernible impact on sleep quality, pre-sleep arousal or memory consolidation. All assessed sleep measures remained consistent across the three conditions. Subjectively, the social media condition was rated less thrilling than the reading conditions. This suggests that, within the confines of this experiment, pre-sleep social media exposure did not significantly disrupt adolescents' sleep or their ability to consolidate memories during sleep. This deviation from previous correlational studies might be explained by a possible impact of mental health factors on media consumption and sleep or the fact that contrary to their daily routines participants had to sleep after our intervention and could not continue to engage in their activities. This highlights the need for further investigations into the complexities of this interaction.

What can the psychoneuroimmunology of yoga teach us about depression's psychopathology?

Depression, the most prevailing mental health condition, remains untreated in over 30% of patients. This cluster presents with sub-clinical inflammation. Investigations trialling anti-inflammatory medications had mixed results. The lack of results may result from inflammation's complexity and targeting only a few of depression's abnormal pathways. Mind-body therapies' biological and neuro-imaging studies offer valuable insights into depression psychopathology. Interestingly, mind-body therapies, like yoga, reverse the aberrant pathways in depression. These aberrant pathways include decreased cognitive function, interoception, neuroplasticity, salience and default mode networks connectivity, parasympathetic tone, increased hypothalamic-pituitary-adrenal (HPA) axis activity, and metabolic hyper/hypofunction. Abundant evidence found yogic techniques improving self-reported depressive symptoms across various populations. Yoga may be more effective in treating depression in conjunction with pharmacological and cognitive therapies. Yoga's psychoneuroimmunology teaches us that reducing allostatic load is crucial in improving depressive symptoms. Mind-body therapies promote parasympathetic tone, downregulate the HPA axis, reduce inflammation and boost immunity. The reduced inflammation promotes neuroplasticity and, subsequently, neurogenesis. Improving interoception resolves the metabolic needs prediction error and restores homeostasis. Additionally, by improving functional connectivity within the salience network, they restore the dynamic switching between the default mode and central executive networks, reducing rumination and mind-wandering. Future investigations should engineer therapies targeting the mechanisms mentioned above. The creation of multi-disciplinary health teams offering a combination of pharmacological, gene, neurofeedback, behavioural, mind-body and psychological therapies may treat treatment-resistant depression.

Postsynaptic competition between calcineurin and PKA regulates mammalian sleep-wake cycles

The phosphorylation of synaptic proteins is a significant biochemical reaction that controls the sleep-wake cycle in mammals1-3. Protein phosphorylation in vivo is reversibly regulated by kinases and phosphatases. In this study, we investigate a pair of kinases and phosphatases that reciprocally regulate sleep duration. First, we perform a comprehensive screen of protein kinase A (PKA) and phosphoprotein phosphatase (PPP) family genes by generating 40 gene knockout mouse lines using prenatal and postnatal CRISPR targeting. We identify a regulatory subunit of PKA (Prkar2b), a regulatory subunit of protein phosphatase 1 (PP1; Pppr1r9b) and catalytic and regulatory subunits of calcineurin (also known as PP2B) (Ppp3ca and Ppp3r1) as sleep control genes. Using adeno-associated virus (AAV)-mediated stimulation of PKA and PP1-calcineurin activities, we show that PKA is a wake-promoting kinase, whereas PP1 and calcineurin function as sleep-promoting phosphatases. The importance of these phosphatases in sleep regulation is supported by the marked changes in sleep duration associated with their increased and decreased activities, ranging from approximately 17.3 h per day (PP1 expression) to 4.3 h per day (postnatal CRISPR targeting of calcineurin). Localization signals to the excitatory post-synapse are necessary for these phosphatases to exert their sleep-promoting effects. Furthermore, the wake-promoting effect of PKA localized to the excitatory post-synapse negated the sleep-promoting effect of PP1-calcineurin. These findings indicate that PKA and PP1-calcineurin have competing functions in sleep regulation at excitatory post-synapses.

Comparative Analysis of Single-Channel and Multi-Channel Classification of Sleep Stages Across Four Different Data Sets

Background: Manually labeling sleep stages is time-consuming and labor-intensive, making automatic sleep staging methods crucial for practical sleep monitoring. While both single- and multi-channel data are commonly used in automatic sleep staging, limited research has adequately investigated the differences in their effectiveness. Methods: In this study, four public data sets-Sleep-SC, APPLES, SHHS1, and MrOS1-are utilized, and an advanced hybrid attention neural network composed of a multi-branch convolutional neural network and the multi-head attention mechanism is employed for automatic sleep staging. Results: The experimental results show that, for sleep staging using 2-5 classes, a combination of single-channel electroencephalography (EEG) and dual-channel electrooculography (EOG) consistently outperforms single-channel EEG with single-channel EOG, which in turn outperforms single-channel EEG or single-channel EOG alone. For instance, for five-class sleep staging using the MrOS1 data set, the combination of single-channel EEG and dual-channel EOG resulted in an accuracy of 87.18%, whereas the combination of single-channel EEG and single-channel EOG yielded an accuracy of 85.77%. In comparison, single-channel EEG alone achieved an accuracy of 85.25% and single-channel EOG alone achieved an accuracy of 83.66%. Conclusions: This study highlights the significance of combining EEG and EOG signals in automatic sleep staging, while also providing valuable insights for the channel design of portable sleep monitoring devices.

Associative Learning-Induced Synaptic Potentiation at the Two Major Hippocampal CA1 Inputs for Cued Memory Acquisition

Learning-associated functional plasticity at hippocampal synapses remains largely unexplored. Here, in a single session of reward-based trace conditioning, we examine learning-induced synaptic plasticity in the dorsal CA1 hippocampus (dCA1). Local field-potential recording combined with selective optogenetic inhibition first revealed an increase of dCA1 synaptic responses to the conditioned stimulus (CS) induced during conditioning at both Schaffer collaterals to the stratum radiatum (Rad) and temporoammonic input to the lacunosum moleculare (LMol). At these dCA1 inputs, synaptic potentiation of CS-responding excitatory synapses was further demonstrated by locally blocking NMDA receptors during conditioning and whole-cell recording sensory-evoked synaptic responses in dCA1 neurons from naive animals. An overall similar time course of the induction of synaptic potentiation was found in the Rad and LMol by multiple-site recording; this emerged later and saturated earlier than conditioned behavioral responses. Our experiments demonstrate a cued memory-associated dCA1 synaptic plasticity induced at both Schaffer collaterals and temporoammonic pathways.

Development of slow oscillation-spindle coupling from infancy to toddlerhood

Sleep has been demonstrated to support memory formation from early life on. The precise temporal coupling of slow oscillations (SOs) with spindles has been suggested as a mechanism facilitating this consolidation process in thalamocortical networks. Here, we investigated the development of sleep spindles and SOs and their coordinate interplay by comparing frontal, central, and parietal electroencephalogram recordings during a nap between infants aged 2-3 months (n = 31) and toddlers aged 14-17 months (n = 49). Spindles and SOs showed quite different maturational patterns between age groups, as to topography, amplitude, and density. Notably, spindle-SO co-occurrence in the infants did not exceed chance levels and was increased to significant levels only in the toddlers. In the infants, the slow SO upstate over frontocortical regions was even associated with a significant decrease in spindles, contrasting with the adult-like increase in spindles seen in toddlers. These results point to an immature processing in thalamocortical networks during sleep in early infancy, possibly diminishing the efficacy of sleep-dependent memory formation at this age.

Resting After Learning Facilitates Memory Consolidation and Reverses Spatial Reorientation Impairments in 'New Surroundings' in 3xTg-AD Mice

Sleep is an essential component of productive memory consolidation and waste clearance, including pathology associated with Alzheimer's disease (AD). Facilitation of sleep decreases Aβ and tau accumulation and is important for the consolidation of spatial memories. We previously found that 6-month female 3xTg-AD mice were impaired at spatial reorientation. Given the association between sleep and AD, we assessed the impact of added rest on impaired spatial reorientation that we previously observed. We randomly assigned 3xTg-AD mice to a rest (n=7; 50 min pre- & post-task induced rest) or a non-rest group (n=7; mice remained in the home cage pre- & post-task). Mice in both groups were compared to non-Tg, age-matched, non-rest controls (n=6). To confirm that our sleep condition induced sleep, we performed the same experiment with rest sessions for both 3xTg-AD and non-Tg mice (n=6/group) implanted with recording electrodes to capture local field potentials (LFPs), which were used to classify sleep states. Markers of pathology were also assessed in the parietal-hippocampal network, where we previously showed pTau positive cell density predicted spatial reorientation ability (pTau, 6E10, M78, and M22). However, we found that 3xTg-AD rest mice were not impaired at spatial reorientation compared to non-Tg mice and performed better than 3xTg-AD non-rest mice (replicating our previous work). This recovered behavior persisted despite no change in the density of pathology positive cells. Thus, improving sleep in early stages of AD pathology offers a promising approach for facilitating memory consolidation and improving cognition.

Closed-Loop Auditory Stimulation (CLAS) During Sleep Augments Language and Discovery Learning

Background/Objectives: Slow oscillation (SO) brainwaves observed during sleep have been shown to reflect the process of memory consolidation, that underlies the critical role of sleep in learning, memory, and other cognitive functions. Closed-loop auditory stimulation (CLAS) uses tones presented in phase with SOs to increase their amplitude and number, along with other brainwave signatures related to memory consolidation. Prior studies have found that CLAS maximizes the ability to perform rote memorization tasks, although this remains controversial. The present study examined whether CLAS affects a broader range of learning tasks than has been tested previously, including a rote language learning task requiring basic memorization and also two discovery learning tasks requiring insight, hypothesis testing, and integration of experience, all processes that benefit from memory consolidation. Methods: Twenty-eight healthy participants performed language and discovery learning tasks before sleeping in our laboratory for three continuous nights per week over two weeks, with verum or control CLAS using a prototype NeuroGevity system (NeuroGeneces, Inc., Santa Fe, NM, USA) in a crossed, randomized, double-blind manner. Results: Language learning showed a 35% better word recall (p = 0.048), and discovery learning showed a 26% better performance (p < 0.001) after three continuous nights of CLAS vs. control. EEG measures showed increased SO amplitude and entrainment, SO-spindle coupling, and other features that may underlie the learning benefits of CLAS. Conclusions: Taken together, the present results show that CLAS can alter brain dynamics and enhance learning, especially in complex discovery learning tasks that may benefit more from memory consolidation compared with rote word pair or language learning.

Sleep is necessary for experience-dependent sequence plasticity in mouse primary visual cortex

STUDY OBJECTIVES

Repeated exposure to familiar visual sequences drives experience-dependent and sequence-specific plasticity in mouse primary visual cortex (V1). Prior work demonstrated a critical role for sleep in consolidating a related but mechanistically distinct form of experience-dependent plasticity in V1. Here, we assessed the role of sleep in consolidation of spatiotemporal sequence learning (sequence plasticity) in mouse V1.

METHODS

Visually evoked potentials (VEPs) were recorded in awake, head-fixed mice viewing sequences of four visual stimuli. Each sequence was presented 200 times per session, across multiple sessions, to drive plasticity. The effects of sleep consolidation time and sleep deprivation on plasticity were assessed.

RESULTS

Sequence plasticity occurred in V1 following as little as one hour of ad libitum sleep and increased with longer periods of sleep. Sleep deprivation blocked sequence plasticity consolidation, which recovered following subsequent sleep.

CONCLUSIONS

Sleep is required for the consolidation of sequence plasticity in mouse V1.

Motor learning promotes regionally-specific spindle-slow wave coupled cerebral memory reactivation

Sleep is essential for the optimal consolidation of newly acquired memories. This study examines the neurophysiological processes underlying memory consolidation during sleep, via reactivation. Here, we investigated the impact of slow wave - spindle (SW-SP) coupling on regionally-task-specific brain reactivations following motor sequence learning. Utilizing simultaneous EEG-fMRI during sleep, our findings revealed that memory reactivation occured time-locked to coupled SW-SP complexes, and specifically in areas critical for motor sequence learning. Notably, these reactivations were confined to the hemisphere actively involved in learning the task. This regional specificity highlights a precise and targeted neural mechanism, underscoring the crucial role of SW-SP coupling. In addition, we observed double-dissociation whereby primary sensory areas were recruited time-locked to uncoupled spindles; suggesting a role for uncoupled spindles in sleep maintenance. These findings advance our understanding the functional significance of SW-SP coupling for enhancing memory in a regionally-specific manner, that is functionally dissociable from uncoupled spindles.

Brief sleep disruption alters synaptic structures among hippocampal and neocortical somatostatin-expressing interneurons

Study objectives

Brief sleep loss alters cognition and synaptic structures of principal neurons in hippocampus and neocortex. However, while in vivo recording and bioinformatic data suggest that inhibitory interneurons are more strongly affected by sleep loss, it is unclear how sleep and sleep deprivation affect interneurons' synapses. Disruption of the SST+ interneuron population seems to be a critical early sign of neuropathology in Alzheimer's dementia, schizophrenia, and bipolar disorder - and the risk of developing all three is increased by habitual sleep loss. We aimed to test how the synaptic structures of SST+ interneurons in various brain regions are affected by brief sleep disruption.

Methods

We used Brainbow 3.0 to label SST+ interneurons in the dorsal hippocampus, prefrontal cortex, and visual cortex of male SST-CRE transgenic mice, then compared synaptic structures in labeled neurons after a 6-h period of ad lib sleep, or gentle handling sleep deprivation (SD) starting at lights on.

Results

Dendritic spine density among SST+ interneurons in both hippocampus and neocortex was altered in a subregion-specific manner, with increased overall and thin spine density in CA1, dramatic increases in spine volume and surface area in CA3, and small but significant decreases in spine size in CA1, PFC and V1.

Conclusions

Our suggest that the synaptic connectivity of SST+ interneurons is significantly altered in a brain region-specific manner by a few hours of sleep loss. This suggests a cell type-specific mechanism by which sleep loss disrupts cognition and alters excitatory-inhibitory balance in brain networks.

Significance Statement

Changes to the function of somatostatin-expressing (SST+) interneurons have been implicated in the etiology of psychiatric and neurological disorders in which both cognition and sleep behavior are affected. Here, we measure the effects of very brief experimental sleep deprivation on synaptic structures of SST+ interneurons in hippocampus and neocortex, in brain structures critical for sleep-dependent memory processing. We find that only six hours of sleep deprivation restructures SST+ interneurons' dendritic spines, causing widespread and subregion-specific changes to spine density and spine size. These changes have the potential to dramatically alter excitatory-inhibitory balance across these brain networks, leading to cognitive disruptions commonly associated with sleep loss.

No effect of napping on episodic foresight and prospective memory in kindergarten children

Preschool children often have problems in remembering to carry out a planned behaviour. This study investigated the impact of napping on episodic foresight (planning for future events) and prospective memory (remembering to perform an action in the future) in 2-3-year-old children. In a quasi-experimental design, we compared children who napped (nap condition, n = 20) after receiving information about an upcoming problem (episodic foresight task) and a delayed intention (prospective memory task) with those who stayed awake (wake condition, n = 43). We hypothesised that napping would improve performance in the episodic foresight and the prospective memory tasks. Contrary to the hypothesis, napping did not significantly affect children's episodic foresight or prospective memory performance, even after controlling for the group difference in age. Task performance was primarily explained by memory effects and age. Further research that incorporates stricter controls and evaluates pre-nap memory strength is necessary fully to elucidate the complex interplay between napping, age, episodic foresight, and prospective memory performance in young children.

Difficulty in artificial word learning impacts targeted memory reactivation and its underlying neural signatures

Sleep associated memory consolidation and reactivation play an important role in language acquisition and learning of new words. However, it is unclear to what extent properties of word learning difficulty impact sleep associated memory reactivation. To address this gap, we investigated in 22 young healthy adults the effectiveness of auditory targeted memory reactivation (TMR) during non-rapid eye movement sleep of artificial words with easy and difficult to learn phonotactical properties. Here, we found that TMR of the easy words improved their overnight memory performance, whereas TMR of the difficult words had no effect. By comparing EEG activities after TMR presentations, we found an increase in slow wave density independent of word difficulty, whereas the spindle-band power nested during the slow wave up-states - as an assumed underlying activity of memory reactivation - was significantly higher in the easy/effective compared to the difficult/ineffective condition. Our findings indicate that word learning difficulty by phonotactics impacts the effectiveness of TMR and further emphasize the critical role of prior encoding depth in sleep associated memory reactivation.

The role of REM sleep in neural differentiation of memories in the hippocampus

When faced with a familiar situation, we can use memory to make predictions about what will happen next. If such predictions turn out to be erroneous, the brain can adapt by differentiating the representations of the cues that generated the prediction from the mispredicted item itself, reducing the likelihood of future prediction errors. Prior work by Kim et al. (2017) found that violating a sequential association in a statistical learning paradigm triggered differentiation of the neural representations of the associated items in the hippocampus. Here, we used fMRI to test the preregistered hypothesis that this hippocampal differentiation occurs only when violations are followed by rapid eye movement (REM) sleep. In the morning, participants first learned that some items predict others (e.g., A predicts B) then encountered a violation in which a predicted item (B) failed to appear when expected after its associated item (A); the predicted item later appeared on its own after an unrelated item. Participants were then randomly assigned to one of three conditions: remain awake, take a nap containing non-REM sleep only, or take a nap with both non-REM and REM sleep. While the predicted results were not observed in the preregistered left CA2/3/DG ROI, we did observe evidence for our hypothesis in closely related hippocampal ROIs, uncorrected for multiple comparisons: In right CA2/3/DG, differentiation in the group with REM sleep was greater than in the groups without REM sleep (wake and non-REM nap); this differentiation was item-specific and concentrated in right DG. Differentiation effects were also greater in bilateral DG when the predicted item was more strongly reactivated during the violation. Overall, the results presented here provide initial evidence linking REM sleep to changes in the hippocampal representations of memories in humans.

Goal Shifts Structure Memories and Prioritize Event-defining Information in Memory

Every day, we encounter far more information than we could possibly remember. Thus, our memory systems must organize and prioritize the details from an experience that can adaptively guide the storage and retrieval of specific episodic events. Prior work has shown that shifts in internal goal states can function as event boundaries, chunking experiences into distinct and memorable episodes. In addition, at short delays, memory for contextual information at boundaries has been shown to be enhanced compared with items within each event. However, it remains unclear if these memory enhancements are limited to features that signal a meaningful transition between events. To determine how changes in dynamic goal states influence the organization and content of long-term memory, we designed a 2-day experiment in which participants viewed a series of black-and-white objects surrounded by a color border on a two-by-two grid. The location of the object on the grid determined which of two tasks participants performed on a given trial. To examine if distinct types of goal shifts modulate the effects of event segmentation, we changed the border color, the task, or both after every four items in a sequence. We found that goal shifts influenced temporal memory in a manner consistent with the formation of distinct events. However, for subjective memory representations in particular, these effects differed by the type of event boundary. Furthermore, to examine if goal shifts lead to the prioritization of goal-relevant features in longer lasting memories, we tested source memory for each object's color and grid location both immediately and after a 24-hr delay. On the immediate test, boundaries enhanced the memory for all concurrent source features compared with nonboundary items, but only if those boundaries involved a goal shift. In contrast, after a delay, the source memory was selectively enhanced for the feature relevant to the goal shift. These findings suggest that goals can adaptively structure memories by prioritizing contextual features that define a unique episode in memory.

Association between sleep quality and cognitive impairment in older adults hypertensive patients in China: a case-control study

Background

Previous studies have found that poor sleep quality promotes the occurrence of cognitive impairment (CI), but this relationship has been rarely reported in older adults hypertensive patients. The purpose of this study was to investigate the relationship between sleep quality and CI in older adults hypertensive patients and the mediating effect of sleep quality between physical activity (PA) and CI.

Methods

A total of 2072 older adults hypertensive patients were included in this case-control study. Five hundred and eighteen older adults hypertensive patients with CI were matched 1:3 by age and sex to 1,554 older adults hypertensive patients with normal cognitive function. The International Physical Activity Questionnaire-Long Form, Pittsburgh Sleep Quality Index, and Mini-Mental State Examination were used to evaluate PA intensity, sleep quality, and cognitive function in older adults hypertensive patients. Multivariate logistic regression and the mediation package in R Language were used to analyze the relationship between sleep quality and CI and the mediating effect of sleep quality between PA intensity and CI in older adults hypertensive patients.

Results

After adjusting for all confounding factors, sleep quality was positively correlated with CI in older adults hypertensive patients (OR = 2.565, 95%CI: 1.958-3.360, p < 0.001), and this relationship also existed in the older adults hypertensive patients with education levels of primary school and below and junior high school and above (OR = 2.468, 95%CI: 1.754-3.473, p < 0.001; OR = 2.385, 95%CI: 1.367-4.161, p = 0.002). In addition, sleep quality mediated part of the mediating effect between PA intensity and CI in older adults hypertensive patients (Za*Zb: - 17.19339; 95%CI: -0.37312, -0.04194).

Conclusion

Poor sleep quality was associated with the occurrence of CI in older adults hypertensive patients, and this relationship also existed in older adults hypertensive patients with education levels of primary school and below and junior high school and above.

Can Neuromodulation Improve Sleep and Psychiatric Symptoms?

PURPOSE OF REVIEW

In this review, we evaluate recent studies that employ neuromodulation, in the form of non-invasive brain stimulation, to improve sleep in both healthy participants, and patients with psychiatric disorders. We review studies using transcranial electrical stimulation, transcranial magnetic stimulation, and closed-loop auditory stimulation, and consider both subjective and objective measures of sleep improvement.

RECENT FINDINGS

Neuromodulation can alter neuronal activity underlying sleep. However, few studies utilizing neuromodulation report improvements in objective measures of sleep. Enhancements in subjective measures of sleep quality are replicable, however, many studies conducted in this field suffer from methodological limitations, and the placebo effect is robust. Currently, evidence that neuromodulation can effectively enhance sleep is lacking. For the field to advance, methodological issues must be resolved, and the full range of objective measures of sleep architecture, alongside subjective measures of sleep quality, must be reported. Additionally, validation of effective modulation of neuronal activity should be done with neuroimaging.

Auditory processing up to cortex is maintained during sleep spindles

Sleep spindles are transient 11-16 Hz brain oscillations generated by thalamocortical circuits. Their role in memory consolidation is well established, but how they play a role in sleep continuity and protection of memory consolidation against interference is unclear. One theory posits that spindles or a neural refractory period following their offset act as a gating mechanism, blocking sensory information en route to the cortex at the level of the thalamus. An alternative model posits that spindles do not participate in the suppression of neural responses to sound, although they can be produced in response to sound. We present evidence from three experiments using electroencephalography and magnetoencephalography in humans that examine different evoked responses in the presence of and following sleep spindles. The results provide convergent empirical evidence suggesting that auditory processing up to cortex is maintained during sleep spindles, and their refractory periods.

Long-term memory formation for voices during sleep in three-month-old infants

The ability to form long-term memories begins in early infancy. However, little is known about the specific mechanisms that guide memory formation during this developmental stage. We demonstrate the emergence of a long-term memory for a novel voice in three-month-old infants using the EEG mismatch response (MMR) to the word "baby". In an oddball-paradigm, a frequent standard, and two rare deviant voices (novel and mother) were presented before (baseline), and after (test) familiarizing the infants with the novel voice and a subsequent nap. Only the mother deviant but not the novel deviant elicited a late frontal MMR (∼850 ms) at baseline, possibly reflecting a long-term memory representation for the mother's voice. Yet, MMRs to the novel and mother deviant significantly increased in similarity after voice familiarization and sleep. Moreover, both MMRs showed an additional early (∼250 ms) frontal negative component that is potentially related to deviance processing in short-term memory. Enhanced spindle activity during the nap predicted an increase in late MMR amplitude to the novel deviant and increased MMR similarity between novel and mother deviant. Our findings indicate that the late positive MMR in infants might reflect emergent long-term memory that benefits from sleep spindles.

Orexin Receptor Antagonists for the Prevention and Treatment of Alzheimer's Disease and Associated Sleep Disorders

Orexins/hypocretins are neuropeptides produced by the hypothalamic neurons, binding two G-protein coupled receptors (orexin 1 and orexin 2 receptors) and playing a critical role in regulating arousal, wakefulness, and various physiological functions. Given the high prevalence of sleep disturbances in Alzheimer's disease (AD) and their reported involvement in AD pathophysiology, the orexin system is hypothesized to contribute to the disease pathogenesis. Specifically, recent evidence suggests that orexin's influence may extend beyond sleep regulation, potentially affecting amyloid-β and tau pathologies. Dual orexin receptor antagonists (DORAs), namely suvorexant, lemborexant, and daridorexant, demonstrated efficacy in treating chronic insomnia disorder across diverse clinical populations. Considering their stabilizing effects on sleep parameters and emerging evidence of a possible neuroprotective role, these agents represent a promising strategy for AD management. This leading article reviews the potential use of orexin receptor antagonists in AD, particularly focusing on their effect in modulating disease-associated sleep disturbances and clinical outcomes. Overall, clinical studies support the use of DORAs to enhance sleep quality in patients with AD with comorbid sleep and circadian sleep-wake rhythm disorders. Preliminary results also suggest that these compounds might influence AD pathology, potentially affecting disease progression. Conversely, research on selective orexin receptor antagonists in AD is currently limited. Further investigation is needed to explore orexin antagonism not only as a symptomatic treatment for sleep disturbances, but also for its broader implications in modifying AD neurodegeneration, emphasizing mechanisms of action and long-term outcomes.

Neuroplasticity Meets Artificial Intelligence: A Hippocampus-Inspired Approach to the Stability-Plasticity Dilemma

The stability-plasticity dilemma remains a critical challenge in developing artificial intelligence (AI) systems capable of continuous learning. This perspective paper presents a novel approach by drawing inspiration from the mammalian hippocampus-cortex system. We elucidate how this biological system's ability to balance rapid learning with long-term memory retention can inspire novel AI architectures. Our analysis focuses on key mechanisms, including complementary learning systems and memory consolidation, with emphasis on recent discoveries about sharp-wave ripples and barrages of action potentials. We propose innovative AI designs incorporating dual learning rates, offline consolidation, and dynamic plasticity modulation. This interdisciplinary approach offers a framework for more adaptive AI systems while providing insights into biological learning. We present testable predictions and discuss potential implementations and implications of these biologically inspired principles. By bridging neuroscience and AI, our perspective aims to catalyze advancements in both fields, potentially revolutionizing AI capabilities while deepening our understanding of neural processes.

Binaural beats at 0.25 Hz shorten the latency to slow-wave sleep during daytime naps

Binaural beats can entrain neural oscillations and modulate behavioral states. However, the effect of binaural beats, particularly those with slow frequencies (< 1 Hz), on sleep remains poorly understood. We hypothesized that 0.25-Hz beats can entrain neural oscillations and enhance slow-wave sleep by shortening its latency or increasing its duration. To investigate this, we included 12 healthy participants (six women; mean age, 25.4 ± 2.6 years) who underwent four 90-min afternoon nap sessions, comprising a sham condition (without acoustic stimulation) and three binaural-beat conditions (0, 0.25, or 1 Hz) with a 250-Hz carrier tone. The acoustic stimuli, delivered through earphones, were sustained throughout the 90-min nap period. Both N2- and N3- latencies were shorter in the 0.25-Hz binaural beats condition than in the sham condition. We observed no significant results regarding neural entrainment at slow frequencies, such as 0.25 and 1 Hz, and the modulation of sleep oscillations, including delta and sigma activity, by binaural beats. In conclusion, this study demonstrated the potential of binaural beats at slow frequencies, specifically 0.25 Hz, for inducing slow-wave sleep in generally healthy populations.

Efficacy of non-invasive brain stimulation for post-stroke sleep disorders: a systematic review and meta-analysis

Objective

This study aimed to systematically assess the clinical efficacy of non-invasive brain stimulation (NIBS) for treating post-stroke sleep disorders (PSSD).

Methods

We conducted thorough literature search across multiple databases, including PubMed, Web of Science, EmBase, Cochrane Library, Scopus, China Biology Medicine (CBM); China National Knowledge Infrastructure (CNKI); Technology Periodical Database (VIP), and Wanfang Database, focusing on RCTs examining NIBS for PSSD. Meta-analyses were performed using RevMan 5.4 and Stata 14.

Results

Eighteen articles were reviewed, including 16 on repetitive Transcranial Magnetic Stimulation (rTMS), one on Theta Burst Stimulation (TBS), and two on transcranial Direct Current Stimulation (tDCS). Meta-analysis results indicated that rTMS within NIBS significantly improved the Pittsburgh Sleep Quality Index (PSQI) score (MD = -1.85, 95% CI [-2.99, -0.71], p < 0.05), the 17-item Hamilton Depression Rating Scale (HAMD-17) score [MD = -2.85, 95% CI (-3.40, -2.30), p < 0.05], and serum brain-derived neurotrophic factor (BDNF) levels [MD = 4.19, 95% CI (2.70, 5.69), p < 0.05], while reducing the incidence of adverse reactions [RR = 0.36, 95% CI (0.23, 0.55), p < 0.05]. TBS significantly improved the PSQI score in patients with PSSD (p < 0.05). Conversely, tDCS significantly improved the HAMD-17 score in PSSD patients [MD = -1.52, 95% CI (-3.41, -0.64), p < 0.05]. Additionally, rTMS improved sleep parameters, including Stage 2 sleep (S2%) and combined Stage 3 and 4 sleep (S3 + S4%) (p < 0.05), while tDCS improved total sleep time (TST) and sleep efficiency (SE) (p < 0.05).Subgroup analysis results indicated: (1) Both LF-rTMS and HF-rTMS improved PSQI scores (p < 0.05). (2) Both rTMS combined with medication and rTMS alone improved PSQI scores (p < 0.05). Compared to the sham/blank group, the rTMS group showed improvements in SE, sleep latency (SL), S1%, S3 + S4%, and REM sleep (REM%). The rTMS combined with medication group showed improved SL compared to the medication-only group (p < 0.05).

Conclusion

NIBS effectively improves sleep quality, structure, depression levels, and BDNF levels in PSSD patients, while also being safe. Further investigations into the potential of NIBS in PSSD treatment may provide valuable insights for clinical applications.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, CRD42023485317.