Auditory closed-loop stimulation of the sleep slow oscillation enhances memory

Overnight changes in performance fatigability and their relationship to modulated deep sleep oscillations via auditory stimulation

Deep sleep oscillations are proposed to be central in restoring brain function and to affect different aspects of motor performance such as facilitating the consolidation of motor sequences resulting in faster and more accurate sequence tapping. Yet, whether deep sleep modulates performance fatigability during fatiguing tasks remains unexplored. We investigated overnight changes in tapping speed and resistance against performance fatigability via a finger tapping task. During fast tapping, fatigability manifests as a reduction in speed (or "motor slowing") which affects all tapping tasks, including motor sequences used to study motor memory formation. We further tested whether overnight changes in performance fatigability are influenced by enhancing deep sleep oscillations using auditory stimulation. We found an overnight increase in tapping speed alongside a reduction in performance fatigability and perceived workload. Auditory stimulation led to a global enhancement of slow waves and both slow and fast spindles during the stimulation window and a local increase in slow spindles in motor areas across the night. However, overnight performance improvements were not significantly modulated by auditory stimulation and changes in tapping speed or performance fatigability were not predicted by individual changes in deep sleep oscillations. Our findings demonstrate overnight changes in fatigability but revealed no evidence suggesting that this effect is causally linked to temporary augmentation of slow waves or sleep spindles. Our results are important for future studies using tapping tasks to test the relationship between sleep and motor memory consolidation, as overnight changes in objectively measured and subjectively perceived fatigue likely impact behavioural outcomes.

Neuronal oscillations in cognition: Down syndrome as a model of mouse to human translation

Down syndrome (DS), a prevalent cognitive disorder resulting from trisomy of human chromosome 21 (Hsa21), poses a significant global health concern. Affecting approximately 1 in 800 live births worldwide, DS is the leading genetic cause of intellectual disability and a major predisposing factor for early-onset Alzheimer's dementia. The estimated global population of individuals with DS is 6 million, with increasing prevalence due to advances in DS health care. Global efforts are dedicated to unraveling the mechanisms behind the varied clinical outcomes in DS. Recent studies on DS mouse models reveal disrupted neuronal circuits, providing insights into DS pathologies. Yet, translating these findings to humans faces challenges due to limited systematic electrophysiological analyses directly comparing human and mouse. Additionally, disparities in experimental procedures between the two species pose hurdles to successful translation. This review provides a concise overview of neuronal oscillations in human and rodent cognition. Focusing on recent DS mouse model studies, we highlight disruptions in associated brain function. We discuss various electrophysiological paradigms and suggest avenues for exploring molecular dysfunctions contributing to DS-related cognitive impairments. Deciphering neuronal oscillation intricacies holds promise for targeted therapies to alleviate cognitive disabilities in DS individuals.

Efficacy and mechanisms of repeated closed-loop auditory exposure during slow-wave sleep for internet gaming disorder

Internet Gaming Disorder (IGD) is marked by impaired psychological and social functioning but remains without effective treatments. Cue exposure therapy (CET) is typically administered during wakefulness to help extinguish addictive memories. However, recent studies suggest that sleep may be an optimal state for memory modulation. This study aimed to assess the efficacy of repeated closed-loop exposure to game sounds during UP-state of slow-wave sleep (SWS) on IGD. 84 participants meeting DSM-5 criteria for IGD were randomly assigned to sleep intervention/control groups (SIG/SCG) or awake intervention/control groups (AIG/ACG) with two consecutive days of intervention. During SWS of two intervention nights, around 300 sounds were exposed at slow-wave UP-state. While the awake groups received similar auditory cue exposure during the awake state for two consecutive days. Cravings, playtime, and P300 amplitude in the cue reactivity task were recorded at baseline, post-intervention, and follow-up intervals (1, 2, 3, weeks, and 1 month). Results showed that the SIG significantly reduced cravings (p < 0.001), and playtime (p = 0.009) at post-intervention and follow-up, whereas awake CET showed no effect. The SIG exhibited higher low-frequency and early spindle power, along with lower late spindle power after sound exposure. Notably, the linear increase in sound-elicited late spindle power across the 20 intervention blocks over two experiment nights was positively correlated with reduced cravings post-intervention (r = 0.54, p = 0.015), especially among participants achieving a craving reduction greater than 30% after one month. Our findings suggest that closed-loop auditory exposure during SWS presents a promising, non-invasive intervention strategy for treating IGD, potentially exerting its effects by modulating late spindle power.

The Future of Non-Invasive Brain Stimulation in Sleep Medicine

Non-invasive brain stimulation (NIBS) methods carry particular appeal as non-pharmacological approaches to inducing or improving sleep. However, intense research efforts to use transcranial magnetic stimulation (TMS) and electrical stimulation (tES) for sleep modulation have not yet delivered evidence-based NIBS treatments in sleep medicine. The main obstacles lie in insufficiently robust stimulation protocols that affect neurophysiological and self-reported sleep parameters, inadequately controlled-and explained-placebo effects, and heterogeneity in patient populations and outcome parameters. Recent technological advances, e.g., transcranial ultrasound stimulation (TUS) and temporal interference stimulation (TIS), make deep brain structures feasible targets. Real-time approaches, e.g., closed-loop auditory stimulation (CLAS), demonstrate efficacious modulation of different sleep oscillations by tuning stimulation to ongoing brain activity. The identification of sleep-regulatory regions and cell types in the cerebral cortex and thalamus provides new specific targets. To turn this neuroscientific progress into therapeutic advancement, conceptual reframing is warranted. Chronic insomnia may not be optimally suited to demonstrate NIBS efficacy due to the mismatch between self-reported symptoms and polysomnographic sleep parameters. More feasible initial approaches could be to (1) modulate specific sleep oscillations to promote specific sleep functions, (2) modify nightmares and traumatic memories with targeted memory reactivation, (3) increase 'wake intensity' in patients with depression to improve daytime fatigue and elevate sleep pressure and (4) disrupt pathological activity in sleep-dependent epilepsies. Effective treatments in these areas of sleep medicine seem in reach but require rigorously designed clinical trials to identify which NIBS strategies bring real benefit in sleep medicine.

The structure of sleep and how it may be altered by visual impairments

Individuals with visual impairments often experience poor sleep health, which may impact brain physiology and function, as evidenced by altered brain activity during sleep. The sleeping brain can be categorized into stages: three non-rapid eye movement (NREM) stages and one rapid eye movement (REM) stage, with each stage defined by its structure, that is, the duration and frequency of specific brain oscillations. Research investigating alterations in sleep structure among visually impaired individuals has yielded mixed results: some studies indicate reduced or absent deep sleep (N3), others report longer REM latency (the time until the first REM epoch), while some suggest that circadian dysfunction may play a more significant role than visual impairment itself. Sleep is regulated by two processes: the homeostatic sleep drive, which accumulates during wakefulness and is relieved during sleep, and the circadian process, which describes the 24-hour sleep-wake cycle. The circadian process is particularly vulnerable to disruption by visual impairments, as damage to the retina can alter photic entrainment, the process by which light signals from the retina align the circadian sleep-wake cycle with the solar day. Visually impaired individuals often experience a drifting sleep-wake cycle that misaligns with the light-dark cycle, and during periods of misalignment, sleep quality may be particularly poor, especially REM sleep, which is largely under circadian control. Some causes of visual impairment, such as glaucoma, may be more susceptible to circadian dysfunction than others, as glaucoma affects cells in the retinal layer necessary for photic entrainment, which in turn may increase the risk of changes to sleep structure. Given that abnormal sleep structure is associated with long-term health consequences, including increased risks of depression, anxiety, and cognitive decline, it may contribute to the high prevalence of these issues found among the visually impaired population. Further research is needed to clarify the roles of the causes of visual impairments, circadian misalignment, and the impact on sleep structure. A better understanding of these relationships could help develop targeted interventions to improve sleep and enhance health outcomes for visually impaired individuals.

Targeting Sleep Physiology to Modulate Glymphatic Brain Clearance

Sleep has been postulated to play an important role in the removal of potentially neurotoxic molecules, such as amyloid-β, from the brain via the glymphatic system. Disturbed sleep, on the other hand, may contribute to the accumulation of neurotoxins in brain tissue, eventually leading to neuronal death. A bidirectional relationship has been proposed between impaired sleep and neurodegenerative processes, which start years before the onset of clinical symptoms associated with conditions like Alzheimer's and Parkinson's diseases. Given the heavy burden these conditions place on society, it is imperative to develop interventions that promote efficient brain clearance, thereby potentially aiding in the prevention or slowing of neurodegeneration. In this review, we explore whether the metabolic clearance function of sleep can be enhanced through sensory (e.g., auditory, vestibular) or transcranial (e.g., magnetic, ultrasound, infrared light) stimulation, as well as pharmacological (e.g., antiepileptics) and behavioral (e.g., sleeping position, physical exercise, cognitive intervention) modulation of sleep physiology. A particular focus is placed on strategies to enhance slow-wave activity during nonrapid eye movement sleep as a driver of glymphatic brain clearance. Overall, this review provides a comprehensive overview on the potential preventative and therapeutic applications of sleep interventions in combating neurodegeneration, cognitive decline, and dementia.

Interictal network dysfunction and cognitive impairment in epilepsy

Epilepsy is diagnosed when neural networks become capable of generating excessive or hypersynchronous activity patterns that result in observable seizures. In many cases, epilepsy is associated with cognitive comorbidities that persist between seizures and negatively impact quality of life. Dysregulation of the coordinated physiological network interactions that are required for cognitive function has been implicated in mediating these enduring symptoms, but the causal mechanisms are often elusive. Here, we provide an overview of neural network abnormalities with the potential to contribute to cognitive dysfunction in epilepsy. We examine these pathological interactions across spatial and temporal scales, additionally highlighting the dynamics that arise in response to the brain's intrinsic capacity for plasticity. Understanding these processes will facilitate development of network-level interventions to address cognitive comorbidities that remain undertreated by currently available epilepsy therapeutics.

The Interplay Between the Sleep Slow Oscillation and Cerebrospinal Fluid: New Vistas for Insomnia Research

Insomnia disorder affects about 10% of the global population, representing a major health concern. Despite the availability of evidence-based treatments, the neurobiological mechanisms underpinning this disorder remain poorly understood. Recently, the investigation of the less than 1 Hz oscillations (commonly termed slow oscillations), a hallmark of slow wave sleep, has gained increased interest in research on insomnia. In this context, an intriguing perspective arises from the association between slow oscillations and metabolic waste clearance, an impaired process in individuals suffering from insomnia disorder. Indeed, the exploration of the relationships between cerebrospinal fluid dynamics and glymphatic system functions, which relate to brain metabolic clearance, and sleep slow oscillations may represent a promising avenue for future research in this field. This narrative review examines current knowledge about the intricate interplay among these mechanisms and their implications for insomnia disorder. Particular attention is given to the role of sleep slow oscillations in the clearance of metabolic waste during sleep, their coupling with cerebrospinal fluid oscillations, and the regulatory mechanisms underlying glymphatic function. The review emphasises the relevance of investigating sleep slow oscillations-related mechanisms in insomnia, intending to provide novel insights into the neurophysiological underpinnings of the disorder and contribute to more accurate diagnostic approaches. Furthermore, a deeper understanding of these mechanisms could pave the way for the development of innovative or adjunctive therapeutic strategies targeting sleep slow oscillations-related alterations in insomnia disorder.

Novel murine closed-loop auditory stimulation paradigm elicits macrostructural sleep benefits in neurodegeneration

Boosting slow-wave activity (SWA) by modulating slow waves through closed-loop auditory stimulation (CLAS) might provide a powerful non-pharmacological tool to investigate the link between sleep and neurodegeneration. Here, we established mouse CLAS (mCLAS)-mediated SWA enhancement and explored its effects on sleep deficits in neurodegeneration, by targeting the up-phase of slow waves in mouse models of Alzheimer's disease (AD, Tg2576) and Parkinson's disease (PD, M83). We found that tracking a 2 Hz component of slow waves leads to highest precision of non-rapid eye movement (NREM) sleep detection in mice, and that its combination with a 30° up-phase target produces a significant 15-30% SWA increase from baseline in wild-type (WTAD) and transgenic (TGAD) mice versus a mock stimulation group. Conversely, combining 2 Hz with a 40° phase target yields a significant increase ranging 30-35% in WTPD and TGPD mice. Interestingly, these phase-target-triggered SWA increases are not genotype dependent but strain specific. Sleep alterations that may contribute to disease progression and burden were described in AD and PD lines. Notably, pathological sleep traits were rescued by mCLAS, which elicited a 14% decrease of pathologically heightened NREM sleep fragmentation in TGAD mice, accompanied by a steep decrease in microarousal events during both light and dark periods. Overall, our results indicate that model-tailored phase targeting is key to modulate SWA through mCLAS, prompting the acute alleviation of key neurodegeneration-associated sleep phenotypes and potentiating sleep regulation and consolidation. Further experiments assessing the long-term effect of mCLAS in neurodegeneration may majorly impact the establishment of sleep-based therapies.

Sleep and cardiac autonomic modulation in older adults: Insights from an at-home study with auditory deep sleep stimulation

The autonomic nervous system regulates cardiovascular activity during sleep, likely impacting cardiovascular health. Aging, a primary cardiovascular risk factor, is associated with cardiac autonomic disbalance and diminished sleep slow waves. Therefore, slow waves may be linked to aging, autonomic activity and cardiovascular health. However, it is unclear how sleep and slow waves are linked to cardiac autonomic profiles across multiple nights in older adults. We conducted a randomized, crossover trial involving healthy adults aged 62-78 years. Across 2 weeks, we applied auditory stimulation to enhance slow waves and compared it with a SHAM period. We measured sleep parameters using polysomnography and derived heart rate, heart rate variability approximating parasympathetic activity, and blood pulse wave approximating sympathetic activity from a wearable. Here, we report the results of 14 out of 33 enrolled participants, and show that heart rate, heart rate variability and blood pulse wave within sleep stages differ between the first and second half of sleep. Furthermore, baseline slow-wave activity was related to cardiac autonomic activity profiles during sleep. Moreover, we found auditory stimulation to reduce heart rate variability, while heart rate and blood pulse wave remained unchanged. Lastly, within subjects, higher heart rate coincided with increased slow-wave activity, indicating enhanced autonomic activation when slow waves are pronounced. Our study shows the potential of cardiac autonomic markers to offer insights into participants' baseline slow-wave activity when recorded over multiple nights. Furthermore, we highlight that averaging cardiac autonomic parameters across a night may potentially mask dynamic effects of auditory stimulation, potentially playing a role in maintaining a healthy cardiovascular system.

Unraveling the neurophysiological correlates of phase-specific enhancement of motor memory consolidation via slow-wave closed-loop targeted memory reactivation

Memory consolidation can be enhanced during sleep using targeted memory reactivation (TMR) and closed-loop (CL) acoustic stimulation on the up-phase of slow oscillations (SOs). Here, we test whether applying TMR at specific phases of the SOs (up vs. down vs. no reactivation) can influence the behavioral and neural correlates of motor memory consolidation in healthy young adults. Results show that up- (as compared to down-) state cueing results in greater performance improvement. Sleep electrophysiological data indicate that up- (as compared to down-) stimulated SOs exhibits higher amplitude and greater peak-nested sigma power. Task-related functional magnetic resonance images reveal that up-state cueing strengthens activity in - and segregation of - striato-motor and hippocampal networks; and that these modulations are related to the beneficial effect of TMR on sleep features and performance. Overall, these findings highlight the potential of CL-TMR to induce phase-specific modulations of motor performance, sleep oscillations and brain responses during motor memory consolidation.

The effect of fasting on human memory consolidation

The consolidation of long-term memory is thought to critically rely on sleep. However, first evidence from a study in Drosophila suggests that hunger, as another brain state, can benefit memory consolidation as well. Here, we report two human (within-subjects crossover) experiments examining the effects of fasting (versus satiated conditions) during a 10-hour post-encoding consolidation period on subsequent recall of declarative and procedural memories in healthy men. In Experiment 1, participants (n = 16), after an 18.5-hour fasting period, encoded 3 memory tasks (word paired associates, a visual version of the Deese-Roediger-McDermott task, finger tapping) and subsequently either continued to fast or received standardized meals. Recall was tested 48 h later in a satiated state. Experiment 2 (n = 16 participants) differed from Experiment 1 in that a What-Where-When episodic memory task replaced the Deese-Roediger-McDermott task and recall was tested only 24 h later in a fasted state. Compared with the satiated state, fasting enhanced cued recall of word paired associates (more correct and faster responses) and item recognition in the What-Where-When task. By contrast, fasting impaired recall of episodic context memory, i.e., spatial context in the Deese-Roediger-McDermott task, and temporal-spatial context in the What-Where-When task. Procedural memory (finger tapping) remained unaffected. This pattern suggests a differential effect of fasting selectively promoting consolidation of semantic-like representations in cortical networks whereas hippocampal representations of episodic context are weakened. We speculate that hunger strengthens cortical representations by suppressing hippocampal interference during wake consolidation. Yet, the underlying mechanism remains to be clarified.

Emerging Technologies to Track and Improve Sleep Health

This review explores cutting-edge advancements, including wearable sleep trackers, brain age assessments, transcranial electrical stimulation (TES), acoustic stimulation, and glymphatic system modulation. Sleep trackers provide continuous monitoring of sleep patterns, while brain age estimation offers insights into brain health and early detection of accelerated aging. TES shows promise in improving mood, memory, and sleep. Acoustic stimulation during slow-wave sleep has been demonstrated to enhance memory consolidation. Additionally, optimizing the glymphatic system may facilitate brain waste clearance, crucial in preventing neurodegenerative diseases like Alzheimer's. However, significant challenges remain, including the need for rigorous longitudinal studies to validate these technologies' efficacy and safety.

Pupil size reveals arousal level fluctuations in human sleep

Recent animal research has revealed the intricate dynamics of arousal levels that are important for maintaining proper sleep resilience and memory consolidation. In humans, changes in arousal level are believed to be a determining characteristic of healthy and pathological sleep but tracking arousal level fluctuations has been methodologically challenging. Here we measured pupil size, an established indicator of arousal levels, by safely taping the right eye open during overnight sleep and tested whether pupil size affects cortical response to auditory stimulation. We show that pupil size dynamics change as a function of important sleep events across different temporal scales. In particular, our results show pupil size to be inversely related to the occurrence of sleep spindle clusters, a marker of sleep resilience. Additionally, we found pupil size prior to auditory stimulation to influence the evoked response, most notably in delta power, a marker of several restorative and regenerative functions of sleep. Recording pupil size dynamics provides insights into the interplay between arousal levels and sleep oscillations.

Low-Frequency Deep Brain Stimulation in Non-Rapid Eye Movement Sleep Modifies Memory Retention in Parkinson's Disease

BACKGROUND AND OBJECTIVE

Memory impairment is a frequent and debilitating symptom in neurodegenerative disorders. The objective of this study was to provide proof-of-principle that deep brain stimulation during sleep can modify memory consolidation in people with Parkinson's disease depending on the stimulation frequency that is applied.

METHODS

Twenty-four patients with Parkinson's disease who were treated with deep brain stimulation of the subthalamic nucleus were included in this single-blind pilot study. Six patients had to be excluded because of insomnia on the night of testing. Patients were randomized (1:1 ratio) to receiving either low frequency deep brain stimulation (4 Hz) or clinically used high frequency deep brain stimulation (130 Hz) during early non-rapid eye movement (NREM) sleep. The main outcome measure was overnight memory retention as measured by a validated declarative memory task.

RESULTS

Patients receiving low frequency deep brain stimulation during early NREM sleep (n = 9, 4 females, mean age 61.1 ± 4.3 years) showed improved overnight memory retention (z = 2.549, P = 0.011). Patients receiving clinically used high frequency deep brain stimulation (n = 9, 2 females, mean age 62.2 ± 7.1) did not show any improvement (z = 1.023, P = 0.306) leading to a significant difference between groups (z = 2.214, P = 0.027). Stronger improvement in memory function was correlated with increased cortical low frequency activity after low frequency deep brain stimulation as measured by electroencephalography (ρ = 0.711, P = 0.037).

CONCLUSION

These results provide proof-of-principle that memory can be modulated by frequency-specific deep brain stimulation during sleep. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

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.

Association of Sleep Spindle Rate With Memory Consolidation in Children With Rolandic Epilepsy

BACKGROUND AND OBJECTIVES

Rolandic epilepsy (RE), the most common childhood focal epilepsy syndrome, is characterized by a transient period of sleep-activated epileptiform activity in the centrotemporal regions and variable cognitive deficits. Sleep spindles are prominent thalamocortical brain oscillations during sleep that have been mechanistically linked to sleep-dependent memory consolidation in animal models and healthy controls. Sleep spindles are decreased in RE and related sleep-activated epileptic encephalopathies. To further evaluate the association between this electrographic biomarker and cognitive dysfunction in this common disease, we investigate whether children with RE have deficient sleep-dependent memory consolidation and whether impaired memory consolidation is associated with reduced sleep spindles in the centrotemporal regions.

METHODS

In this prospective case-control study, children were trained and tested on a validated probe of memory consolidation, the motor sequence task (MST). Sleep spindles were measured from high-density EEG during a 90-minute nap opportunity between MST training and testing using an automated sleep spindle detector validated for use in children with and without epilepsy.

RESULTS

Twenty-three children with RE (9 with active disease, 5F, age 6.9-12.8 years; 14 with resolved disease, 8F, age 8.8-17.8 years) and 19 age-matched and sex-matched controls (8F, age 6.9-18.7 years) were enrolled. Children with active epilepsy had decreased memory consolidation compared with control children (p = 0.001, mean percentage reduction 25.7%, 95% CI 10.3%-41.2%) and compared with children with resolved epilepsy (p = 0.007, mean percentage reduction 21.9%, 95% CI 6.2%-37.6%). Children with active epilepsy had decreased sleep spindle rates in the centrotemporal region compared with controls (p = 0.008, mean decrease 2.5 spindles per minute, 95% CI 0.7-4.4 spindles per minute). Spindle rate, but not spike rate or spike-wave index, correlated with sleep-dependent memory consolidation (p = 0.004, mean MST improvement of 3.9%, 95% CI 1.3%-6.4%, for each unit increase in spindles per minute).

DISCUSSION

Children with RE have impaired sleep-dependent memory consolidation during the active period of disease that correlates with a deficit in the sleep spindle rate. This finding identifies a noninvasive biomarker to aid diagnosis and a potential etiologic mechanism to guide therapeutic discovery of cognitive dysfunction in RE and related sleep-activated epilepsy syndromes.

EEG Abnormalities and Phenotypic Correlates in Preschoolers with Autism Spectrum Disorder: A Single-Center Study

Background: The literature suggests the existence of an association between autism spectrum disorders (ASDs) and subclinical electroencephalographic abnormalities (SEAs), which show a heterogeneous prevalence rate (12.5-60.7%) within the pediatric ASD population. The aim of this study was to investigate the EEG findings in a cohort of ASD preschoolers and their correlation with the phenotypic characteristics. Methods: We retrospectively reviewed data on 141 ASD preschoolers evaluated in a tertiary care university hospital over the period 2008-2018. All participants underwent at least one standard polygraphic electroencephalogram (EEG) and a clinical multidisciplinary assessment with standardized instruments. Results: 77 patients (55%) showed SEAs, which were mainly represented by epileptiform discharges (p < 0.00001), especially focal and multifocal (p = 0.010). Abnormal EEG (p = 0.035) and epileptiform discharges (p = 0.014) were associated with seizure onset and were predominant in sleep (p < 0.00001). Patients with abnormal tracing (p = 0.031) and slow abnormalities (p < 0.001) were significantly younger. ASD severity was not found to be correlated with EEG results, which showed a potential, albeit non-significant, association with some psychometric parameters. Very similar results were found when patients were divided according to sex. Conclusions: EEG abnormalities appear to correlate more with ASD internalizing, externalizing and emotional comorbidities, rather than with ASD core symptoms; larger samples are needed to further investigate this association.

Waste clearance shapes aging brain health

Brain health is intimately connected to fluid flow dynamics that cleanse the brain of potentially harmful waste material. This system is regulated by vascular dynamics, the maintenance of perivascular spaces, neural activity during sleep, and lymphatic drainage in the meningeal layers. However, aging can impinge on each of these layers of regulation, leading to impaired brain cleansing and the emergence of various age-associated neurological disorders, including Alzheimer's and Parkinson's diseases. Understanding the intricacies of fluid flow regulation in the brain and how this becomes altered with age could reveal new targets and therapeutic strategies to tackle age-associated neurological decline.

Pharmacological enhancement of slow-wave activity at an early disease stage improves cognition and reduces amyloid pathology in a mouse model of Alzheimer's disease

Introduction

Improving sleep in murine Alzheimer's disease (AD) is associated with reduced brain amyloidosis. However, the window of opportunity for successful sleep-targeted interventions, regarding the reduction in pathological hallmarks and related cognitive performance, remains poorly characterized.

Methods

Here, we enhanced slow-wave activity (SWA) during sleep via sodium oxybate (SO) oral administration for 2 weeks at early (6 months old) or moderately late (11 months old) disease stages in Tg2576 mice and evaluated resulting neuropathology and behavioral performance.

Results

We observed that the cognitive performance of 6-month-old Tg2576 mice significantly improved upon SO treatment, whereas no change was observed in 11-month-old mice. Histochemical assessment of amyloid plaques demonstrated that SO-treated 11-month-old Tg2576 mice had significantly less plaque burden than placebo-treated ones, whereas ELISA of insoluble protein fractions from brains of 6-month-old Tg2576 mice indicated lower Aβ-42/Aβ-40 ratio in SO-treated group vs. placebo-treated controls.

Discussion

Altogether, our results suggest that SWA-dependent reduction in brain amyloidosis leads to alleviated behavioral impairment in Tg2576 mice only if administered early in the disease course, potentially highlighting the key importance of early sleep-based interventions in clinical cohorts.

Multi-region processing during sleep for memory and cognition

Over the past decades, the understanding of sleep has evolved to be a fundamental physiological mechanism integral to the processing of different types of memory rather than just being a passive brain state. The cyclic sleep substates, namely, rapid eye movement (REM) sleep and non-REM (NREM) sleep, exhibit distinct yet complementary oscillatory patterns that form inter-regional networks between different brain regions crucial to learning, memory consolidation, and memory retrieval. Technical advancements in imaging and manipulation approaches have provided deeper understanding of memory formation processes on multi-scales including brain-wide, synaptic, and molecular levels. The present review provides a short background and outlines the current state of research and future perspectives in understanding the role of sleep and its substates in memory processing from both humans and rodents, with a focus on cross-regional brain communication, oscillation coupling, offline reactivations, and engram studies. Moreover, we briefly discuss how sleep contributes to other higher-order cognitive functions.

Acoustic Stimulation to Improve Slow-Wave Sleep in Alzheimer's Disease: A Multiple Night At-Home Intervention

OBJECTIVES

To investigate the efficacy of closed-loop acoustic stimulation (CLAS) during slow-wave sleep (SWS) to enhance slow-wave activity (SWA) and SWS in patients with Alzheimer's disease (AD) across multiple nights and to explore associations between stimulation, participant characteristics, and individuals' SWS response.

DESIGN

A 2-week, open-label at-home intervention study utilizing the DREEM2 headband to record sleep data and administer CLAS during SWS.

SETTING AND PARTICIPANTS

Fifteen older patients with AD (6 women, mean age: 76.27 [SD = 6.06], mean MOCA-score: 16.07 [SD = 6.94]), living at home with their partner, completed the trial.

INTERVENTION

Patients first wore the device for two baseline nights, followed by 14 nights during which the device was programmed to randomly either deliver acoustic stimulations of 50 ms pink noise (± 40 dB) targeted to the slow-wave up-phase during SWS or only mark the wave (sham).

RESULTS

On a group level, stimulation significantly enhanced SWA and SWS with consistent SWS enhancement throughout the intervention. However, substantial variability existed in individual responses to stimulation. Individuals received more stimulations on nights with increased SWS compared to baseline than on nights with no change or a decrease. In individuals, having lower baseline SWS correlated with receiving fewer stimulations on average during the intervention.

CONCLUSION

CLAS during SWS is a promising nonpharmacological method to enhance SWA and SWS in AD. However, patients with lower baseline SWS received fewer stimulations during the intervention, possibly resulting in less SWS enhancement. Individual variability in response to stimulation underscores the need to address personalized stimulation parameters in future research and therapy development.

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.

Physiological Entrainment: A Key Mind-Body Mechanism for Cognitive, Motor and Affective Functioning, and Well-Being

BACKGROUND

The human sensorimotor system can naturally synchronize with environmental rhythms, such as light pulses or sound beats. Several studies showed that different styles and tempos of music, or other rhythmic stimuli, have an impact on physiological rhythms, including electrocortical brain activity, heart rate, and motor coordination. Such synchronization, also known as the "entrainment effect", has been identified as a crucial mechanism impacting cognitive, motor, and affective functioning.

OBJECTIVES

This review examines theoretical and empirical contributions to the literature on entrainment, with a particular focus on the physiological mechanisms underlying this phenomenon and its role in cognitive, motor, and affective functions. We also address the inconsistent terminology used in the literature and evaluate the range of measurement approaches used to assess entrainment phenomena. Finally, we propose a definition of "physiological entrainment" that emphasizes its role as a fundamental mechanism that encompasses rhythmic interactions between the body and its environment, to support information processing across bodily systems and to sustain adaptive motor responses.

METHODS

We reviewed the recent literature through the lens of the "embodied cognition" framework, offering a unified perspective on the phenomenon of physiological entrainment.

RESULTS

Evidence from the current literature suggests that physiological entrainment produces measurable effects, especially on neural oscillations, heart rate variability, and motor synchronization. Eventually, such physiological changes can impact cognitive processing, affective functioning, and motor coordination.

CONCLUSIONS

Physiological entrainment emerges as a fundamental mechanism underlying the mind-body connection. Entrainment-based interventions may be used to promote well-being by enhancing cognitive, motor, and affective functions, suggesting potential rehabilitative approaches to enhancing mental health.

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.

Closed-loop auditory stimulation targeting alpha and theta oscillations during rapid eye movement sleep induces phase-dependent power and frequency changes

STUDY OBJECTIVES

Alpha and theta oscillations characterize the waking human electroencephalogram (EEG) and can be modulated by closed-loop auditory stimulation (CLAS). These oscillations also occur during rapid eye movement (REM) sleep, but their function here remains elusive. CLAS represents a promising tool to pinpoint how these brain oscillations contribute to brain function in humans. Here we investigate whether CLAS can modulate alpha and theta oscillations during REM sleep in a phase-dependent manner.

METHODS

We recorded high-density EEG during an extended overnight sleep period in 18 healthy young adults. Auditory stimulation was delivered during both phasic and tonic REM sleep in alternating 6-second ON and 6-second OFF windows. During the ON windows, stimuli were phase-locked to four orthogonal phases of ongoing alpha or theta oscillations detected in a frontal electrode.

RESULTS

The phases of ongoing alpha and theta oscillations were targeted with high accuracy during REM sleep. Alpha and theta CLAS induced phase-dependent changes in power and frequency at the target location. Frequency-specific effects were observed for alpha trough (speeding up) and rising (slowing down) and theta trough (speeding up) conditions. CLAS-induced phase-dependent changes were observed during both REM sleep substages, even though auditory evoked potentials were very much reduced in phasic compared to tonic REM sleep.

CONCLUSIONS

This study provides evidence that faster REM sleep rhythms can be modulated by CLAS in a phase-dependent manner. This offers a new approach to investigating how modulation of REM sleep oscillations affects the contribution of this vigilance state to brain function.

Does fragmented sleep mediate the relationship between deficits in sleep spindles and memory consolidation in schizophrenia?

Study Objectives

Sleep spindles, defining electroencephalographic oscillations of nonrapid eye movement (NREM) stage 2 sleep (N2), mediate sleep-dependent memory consolidation (SDMC). Spindles are also thought to protect sleep continuity by suppressing thalamocortical sensory relay. Schizophrenia is characterized by spindle deficits and a correlated reduction of SDMC. We investigated whether this relationship is mediated by sleep fragmentation.

Methods

We detected spindles (12-15 Hz) during N2 at central electrodes in overnight polysomnography records from 56 participants with chronic schizophrenia and 59 healthy controls. Our primary measures of sleep continuity were the sleep fragmentation index and, in a subset of the data, visually scored arousals. SDMC was measured as overnight improvement on the finger-tapping motor sequence task.

Results

Participants with schizophrenia showed reductions of both spindle density (#/min) and SDMC in the context of normal sleep continuity and architecture. Spindle density predicted SDMC in both groups. In contrast, neither increased sleep fragmentation nor arousals predicted lower spindle density or worse SDMC in either group.

Conclusions

Our findings fail to support the hypothesis that sleep fragmentation accounts for spindle deficits, impaired SDMC, or their relationship in individuals with chronic schizophrenia. Instead, our findings are consistent with the hypothesis that spindle deficits directly impair memory consolidation in schizophrenia. Since sleep continuity and architecture are intact in this population, research aimed at developing interventions should instead focus on understanding dysfunction within the thalamocortical-hippocampal circuitry that both generates spindles and synchronizes them with other NREM oscillations to mediate SDMC.

Does sleep help children to generalise features like adults?

Children and adults have been shown to benefit from sleep with regard to the consolidation of declarative memories. Especially during childhood, the generalisation of information from social and non-social contexts is important for adaptable behaviour in new situations and might show specific features in children. Here, we investigated whether adults (n = 18) and children (n = 19) differ in their generalisation of features assessed in wake and sleep conditions. In a social paradigm, certain face features were associated with different types of offers (fair, unfair, friendly). While children tended to better recognise these faces, adults were better than children at associating the type of offer to unknown faces sharing these features with the previously encoded faces in the sleep condition. To assess generalisation of features in a non-social context, a probabilistic evaluative conditioning paradigm was used, where stimuli were associated with positive or negative values. We found no difference between children and adults or between the sleep and wake condition in the change in evaluation of the conditioned stimuli when paired congruently with a predefined value (positive/negative). Together, our results suggest a differential feature generalisation from mainly social contexts in children compared with adults.

Closed-loop auditory stimulation of slow-wave sleep in chronic insomnia: a pilot study

Insomnia is a prevalent and disabling condition whose treatment is not always effective. This pilot study explores the feasibility and effects of closed-loop auditory stimulation (CLAS) as a potential non-invasive intervention to improve sleep, its subjective quality, and memory consolidation in patients with insomnia. A total of 27 patients with chronic insomnia underwent a crossover, sham-controlled study with 2 nights of either CLAS or sham stimulation. Polysomnography was used to record sleep parameters, while questionnaires and a word-pair memory task were administered to assess subjective sleep quality and memory consolidation. The initial analyses included 17 patients who completed the study, met the inclusion criteria, and received CLAS. From those, 10 (58%) received only a small number of stimuli. In the remaining seven (41%) patients with sufficient CLAS, we evaluated the acute and whole-night effect on sleep. CLAS led to a significant immediate increase in slow oscillation (0.5-1 Hz) amplitude and activity, and reduced delta (1-4 Hz) and sigma/sleep spindle (12-15 Hz) activity during slow-wave sleep across the whole night. All these fundamental sleep rhythms are implicated in sleep-dependent memory consolidation. Yet, CLAS did not change sleep-dependent memory consolidation or sleep macrostructure characteristics, number of arousals, or subjective perception of sleep quality. Results showed CLAS to be feasible in patients with insomnia. However, a high variance in the efficacy of our automated stimulation approach suggests that further research is needed to optimise stimulation protocols to better unlock potential CLAS benefits for sleep structure and subjective sleep quality in such clinical settings.

Multi-night acoustic stimulation is associated with better sleep, amyloid dynamics, and memory in older adults with cognitive impairment

Sleep is a potential early, modifiable risk factor for cognitive decline and dementia. Impaired slow wave sleep (SWS) is pronounced in individuals with cognitive impairment (CI). Cognitive decline and impairments of SWS are bi-directionally linked in a vicious cycle. SWS can be enhanced non-invasively using phase-locked acoustic stimulation (PLAS), potentially breaking this vicious cycle. Eighteen healthy older adults (HC, agemean±sd, 68.3 ± 5.1) and 16 older adults (agemean±sd, 71.9 ± 3.9) with CI (Montreal Cognitive Assessment ≤ 25) underwent one baseline (sham-PLAS) night and three consecutive stimulation nights (real-PLAS). EEG responses and blood-plasma amyloid beta Aβ42/Aβ40 ratio were measured pre- and post-intervention, as was episodic memory. The latter was again evaluated 1 week and 3 months after the intervention. In both groups, PLAS induced a significant electrophysiological response in both voltage- and time-frequency analyses, and memory performance improved in association with the magnitude of this response. In the CI group, both electrophysiological and associated memory effects were delayed compared to the healthy group. After 3 intervention nights, electrophysiological response to PLAS was no longer different between CI and HC groups. Only in the CI sample, stronger electrophysiological responses were significantly associated with improving post-intervention Aβ42/Aβ40 ratios. PLAS seems to improve SWS electrophysiology, memory, and amyloid dynamics in older adults with CI. However, effects on memory require more time to unfold compared to healthy older adults. This indicates that PLAS may become a potential tool to ameliorate cognitive decline, but longer interventions are necessary to compensate for declining brain integrity. This study was pre-registered (clinicaltrials.gov: NCT04277104).

The effectiveness of exercise interventions targeting sleep in older adults with cognitive impairment or Alzheimer's disease and related dementias (AD/ADRD): A systematic review and meta-analysis

Sleep loss is associated with reduced health and quality of life, and increased risk of Alzheimer's disease and related dementias. Up to 66% of persons with Alzheimer's disease and related dementias experience poor sleep, which can predict or accelerate the progression of cognitive decline. Exercise is a widely accessible intervention for poor sleep that can protect against functional and cognitive decline. No previous systematic reviews have investigated the effectiveness of exercise for sleep in older adults with mild cognitive impairment or Alzheimer's disease and related dementias. We systematically reviewed controlled interventional studies of exercise targeting subjectively or objectively (polysomnography/actigraphy) assessed sleep in persons with mild cognitive impairment or Alzheimer's disease and related dementias. We conducted searches in PubMed, Embase, Scopus and Cochrane-Library (n = 6745). Nineteen randomised and one non-randomised controlled interventional trials were included, representing the experiences of 3278 persons with mild cognitive impairment or Alzheimer's disease and related dementias. Ten had low-risk, nine moderate-risk, and one high-risk of bias. Six studies with subjective and eight with objective sleep outcomes were meta-analysed (random-effects model). We found moderate- to high-quality evidence for the beneficial effects of exercise on self-reported and objectively-measured sleep outcomes in persons with mild cognitive impairment or Alzheimer's disease and related dementias. However, no studies examined key potential moderators of these effects, such as sex, napping or medication use. Our results have important implications for clinical practice. Sleep may be one of the most important modifiable risk factors for a range of health conditions, including cognitive decline and the progression of Alzheimer's disease and related dementias. Given our findings, clinicians may consider adding exercise as an effective intervention or adjuvant strategy for improving sleep in older persons with mild cognitive impairment or Alzheimer's disease and related dementias.

Brainwide hemodynamics predict neural rhythms across sleep and wakefulness in humans

The brain exhibits rich oscillatory dynamics that play critical roles in vigilance and cognition, such as the neural rhythms that define sleep. These rhythms continuously fluctuate, signaling major changes in vigilance, but the brainwide dynamics underlying these oscillations are unknown. Using simultaneous EEG and fast fMRI in humans drifting between sleep and wakefulness, we developed a machine learning approach to investigate which brainwide fMRI networks predict alpha (8-12 Hz) and delta (1-4 Hz) fluctuations. We predicted moment-to-moment EEG power variations from fMRI activity in held-out subjects, and found that information about alpha rhythms was highly separable in two networks linked to arousal and visual systems. Conversely, delta rhythms were diffusely represented on a large spatial scale across the cortex. These results identify the large-scale network patterns that underlie alpha and delta rhythms, and establish a novel framework for investigating multimodal, brainwide dynamics.

Sleep Architecture Changes in Diabetes

Data on the relationship between sleep architecture and diabetes are limited. However, some evidence suggests that slow-wave sleep (SWS) plays a crucial role in maintaining normal glucose homeostasis and influences insulin secretion capacity. Diabetes is often associated with reduced SWS, even in the absence of sleep-disordered breathing. Notably, selective suppression of SWS-without reducing total sleep time-can lead to significant increases in insulin resistance, decreased glucose tolerance, and a higher risk of diabetes. Given the growing interest in non-pharmacological lifestyle interventions, such as modifying sleep architecture, it is important to understand how sleep patterns differ in individuals with diabetes and whether these alterations impact diabetes risk and glycemic control. This review aims to provide a concise overview of the current findings on sleep architecture changes in people with diabetes.

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.

Selective Modulation of Fear Memory in Non-Rapid Eye Movement Sleep

Sleep stabilizes memories for their consolidation, but how to modify specific fear memory during sleep remains unclear. Here, it is reported that using targeted memory reactivation (TMR) to reactivate prior fear learning experience in non-slow wave sleep (NS) inhibits fear memory consolidation, while TMR during slow wave sleep (SWS) enhances fear memory in mice. Replaying conditioned stimulus (CS) during sleep affects sleep spindle occurrence, leading to the reduction or enhancement of slow oscillation-spindle (SO-spindle) coupling in NS and SWS, respectively. Optogenetic inhibition of pyramidal neurons in the frontal association cortex (FrA) during TMR abolishes the behavioral effects of NS-TMR and SWS-TMR by modulating SO-spindle coupling. Notably, calcium imaging of the L2/3 pyramidal neurons in the FrA shows that CS during SWS selectively enhances the activity of neurons previously activated during fear conditioning (FC+ neurons), which significantly correlates with CS-elicited spindle power spectrum density. Intriguingly, these TMR-induced calcium activity changes of FC+ neurons further correlate with mice freezing behavior, suggesting their contributions to the consolidation of fear memories. The findings indicate that TMR can selectively weaken or strengthen fear memory, in correlation with modulating SO-spindle coupling and the reactivation of FC+ neurons during substages of non-rapid eye movement (NREM) sleep.

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.

Rapid modulation in music supports attention in listeners with attentional difficulties

Background music is widely used to sustain attention, but little is known about what musical properties aid attention. This may be due to inter-individual variability in neural responses to music. Here we find that music with amplitude modulations added at specific rates can sustain attention differentially for those with varying levels of attentional difficulty. We first tested the hypothesis that music with strong amplitude modulation would improve sustained attention, and found it did so when it occurred early in the experiment. Rapid modulations in music elicited greater activity in attentional networks in fMRI, as well as greater stimulus-brain coupling in EEG. Finally, to test the idea that specific modulation properties would differentially affect listeners based on their level of attentional difficulty, we parametrically manipulated the depth and rate of amplitude modulations inserted in otherwise-identical music, and found that beta-range modulations helped more than other modulation ranges for participants with more ADHD symptoms. Results suggest the possibility of an oscillation-based neural mechanism for targeted music to support improved cognitive performance.

Coupling of Slow Oscillations in the Prefrontal and Motor Cortex Predicts Onset of Spindle Trains and Persistent Memory Reactivations

Sleep is known to drive the consolidation of motor memories. During nonrapid eye movement (NREM) sleep, the close temporal proximity between slow oscillations (SOs) and spindles ("nesting" of SO-spindles) is known to be essential for consolidation, likely because it is closely associated with the reactivation of awake task activity. Interestingly, recent work has found that spindles can occur in temporal clusters or "trains." However, it remains unclear how spindle trains are related to the nesting phenomenon. Here, we hypothesized that spindle trains are more likely when SOs co-occur in the prefrontal and motor cortex. We conducted simultaneous neural recordings in the medial prefrontal cortex (mPFC) and primary motor cortex (M1) of male rats training on the reach-to-grasp motor task. We found that intracortically recorded M1 spindles are organized into distinct temporal clusters. Notably, the occurrence of temporally precise SOs between mPFC and M1 was a strong predictor of spindle trains. Moreover, reactivation of awake task patterns is much more persistent during spindle trains in comparison with that during isolated spindles. Together, our work suggests that the precise coupling of SOs across mPFC and M1 may be a potential driver of spindle trains and persistent reactivation of motor memory during NREM sleep.

Temporal dynamics of negative emotional memory reprocessing during sleep

Memory reprocessing during sleep is a well-established phenomenon in numerous studies. However, it is unclear whether the intensity of memory reprocessing is consistently maintained throughout the night or exhibits dynamic changes. This study investigates the temporal dynamics of negative emotional memory reprocessing during sleep, with a specific focus on slow oscillation (SO)-spindle coupling and its role in memory reprocessing. In the first experiment (N = 40, mean age = 22.5 years), we detected the negative emotional memory reprocessing strength in each sleep cycle, we found that the 2nd sleep cycle after negative emotional memory learning constitute the most sensitive window for memory reprocessing, furthermore, SO-spindle coupling signals in this window plays a role in stabilizing negative emotional memory. To verify the role of SO-spindle coupling in negative emotional memory reprocessing, we utilized transcranial alternating current stimulation (tACS) to disrupt SO-spindle coupling during the 2nd sleep cycle (N = 21, mean age = 19.3 years). Notably, the outcomes of the tACS intervention demonstrated a significant reduction in the recognition of negative emotional memories. These findings offer new insights into the mechanisms that regulate emotional memory consolidation during sleep and may have implications for addressing psychiatric disorders associated with pathological emotional memory.

Effect of closed-loop vibration stimulation on sleep quality for poor sleepers

Introduction

Recent studies have investigated the autonomic modulation method using closed-loop vibration stimulation (CLVS) as a novel strategy for enhancing sleep quality. This study aimed to explore the effects of CLVS on sleep quality, autonomic regulation, and brain activity in individuals with poor sleep quality.

Methods

Twenty-seven participants with poor sleep quality (Pittsburgh sleep quality index >5) underwent two experimental sessions using polysomnography and a questionnaire, one with CLVS (STIM) and the other without (SHAM).

Results

Sleep macrostructure analysis first showed that CLVS significantly reduced the total time, proportion, and average duration of waking after sleep onset. These beneficial effects were paralleled by significantly increased self-reported sleep quality. Moreover, there was a significant increase in the normalized high-frequency (nHF) and electroencephalography relative powers of delta activity during N3 sleep under STIM. Additionally, coherence analysis between nHF and delta activity revealed strengthened coupling between cortical and cardiac oscillations.

Discussion

This study demonstrated that CLVS significantly improves sleep quality in individuals with poor sleep quality by enhancing both subjective and objective measures. These findings suggest that CLVS has the potential to be a practical, noninvasive tool for enhancing sleep quality in individuals with sleep disturbances, offering an effective alternative to pharmacological treatments.

Altered Cortical Information Interaction During Respiratory Events in Children with Obstructive Sleep Apnea-Hypopnea Syndrome

Obstructive sleep apnea-hypopnea syndrome (OSAHS) significantly impairs children's growth and cognition. This study aims to elucidate the pathophysiological mechanisms underlying OSAHS in children, with a particular focus on the alterations in cortical information interaction during respiratory events. We analyzed sleep electroencephalography before, during, and after events, utilizing Symbolic Transfer Entropy (STE) for brain network construction and information flow assessment. The results showed a significant increase in STE after events in specific frequency bands during N2 and rapid eye movement (REM) stages, along with increased STE during N3 stage events. Moreover, a noteworthy rise in the information flow imbalance within and between hemispheres was found after events, displaying unique patterns in central sleep apnea and hypopnea. Importantly, some of these alterations were correlated with symptom severity. These findings highlight significant changes in brain region coordination and communication during respiratory events, offering novel insights into OSAHS pathophysiology in children.

Sleep-dependent memory consolidation in young and aged brains

Young children and aged individuals are more prone to memory loss than young adults. One probable reason is insufficient sleep-dependent memory consolidation. Sleep timing and sleep-stage duration differ between children and aged individuals compared to adults. Frequent daytime napping and fragmented sleep architecture are common in children and older individuals. Moreover, sleep-dependent oscillations that play crucial roles in long-term memory storage differ among age groups. Notably, the frontal cortex, which is important for long-term memory storage undergoes major structural changes in children and aged subjects. The similarities in sleep dynamics between children and aged subjects suggest that a deficit in sleep-dependent consolidation contributes to memory loss in both age groups.

Optimizing real-time phase detection in diverse rhythmic biological signals for phase-specific neuromodulation

Closed-loop, phase-specific neurostimulation is a powerful method to modulate ongoing brain activity for clinical and research applications. Phase-specific stimulation relies on estimating the phase of an ongoing oscillation in real time and issuing a control command at a target phase. Phase detection algorithms based on Fast Fourier transform (FFT) are widely used due to their computational efficiency and robustness. However, it is unclear how algorithm performance depends on the spectral properties of the input signal and how algorithm parameters can be optimized. We used offline simulation to evaluate the performance of three algorithms (endpoint-corrected Hilbert Transform, Hilbert Transform and phase mapping) on three rhythmic biological signals with distinct spectral properties (rodent hippocampal theta potential, human EEG alpha and human essential tremor). First, we found that algorithm performance was more strongly influenced by signal amplitude and frequency variation compared with signal to noise ratio. Second, our simulations showed that the size of the data window for phase estimation was critical for the performance of FFT-based algorithms, where the optimal data window corresponds to the period of the oscillation. We validated this prediction with real time phase detection of hippocampal theta oscillations in freely behaving rats performing spatial navigation. Our findings define the relationship between signal properties and algorithm performance and provide a convenient method for optimizing FFT-based phase detection algorithms.

Acoustically evoked K-complexes together with sleep spindles boost verbal declarative memory consolidation in healthy adults

Over the past decade, phase-targeted auditory stimulation (PTAS), a neuromodulation approach which presents auditory stimuli locked to the ongoing phase of slow waves during sleep, has shown potential to enhance specific aspects of sleep functions. However, the complexity of PTAS responses complicates the establishment of causality between specific electroencephalographic events and observed benefits. Here, we used down-PTAS during sleep to specifically evoke the early, K-complex (KC)-like response following PTAS without leading to a sustained increase in slow-wave activity throughout the stimulation window. Over the course of two nights, one with down-PTAS, the other without, high-density electroencephalography (hd-EEG) was recorded from 14 young healthy adults. The early response exhibited striking similarities to evoked KCs and was associated with improved verbal memory consolidation via stimulus-evoked spindle events nested into the up-phase of ongoing 1 Hz waves in a central region. These findings suggest that the early, KC-like response is sufficient to boost memory, potentially by orchestrating aspects of the hippocampal-neocortical dialogue.

Targeted memory reactivation to augment treatment in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a psychiatric disorder with traumatic memories at its core. Post-treatment sleep may offer a unique time window to increase therapeutic efficacy through consolidation of therapeutically modified traumatic memories. Targeted memory reactivation (TMR) enhances memory consolidation by presenting reminder cues (e.g., sounds associated with a memory) during sleep. Here, we applied TMR in PTSD patients to strengthen therapeutic memories during sleep after one treatment session with eye movement desensitization and reprocessing (EMDR). PTSD patients received either slow oscillation (SO) phase-targeted TMR, using modeling-based closed-loop neurostimulation (M-CLNS) with EMDR clicks as a reactivation cue (n = 17), or sham stimulation (n = 16). Effects of TMR on sleep were assessed through high-density polysomnography. Effects on treatment outcome were assessed through subjective, autonomic, and fMRI responses to script-driven imagery (SDI) of the targeted traumatic memory and overall PTSD symptom level. Compared to sham stimulation, TMR led to stimulus-locked increases in SO and spindle dynamics, which correlated positively with PTSD symptom reduction in the TMR group. Given the role of SOs and spindles in memory consolidation, these findings suggest that TMR may have strengthened the consolidation of the EMDR-treatment memory. Clinically, TMR vs. sham stimulation resulted in a larger reduction of avoidance level during SDI. TMR did not disturb sleep or trigger nightmares. Together, these data provide first proof of principle that TMR may be a safe and viable future treatment augmentation strategy for PTSD. The required follow-up studies may implement multi-night TMR or TMR during REM sleep to further establish the clinical effect of TMR for traumatic memories.

Overcoming boundaries: Interdisciplinary challenges and opportunities in cognitive neuroscience

Cognitive neuroscience has considerable untapped potential to translate our understanding of brain function into applications that maintain, restore, or enhance human cognition. Complex, real-world phenomena encountered in daily life, professional contexts, and in the arts, can also be a rich source of information for better understanding cognition, which in turn can lead to advances in knowledge and health outcomes. Interdisciplinary work is needed for these bi-directional benefits to be realized. Our cognitive neuroscience team has been collaborating on several interdisciplinary projects: hardware and software development for brain stimulation, measuring human operator state in safety-critical robotics environments, and exploring emotional regulation in actors who perform traumatic narratives. Our approach is to study research questions of mutual interest in the contexts of domain-specific applications, using (and sometimes improving) the experimental tools and techniques of cognitive neuroscience. These interdisciplinary attempts are described as case studies in the present work to illustrate non-trivial challenges that come from working across traditional disciplinary boundaries. We reflect on how obstacles to interdisciplinary work can be overcome, with the goals of enriching our understanding of human cognition and amplifying the positive effects cognitive neuroscientists have on society and innovation.

A personalized semi-automatic sleep spindle detection (PSASD) framework

BACKGROUND

Sleep spindles are distinct electroencephalogram (EEG) patterns of brain activity that have been posited to play a critical role in development, learning, and neurological disorders. Manual scoring for sleep spindles is labor-intensive and tedious but could supplement automated algorithms to resolve challenges posed with either approaches alone.

NEW METHODS

A Personalized Semi-Automatic Sleep Spindle Detection (PSASD) framework was developed to combine the strength of automated detection algorithms and visual expertise of human scorers. The underlying model in the PSASD framework assumes a generative model for EEG sleep spindles as oscillatory components, optimized to EEG amplitude, with remaining signals distributed into transient and low-frequency components.

RESULTS

A single graphical user interface (GUI) allows both manual scoring of sleep spindles (model training data) and verification of automatically detected spindles. A grid search approach allows optimization of parameters to balance tradeoffs between precision and recall measures.

COMPARISON WITH EXISTING METHODS

PSASD outperformed DETOKS in F1-score by 19% and 4% on the DREAMS and P-DROWS-E datasets, respectively. It also outperformed YASA in F1-score by 25% in the P-DROWS-E dataset. Further benchmarking analysis showed that PSASD outperformed four additional widely used sleep spindle detectors in F1-score in the P-DROWS-E dataset. Titration analysis revealed that four 30-second epochs are sufficient to fine-tune the model parameters of PSASD. Associations of frequency, duration, and amplitude of detected sleep spindles matched those previously reported with automated approaches.

CONCLUSIONS

Overall, PSASD improves detection of sleep spindles in EEG data acquired from both younger healthy and older adult patient populations.