Sleep-A brain-state serving systems memory consolidation

Long-Term Visual Gist Abstraction Independent of Post-Encoding Sleep

Current theories of memory processing postulate a slow transformation from episodic to abstract, gist-like memories. We previously demonstrated that sleep shortly after learning improves gist abstraction in healthy volunteers across a one-year retention interval using a visual version of the Deese-Roediger-McDermott (DRM) paradigm. Here, we investigate the temporal evolution of this effect by testing recognition performance on a similar DRM task immediately after encoding, as well as 1 week and 1 year later. Moreover, we address the role of feature overlap during encoding, using stimulus sets that are either closely related to or more distant from their common prototype. Behavioural data were obtained from N = 16 healthy volunteers in a within-subjects design, where different sets of shapes were learned in separate experimental sessions, followed by consolidation during day-time wakefulness or nocturnal sleep, respectively. Our results indicate high levels of (false) recognition of non-encoded prototypes for all measurement points, including after 1 year. However, in contrast to our previous findings, gist memory was not affected by whether participants slept or stayed awake during the first 12 h after encoding. Comparisons across experiments indicate that the divergent results are due to changes in task demands rendering item and gist memory traces less distinct in the present study. Our results confirm the behavioural persistence of visual gist abstraction across extended intervals. At the same time, they highlight that sleep effects on this process are highly dependent on task demands.

Myelin: A possible proton capacitor for energy storage during sleep and energy supply during wakefulness

There are several physiological reasons why biological organisms sleep. One key one concerns brain metabolism. In our article we discuss the role of metabolism in myelin, based on the recent discovery that myelin contains mitochondrial components that enable the production of adenosine triphosphate (ATP) via oxidative phosphorylation (OXPHOS). These mitochondrial components in myelin probably originate from vesiculation of the mitochondrial membranes in form from mitochondrial derived vesicles (MDVs). We hypothesize that myelin acts as a proton capacitor, accumulating energy in the form of protons during sleep and converting it to ATP via OXPHOS during wakefulness. Empirical evidence supporting our hypothesis is discussed, including data on myelin metabolic activity, MDVs, and allometric scaling between white matter volume and sleep duration in mammals.

Connectivity in the Human Cerebral Cortex: A Fundamental Problem and a Possible Explanation for the Cognitive Power of Vertebrates

Recent electron microscopy reveals that weak synaptic connectivity predominates in the human cerebral cortex, raising the question of how information is transmitted by action potentials in these neural networks. Differences in field potential oscillations (brainwaves) and glia between vertebrates and invertebrates provide a possible answer that can also account for the incomparable increase in the cognitive ability of vertebrates.

Evolutionary learning in neural networks by heterosynaptic plasticity

Training biophysical neuron models provides insights into brain circuits' organization and problem-solving capabilities. Traditional training methods like backpropagation face challenges with complex models due to instability and gradient issues. We explore evolutionary algorithms (EAs) combined with heterosynaptic plasticity as a gradient-free alternative. Our EA models agents with distinct neuron information routes, evaluated via alternating gating, and guided by dopamine-driven plasticity. This model draws inspiration from various biological mechanisms, such as dopamine function, dendritic spine meta-plasticity, memory replay, and cooperative synaptic plasticity within dendritic neighborhoods. Neural networks trained with this model recapitulate brain-like dynamics during cognition. Our method effectively trains spiking and analog neural networks in both feedforward and recurrent architectures, it also achieves performance in tasks like MNIST classification and Atari games comparable to gradient-based methods. Overall, this research extends training approaches for biophysical neuron models, offering a robust alternative to traditional algorithms.

Awake reactivation of cortical memory traces predicts subsequent memory retrieval

Brief periods of rest after learning facilitate consolidation of new memories. Memory reactivation and hippocampal-cortical dialogue have been proposed as candidate mechanisms supporting consolidation. However, the study of these mechanisms has mostly concerned sleep-based consolidation. Whether and how awake reactivation can selectively consolidate cortical memory traces to guide subsequent behavior requires more human electrophysiological evidence. This study addressed these issues by utilizing intracranial electroencephalography (iEEG) recordings from 11 patients with drug-resistant epilepsy, who learned a set of object-location associations. Using representational similarity analysis, we found that, among the multiple cortical memory traces of object-location associations for the same object generated through several rounds of learning, the association corresponding to memory traces with stronger cortical activation during wakeful rest was more likely to be retrieved later. Awake reactivation of cortical memory trace was accompanied by increased hippocampal ripple rates and enhanced theta-band hippocampal-cortical communication, with hippocampal interactions with cortical regions within the default mode network preceding cortical reactivation. Together, these results suggest that awake reactivation of cortical memory trace during post-learning rest supports memory consolidation, predicting subsequent recall.

The Association Between Sleep Health and a History of Cataract Surgery in the United States Based on the National Health and Nutrition Examination Survey (NHANES) 2005-2008

Background: The aim of this study was to assess the relationship between sleep-related variables (sleep duration, sleep trouble, and sleep disorder), comprehensive sleep patterns, and the reported history of cataract surgery in the U.S. population aged 20 years and older. Methods: We utilized data from the National Health and Nutrition Examination Survey (NHANES) 2005-2008 database. First, we analyzed the association between covariates and the reported history of cataract surgery using univariable Poisson regression. Subsequently, we constructed three models to evaluate the association between sleep-related variables and the reported history of cataract surgery using multivariable Poisson regression. Subgroup analyses were conducted to determine whether the association between sleep and the reported history of cataract surgery exhibited heterogeneity. Finally, we performed a sensitivity analysis to assess the stability of the results. Results: A total of 8591 participants were included in this study, among whom 774 had a history of cataract surgery. After adjusting for all covariates, participants experiencing sleep trouble had a higher prevalence of reported history of cataract surgery than participants without sleep trouble [PR = 1.40; 95%CI = (1.22, 1.62)]. Regarding combined sleep, participants with poor sleep patterns had a 36% higher prevalence of reported history of cataract surgery than those with healthy sleep patterns [PR = 1.36; 95%CI = (1.13, 1.64)]. The results of the sensitivity analysis indicate that the relationship between sleep patterns and the reported history of cataract surgery is robust. Conclusions: Sleep trouble and poor sleep patterns are positively linked to the high prevalence of a reported history of cataract surgery. Further research is needed to explore the underlying mechanisms.

Sleep stages antagonistically modulate reactivation drift

Hippocampal reactivation of waking neuronal assemblies in sleep is a key initial step of systems consolidation. Nevertheless, it is unclear whether reactivated assemblies are static or whether they reorganize gradually over prolonged sleep. We tracked reactivated CA1 assembly patterns over ∼20 h of sleep/rest periods and related them to assemblies seen before or after in a spatial learning paradigm using rats. We found that reactivated assembly patterns were gradually transformed and started to resemble those seen in the subsequent recall session. Periods of rapid eye movement (REM) sleep and non-REM (NREM) had antagonistic roles: whereas NREM accelerated the assembly drift, REM countered it. Moreover, only a subset of rate-changing pyramidal cells contributed to the drift, whereas stable-firing-rate cells maintained unaltered reactivation patterns. Our data suggest that prolonged sleep promotes the spontaneous reorganization of spatial assemblies, which can contribute to daily cognitive map changes or encoding new learning situations.

The predictive nature of spontaneous brain activity across scales and species

Emerging research suggests the brain operates as a "prediction machine," continuously anticipating sensory, motor, and cognitive outcomes. Central to this capability is the brain's spontaneous activity-ongoing internal processes independent of external stimuli. Neuroimaging and computational studies support that this activity is integral to maintaining and refining mental models of our environment, body, and behaviors, akin to generative models in computation. During rest, spontaneous activity expands the variability of potential representations, enhancing the accuracy and adaptability of these models. When performing tasks, internal models direct brain regions to anticipate sensory and motor states, optimizing performance. This review synthesizes evidence from various species, from C. elegans to humans, highlighting three key aspects of spontaneous brain activity's role in prediction: the similarity between spontaneous and task-related activity, the encoding of behavioral and interoceptive priors, and the high metabolic cost of this activity, underscoring prediction as a fundamental function of brains across species.

Slow wave synchrony during NREM sleep tracks cognitive impairment in prodromal Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) disrupts human sleep architecture more severely than normal aging. However, it remains unclear how AD changes oscillatory neural activity during sleep, and whether such changes foreshadow cognitive decline in AD.

METHODS

We used high-density electroencephalography sleep recordings in 55 participants: (1) 21 healthy older adults, (2) 28 patients with amnestic mild cognitive impairment (aMCI)-a prodromal AD stage, and (3) 6 AD patients.

RESULTS

Cognitive performance robustly decreases with the slow wave (SW) trough amplitude and its synchronization across broad frontocentral cortical areas. Thus, across the AD spectrum, slow wave synchrony declines with cognition, as in normal aging, but at an accelerated pace. Moreover, delayed rapid eye movement (REM) sleep onset in aMCI and AD patients was associated with deficient SW activity, suggesting insufficiently restorative non-REM sleep.

DISCUSSION

These findings suggest that impaired slow waves are closely linked to cognitive impairment and mark disrupted neural activity in AD progression.

HIGHLIGHTS

Detailed analysis of high-density sleep electroencephalography was performed in amnestic mild cognitive impairment and Alzheimer's disease (AD) patients. Cognitive status robustly correlates with slow wave trough and its cortical spread. Delayed rapid eye movement sleep onset associated with AD correlates with diminished slow wave troughs. Impaired slow waves mark progressively disrupted neural activity in prodromal AD.

Monoaminergic signaling during mammalian NREM sleep - Recent insights and next-level questions

Subcortical neuromodulatory activity in the mammalian brain enables flexible wake behaviors, which are essential for survival in an ever-changing external environment. With the suppression of such behaviors in sleep, this activity is, on average, much reduced. Recent discoveries, enabled by unprecedented technical advancements, challenge the long-standing view that monoaminergic systems-noradrenaline (NA), dopamine (DA), and serotonin (5-HT)-remain largely inactive during sleep. This review highlights recent technological and scientific progress in this field, summarizing evidence that monoaminergic signaling in the brain supplements sleep with essential wake-related functions. Stress and/or neuropsychiatric conditions negatively impact on monoaminergic signaling, which can lead to sleep disruptions. Furthermore, subcortical neuromodulatory systems are vulnerable to neurodegenerative pathologies, which implies them in sleep disruptions at early stages of disease. We propose that future research will be well-invested in elucidating the spatiotemporal organization, cellular mechanisms, and functional relevance of neuromodulatory dynamics across species, and in identifying the molecular and physiological processes that sustain their integrity throughout the lifespan.

Latent mechanisms of plasticity are upregulated during sleep

Sleep is thought to serve an important role in learning and memory, but the mechanisms by which sleep promotes plasticity remain unclear. Even in the absence of plastic changes in neuronal function, many molecular, cellular, and physiological processes linked to plasticity are upregulated during sleep. Therefore, sleep may be a state in which latent plasticity mechanisms are poised to respond following novel experiences during prior wake. Many of these plasticity-related processes can promote both synaptic strengthening and weakening. Signaling pathways activated during sleep may interact with complements of proteins, determined by the content of prior waking experience, to establish the polarity of plasticity. Furthermore, precise reactivation of neuronal spiking patterns during sleep may interact with ongoing neuromodulatory, dendritic, and network activity to strengthen and weaken synapses. In this review, we will discuss the idea that sleep elevates latent plasticity mechanisms, which drive bidirectional plasticity depending on prior waking experience.

Effects of word list length during episodic memory encoding observation by the event-related potential and time-frequency

The present study explored the effects of word list length during the encoding of visual verbal stimuli. The participants received Latvian nouns in lists of different lengths: short (up to 29), medium (30-59), and long (60-160). During the presentation of visual stimuli, the 19-channel EEG was recorded with a sample rate of 512 Hz and cut-off frequencies of 0.1-50 Hz. The memory encoding process was analyzed with the event-related potential (ERP) and time-frequency (TF) methods for selected regions of interest (ROI) electrodes F3, F7, C3, P3, T3, and T5 in the 10-20 system corresponding to language processing brain areas. We compared ERP and TF data regarding the list length in the -100 ms to 700 ms time window. ROI electrodes T3, T5, and P3 indicated significantly different involvement of language processing areas under different list lengths by ERP observation. More lateralized regions (F7, T3) provided evidence for more pronounced differences in the encoding process than less lateralized regions (F3, C3). The analysis of TF revealed differences in theta, alpha, and beta wave bands in the F3 and P3 channels. Medium lists demonstrated higher differences from short and long lists, indicating a nonlinear trend in the involvement of language-processing regions.

Food intake enhances hippocampal sharp wave-ripples

Effective regulation of energy metabolism is critical for survival. Metabolic control involves various nuclei within the hypothalamus, which receive information about the body's energy state and coordinate appropriate responses to maintain homeostasis, such as thermogenesis, pancreatic insulin secretion, and food-seeking behaviors. It has recently been found that the hippocampus, a brain region traditionally associated with memory and spatial navigation, is also involved in metabolic regulation. Specifically, hippocampal sharp wave-ripples (SWRs), which are high-frequency neural oscillations supporting memory consolidation and foraging decisions, have been shown to reduce peripheral glucose levels. However, whether SWRs are enhanced by recent feeding-when the need for glucose metabolism increases, and if so, whether feeding-dependent modulation of SWRs is communicated to other brain regions involved in metabolic regulation-remains unknown. To address these gaps, we recorded SWRs from the dorsal CA1 region of the hippocampus of mice during sleep sessions before and after consumption of meals of varying caloric values. We found that SWRs occurring during sleep are significantly enhanced following food intake, with the magnitude of enhancement being dependent on the caloric content of the meal. This pattern occurred under both food-deprived and ad libitum feeding conditions. Moreover, we demonstrate that GABAergic neurons in the lateral hypothalamus, which are known to regulate food intake, exhibit a robust SWR-triggered increase in activity. These findings identify the satiety state as a factor modulating SWRs and suggest that hippocampal-lateral hypothalamic communication is a potential mechanism by which SWRs could modulate peripheral metabolism and food intake.

A time window for memory consolidation during NREM sleep revealed by cAMP oscillation

Memory formation requires specific neural activity in coordination with intracellular signaling mediated by second messengers such as cyclic adenosine monophosphate (cAMP). However, the real-time dynamics of cAMP remain largely unknown. Here, using a genetically encoded cAMP sensor with high temporal resolution, we found neural-activity-dependent rapid cAMP elevation during learning. Interestingly, in slow-wave sleep, during which memory consolidation occurs, the cAMP level in mice was anti-correlated with neural activity and exhibited norepinephrine β1 receptor-dependent infra-slow oscillations that were synchronized across the hippocampus and cortex. Furthermore, the hippocampal-cortical interactions increased during the narrow time-window of the peak cAMP level; suppressing hippocampal activity specifically during this window impaired spatial memory consolidation. Thus, hippocampal-dependent memory consolidation occurs within a specific time window of high cAMP activity during slow-wave sleep.

Sleep loss is a metabolic disorder

Sleep loss dysregulates cellular metabolism and energy homeostasis. Highly metabolically active cells, such as neurons, enter a catabolic state during periods of sleep loss, which consequently disrupts physiological functioning. Specific to the central nervous system, sleep loss results in impaired synaptogenesis and long-term memory, effects that are also characteristic of neurodegenerative diseases. In this review, we describe how sleep deprivation increases resting energy expenditure, leading to the development of a negative energy balance-a state with insufficient metabolic resources to support energy expenditure-in highly active cells like neurons. This disruption of energetic homeostasis alters the balance of metabolites, including adenosine, lactate, and lipid peroxides, such that energetically costly processes, such as synapse formation, are attenuated. During sleep loss, metabolically active cells shunt energetic resources away from those processes that are not acutely essential, like memory formation, to support cell survival. Ultimately, these findings characterize sleep loss as a metabolic disorder.

Sleep selectively and durably enhances memory for the sequence of real-world experiences

Sleep is thought to play a critical role in the retention of memory for past experiences (episodic memory), reducing the rate of forgetting compared with wakefulness. Yet it remains unclear whether and how sleep actively transforms the way we remember multidimensional real-world experiences, and how such memory transformation unfolds over the days, months and years that follow. In an exception to the law of forgetting, we show that sleep actively and selectively improves the accuracy of memory for a one-time, real-world experience (an art tour)-specifically boosting memory for the order of tour items (sequential associations) versus perceptual details from the tour (featural associations). This above-baseline boost in sequence memory was not evident after a matched period of wakefulness. Moreover, the preferential retention of sequence relative to featural memory observed after a night's sleep grew over time up to 1 year post-encoding. Finally, overnight polysomnography showed that sleep-related memory enhancement was associated with the duration and neurophysiological hallmarks of slow-wave sleep previously linked to sequential neural replay, particularly spindle-slow wave coupling. These results suggest that sleep serves a crucial and selective role in enhancing sequential organization in our memory for past events at the expense of perceptual details, linking sleep-related neural mechanisms to the days-to-years-long transformation of memory for complex real-life experiences.

Data Uncertainty (DU)-Former: An Episodic Memory Electroencephalography Classification Model for Pre- and Post-Training Assessment

Episodic memory training plays a crucial role in cognitive enhancement, particularly in addressing age-related memory decline and cognitive disorders. Accurately assessing the effectiveness of such training requires reliable methods to capture changes in memory function. Electroencephalography (EEG) offers an objective way of evaluating neural activity before and after training. However, EEG classification in episodic memory assessment remains challenging due to the variability in brain responses, individual differences, and the complex temporal-spatial dynamics of neural signals. Traditional EEG classification methods, such as Support Vector Machines (SVMs) and Convolutional Neural Networks (CNNs), face limitations when applied to episodic memory training assessment, struggling to extract meaningful features and handle the inherent uncertainty in EEG signals. To address these issues, this paper introduces DU-former, which improves feature extraction and enhances the model's robustness against noise. Specifically, data uncertainty (DU) explicitly handles data uncertainty by modeling input features as Gaussian distributions within the reparameterization module. One branch predicts the mean through convolution and normalization, while the other estimates the variance via average pooling and normalization. These values are then used for Gaussian reparameterization, enabling the model to learn more robust feature representations. This approach allows the model to remain stable when dealing with complex or noisy data. To validate the method, an episodic memory training experiment was designed with 17 participants who underwent 28 days of training. Behavioral data showed a significant reduction in task completion time. Object recognition accuracy also improved, as indicated by the higher proportion of correctly identified target items in the episodic memory testing game. Furthermore, EEG data collected before and after the training were used to evaluate the DU-former's performance, demonstrating significant improvements in classification accuracy. This paper contributes by introducing uncertainty learning and proposing a more efficient and robust method for EEG signal classification, demonstrating superior performance in episodic memory assessment.

Preoperative Sleep Deprivation Exacerbates Anesthesia/Surgery-induced Abnormal GABAergic Neurotransmission and Neuronal Damage in the Hippocampus in Aged Mice

Older adults with anesthesia and surgery often suffer from postoperative cognitive dysfunction (POCD), which puts a heavy burden on rehabilitation. Preoperative sleep disorder, a common phenomenon in elderly anesthesia patients, is closely associated with POCD, but the underlying mechanism is still not fully understood. Hippocampal gamma-aminobutyric acid (GABA)ergic neurotransmission has been reported to play an important role in sleep disorder and cognitive impairment. The aim of this study was to elucidate the effect of preoperative acute sleep deprivation (SD) on anesthesia/surgery-induced POCD and the potential mechanism of hippocampal GABAergic neurotransmission. In the aged (18-20-month-old) male mice, we used a rotating rod to deprive sleep for 24 h and induced a POCD model using sevoflurane exposure combined with laparotomy exploration. A sequential set of behavioral tests, including open field test (OFT), Y-maze, and novel object recognition (NOR), was conducted to assess cognitive performances. In vivo magnetic resonance imaging (MRI) technique was used to observe hippocampal axonal microstructural changes. The levels of GABAergic neurotransmitter markers glutamic acid decarboxylase (GAD) 67, vesicular GABA transporter (VGAT), GABA transporter (GAT)-1, and GABA in the hippocampus were detected with enzyme-linked immunosorbent assay (ELISA). The reactivity of GABAergic neurons and neuronal damage in different subregions of the hippocampus were observed by immunofluorescence and Nissl staining, respectively. Compared the anesthesia/surgery (A/S) mice, 24-h SD combined with A/S induced shorter stay time in the central area of the open field, less the percent of novel arm preference in the Y maze, and lower recognition index in the NOR, as well as significantly enhanced hippocampal GABAergic neurotransmission, decreased hippocampal axonal integrity and density, and increased GAD67 reactivity and reduced the number of neurons in hippocampal CA1. Preoperative 24-h SD exacerbated anesthesia/surgery-induced POCD in aged mice, with the cumulative effect of abnormal GABAergic neurotransmission and neuronal damage in the hippocampus.

Does Obstructive sleep apnea mediate the risk of cognitive impairment by expanding the perivascular space?

BACKGROUND

Obstructive sleep apnea (OSA) is a neglected global health issue and when left untreated could lead to cognitive impairment (CI), one of the most burdensome outcomes of OSA. Enlarged perivascular spaces (EPVS), an imaging feature as well as a subtype of cerebral small vessel disease and integral part of CSVD, are associated with cognitive function, but the relationship between EPVS and CI is not well understood and by extension the correlation between OSA and EPVS, how CI develops under the joint impact of OSA and EPVS remains unclear. It is the goal of This study to explore the associations among OSA, EPVS, and CI.

METHODS

This cross-sectional study included 175 older adults with imaging features of EPVS with or without other CSVD subtype features by cranial magnetic resonance imaging between January 2021 and June 2023 at the Shanghai Fifth People's Hospital. We assessed OSA using polysomnography. Blood samples were collected to determine vascular risk factor indices. Cognitive scoring modalities included the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MOCA). To explore the relationship among OSA, EPVS, and CI, we used single-factor analysis, multifactorial analysis, and receiver operating characteristic (ROC) curves.

RESULTS

A total of 136 participants were analyzed. In our statistical process, MMSE showed a more distinguished performance than MoCA. Participants with OSA had greater EPVS burdens in the midbrain (p < 0.001) and hippocampus (p < 0.001) and more serious CI (p = 0.001). OSA positively influenced EPVS in the midbrain (β = 0.052; 95% confidence interval [CI]: 0.006, 0.097; p = 0.026) and hippocampus (β = 0.190, 95% CI: 0.104, 0.275, p < 0.001). Moreover, the apnea-hypopnea index (AHI; β = -0.514; 95% CI: -0.077, -0.031; p < 0.001) negatively affected cognitive e function. With each increase in the AHI by 1 unit, the risk of CI increased by 12.0% (odds ratio = 1.120; 95%CI: 1.062, 1.181; p < 0.001). The AHI (sensitivity, 67.20%; specificity, 92.20%; area under the ROC curve, 0.828; p < 0.001) had a certain degree of accuracy in ruling out CI in the EPVS population, as calculated using the ROC curve.

CONCLUSIONS

We identified significant relations among OSA, EPVS, and CI. The AHI is a potential marker for estimating cognitive function in patients with EPVS.

Electrophysiological signatures underlying variability in human memory consolidation

We experience countless pieces of new information each day, but remembering them later depends on firmly instilling memory storage in the brain. Numerous studies have implicated non-rapid eye movement (NREM) sleep in consolidating memories via interactions between hippocampus and cortex. However, the temporal dynamics of this hippocampal-cortical communication and the concomitant neural oscillations during memory reactivations remains unclear. To address this issue, the present study used the procedure of targeted memory reactivation (TMR) following learning of object-location associations to selectively reactivate memories during human NREM sleep. Cortical pattern reactivation and hippocampal-cortical coupling were measured with intracranial EEG recordings in patients with epilepsy. We found that TMR produced variable amounts of memory enhancement across a set of object-location associations. Successful TMR increased hippocampal ripples and cortical spindles, apparent during two discrete sweeps of reactivation. The first reactivation sweep was accompanied by increased hippocampal-cortical communication and hippocampal ripple events coupled to local cortical activity (cortical ripples and high-frequency broadband activity). In contrast, hippocampal-cortical coupling decreased during the second sweep, while increased cortical spindle activity indicated continued cortical processing to achieve long-term storage. Taken together, our findings show how dynamic patterns of item-level reactivation and hippocampal-cortical communication support memory enhancement during NREM sleep.

The Guardian of Dreams: The Neglected Relationship Between Sleep and Psychoanalysis

Knowledge about sleep was very limited at the time when Freud published his seminal work on the interpretation of dreams. He was also not interested in sleep, which was considered a problem of physiology; however, sleep appears to have a central role in his model, since dreaming is considered the guardian of sleep. The function of dreaming, according to Freud, is to protect sleep from disruption, with the dream working to avoid repressed stimuli interrupting the "biological" function of sleep. Before neurophysiological studies provided evidence that sleep is not a passive state, Freud also recognized sleep as an active process, as human beings voluntarily withdraw their attention from the external world to actively move to sleep. The discovery of REM sleep in the 1950s led psychoanalysts to see sleep as the necessary background to the occurrence of dreaming. Although Freud dismissed the clinical importance of sleep disturbances, viewing them as the somatic expression of an instinctual disturbance which would disappear during psychoanalytic treatment, successive authors highlighted the fact that sleep disturbances might have a more specific psychological significance. The similarities between the loss of self that occurs during sleep and the fragmentation of the identity experienced during schizophrenia represent an interesting and yet not fully explored area of research. Thanks to Freud's work, the desire to sleep assumes the important role of a psychological, active factor that contributes to the occurrence and function of sleep.

Song-like activation of syringeal and respiratory muscles during sleep in canaries

Sleep replay activity involves the reactivation of brain structures with patterns similar to those observed during waking behavior. In this study, we demonstrate that adult male canaries exhibit spontaneous, song-like peripheral reactivation during night sleep. Our findings include: (1) the presence of activity in respiratory muscles, leading to song-like air sac pressure patterns of low amplitude, (2) the simultaneous occurrence of respiratory replay events and reactivation of syringeal muscles, and (3) the reactivation of syringeal muscles without concurrent respiratory system activity. This song-like reactivation of peripheral motor systems enables the identification of specific motor patterns, with replay events preserving individual morphological and temporal properties. The activation of peripheral motor systems in songbirds and the differences in activation patterns between species give unique insights into the fictive behavioral output of activation of a complex learned motor behavior during sleep, shedding light on the neural control mechanisms and potential functions.

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.

Food intake enhances hippocampal sharp wave-ripples

Effective regulation of energy metabolism is critical for survival. Metabolic control involves various nuclei within the hypothalamus, which receive information about the body's energy state and coordinate appropriate responses to maintain homeostasis, such as thermogenesis, pancreatic insulin secretion, and food-seeking behaviors. It has recently been found that the hippocampus, a brain region traditionally associated with memory and spatial navigation, is also involved in metabolic regulation. Specifically, hippocampal sharp wave ripples (SWRs), which are high-frequency neural oscillations supporting memory consolidation and foraging decisions, have been shown to reduce peripheral glucose levels. However, whether SWRs are enhanced by recent feeding-when the need for glucose metabolism increases, and if so, whether feeding-dependent modulation of SWRs is communicated to other brain regions involved in metabolic regulation, remains unknown. To address these gaps, we recorded SWRs from the dorsal CA1 region of the hippocampus of mice during sleep sessions before and after consumption of meals of varying caloric values. We found that SWRs occurring during sleep are significantly enhanced following food intake, with the magnitude of enhancement being dependent on the caloric content of the meal. This pattern occurred under both food-deprived and ad libitum feeding conditions. Moreover, we demonstrate that GABAergic neurons in the lateral hypothalamus, which are known to regulate food intake, exhibit a robust SWR-triggered increase in activity. These findings identify the satiety state as a factor modulating SWRs and suggest that hippocampal-lateral hypothalamic communication is a potential mechanism by which SWRs could modulate peripheral metabolism and food intake.

Anything but small: Microarousals stand at the crossroad between noradrenaline signaling and key sleep functions

Continuous sleep restores the brain and body, whereas fragmented sleep harms cognition and health. Microarousals (MAs), brief (3- to 15-s-long) wake intrusions into sleep, are clinical markers for various sleep disorders. Recent rodent studies show that MAs during healthy non-rapid eye movement (NREM) sleep are driven by infraslow fluctuations of noradrenaline (NA) in coordination with electrophysiological rhythms, vasomotor activity, cerebral blood volume, and glymphatic flow. MAs are hence part of healthy sleep dynamics, raising questions about their biological roles. We propose that MAs bolster NREM sleep's benefits associated with NA fluctuations, according to an inverted U-shaped curve. Weakened noradrenergic fluctuations, as may occur in neurodegenerative diseases or with sleep aids, reduce MAs, whereas exacerbated fluctuations caused by stress fragment NREM sleep and collapse NA signaling. We suggest that MAs are crucial for the restorative and plasticity-promoting functions of sleep and advance our insight into normal and pathological arousal dynamics from sleep.

Tonic-clonic seizures induce hypersomnia and suppress rapid eye movement sleep in mouse models of epilepsy

The reciprocal relationship between sleep and epilepsy has been reported by numerous clinical studies. However, the underlying neural mechanisms are poorly understood. Animal models of epilepsy are powerful tools to tackle this question. A lagging research area is the understudied sleep in epilepsy models. Here, we characterize sleep architecture and its relationship with seizures in a mouse model of sleep-related hypermotor epilepsy, caused by mutation of KCNT1. We demonstrated that nocturnal tonic-clonic seizures induce more non-rapid eye movement (NREM) sleep but suppress rapid eye movement (REM) sleep, resulting in altered sleep architecture in this mouse model. Importantly, the seizure number is quantitatively anticorrelated with the amount of REM sleep. Strikingly, this modulation of NREM and REM sleep states can be repeated in another mouse model of epilepsy with diurnal tonic-clonic seizures. Together, our findings provide evidence from rodent models to substantiate the close interplay between sleep and epilepsy, which lays the ground for mechanistic studies.

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.

Amylopectin-based Hydrogel Probes for Brain-machine Interfaces

Implantable neural probes hold promise for acquiring brain data, modulating neural circuits, and treating various brain disorders. However, traditional implantable probes face significant challenges in practical applications, such as balancing sensitivity with biocompatibility and the difficulties of in situ neural information monitoring and neuromodulation. To address these challenges, this study developed an implantable hydrogel probe capable of recording neural signals, modulating neural circuits, and treating stroke. Amylopectin is integrated into the hydrogels, which can induce reorientation of the poly(3,4-ethylenedioxythiophene) (PEDOT) chain and create compliant interfaces with brain tissues, enhancing both sensitivity and biocompatibility. The hydrogel probe shows the capability of continuously recording deep brain signals for 8 weeks. The hydrogel probe is effectively utilized to study deep brain signals associated with various physiological activities. Neuromodulation and neural signal monitoring are performed directly in the primary motor cortex of rats, enabling control over their limb behaviors through evoked signals. When applied to the primary motor cortex of stroke-affected rats, neuromodulation significantly reduced the brain infarct area, promoted synaptic reorganization, and restored motor functions and balance. This research represents a significant scientific breakthrough in the design of neural probes for brain monitoring, neural circuit modulation, and the development of brain disease therapies.

Association of rapid eye movement sleep latency with multimodal biomarkers of Alzheimer's disease

INTRODUCTION

Sleep disturbances are associated with Alzheimer's disease (AD) and Alzheimer's disease and related dementias (ADRD), but the relationship between sleep architecture, particularly rapid eye movement (REM) sleep, and AD/ADRD biomarkers remains unclear.

METHODS

We enrolled 128 adults (64 with Alzheimer's disease, 41 with mild cognitive impairment [MCI], and 23 with normal cognition [NC]), mean age 70.8 ± 9.6 years, 56.9% female, from a tertiary hospital in China. Participants underwent overnight polysomnography (PSG), amyloid β (Aβ) positron emission tomography (PET), and plasma biomarker analysis: phosphorylated tau at threonine 181 (p-tau181), neurofilament light (NfL), and brain-derived neurotrophic factor (BDNF).

RESULTS

After adjusting for demographics, apolipoprotein E (APOE) ε4 status, cognition, and comorbidities, the highest tertile of REM latency was associated with higher Aβ burden (β = 0.08, 95% confidence interval [CI]: 0.03 to 0.13, p = 0.002), elevated p-tau181 (β = 0.19, 95% CI: 0.02 to 0.13, p = 0.002), and reduced BDNF levels (β = -0.47, 95% CI: -0.68 to -0.13, p = 0.013), compared to the lowest tertile.

DISCUSSION

Prolonged REM latency may serve as a novel marker or risk factor for AD/ADRD pathogenesis.

HIGHLIGHTS

Rapid eye movement latency (REML) may be a potential marker for Alzheimer's disease and Alzheimer's disease and related dementias (AD/ADRD) pathogenesis. Prolonged REML was associated with higher amyloid beta (Aβ) burden, phosphorylated tau-181 (p-tau181), and lower brain-derived neurotrophic factor (BDNF) levels. Intervention trial is needed to determine if targeting REML can modify AD/ADRD risk. Slow-wave sleep was not associated with AD/ADRD biomarkers.

Slow Oscillation-Spindle Coupling Predicts Sequence-Based Language Learning

Sentence comprehension involves the decoding of both semantic and grammatical information, a process fundamental to communication. As with other complex cognitive processes, language comprehension relies, in part, on long-term memory. However, the electrophysiological mechanisms underpinning the encoding and generalization of higher-order linguistic knowledge remain elusive, particularly from a sleep-based consolidation perspective. One candidate mechanism that may support the consolidation of higher-order language is the coordination of slow oscillations (SO) and sleep spindles during nonrapid eye movement sleep (NREM). To examine this hypothesis, we analyzed electroencephalographic (EEG) data recorded from 35 participants (M age = 25.4; SD = 7.10; 16 males) during an artificial language learning task, contrasting performance between individuals who were given an 8 h nocturnal sleep period or an equivalent period of wake. We found that sleep relative to wake was associated with superior performance for sequence-based word order rules. Postsleep sequence-based word order processing was further associated with less task-related theta desynchronization, an electrophysiological signature of successful memory consolidation, as well as cognitive control and working memory. Frontal NREM SO-spindle coupling was also positively associated with behavioral sensitivity to sequence-based word order rules, as well as with task-related theta power. As such, theta activity during retrieval of previously learned information correlates with SO-spindle coupling, thus linking neural activity in the sleeping and waking brain. Taken together, this study presents converging behavioral and neurophysiological evidence for a role of NREM SO-spindle coupling and task-related theta activity as signatures of memory consolidation and retrieval in the context of higher-order language learning.

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.

Different regulative effects of high- and low-frequency external trigeminal nerve stimulation (eTNS) on sleep activity: Preliminary study

STUDY OBJECTIVE

With the growing prominence of peripheral nerve stimulation technology, the clinical applications and potential neurophysiological mechanisms of external trigeminal nerve stimulation (eTNS) have garnered increasing attention. Despite its status as the sole neuromodulation method commonly employed in sleep, no studies have explored the effects of eTNS at varying frequencies on sleep activities. This study aims to investigate the regulatory effects of high-frequency and low-frequency eTNS on sleep activities using polysomnography.

METHODS

In this within-subjects experiment, 20 participants underwent a night of adaptation sleep, followed by 8-h sessions of sham, 120Hz-, and 2Hz-eTNS interventions in a randomized order in the sleep laboratory, with polysomnographic signals collected throughout.

RESULTS

The results indicated that 120Hz-eTNS significantly improved sleep efficiency, increased N2 sleep proportion, and reduced sleep latency, without significantly affecting sleep stage transition probabilities, sleep duration, or sleep-specific wave activities. Conversely, while 2Hz-eTNS did not impact sleep efficiency or latency, it increased the proportion of N3 sleep, stabilizes N3 sleep, and enhanced the survival probability of N3 and REM sleep duration. Additionally, it increases the density of slow oscillations (SOs), improved the coupling ratio of SO-spindles, and enhanced coupling timing accuracy.

CONCLUSIONS

These findings suggest that eTNS during sleep can indeed modulate sleep activities, with different frequencies exerting distinct regulatory effects. This may hold significant value for advancing the clinical application and efficacy of eTNS.

Infraslow noradrenergic locus coeruleus activity fluctuations are gatekeepers of the NREM-REM sleep cycle

The noradrenergic locus coeruleus (LC) regulates arousal levels during wakefulness, but its role in sleep remains unclear. Here, we show in mice that fluctuating LC neuronal activity partitions non-rapid-eye-movement sleep (NREMS) into two brain-autonomic states that govern the NREMS-REMS cycle over ~50-s periods; high LC activity induces a subcortical-autonomic arousal state that facilitates cortical microarousals, whereas low LC activity is required for NREMS-to-REMS transitions. This functional alternation regulates the duration of the NREMS-REMS cycle by setting permissive windows for REMS entries during undisturbed sleep while limiting these entries to maximally one per ~50-s period during REMS restriction. A stimulus-enriched, stress-promoting wakefulness was associated with longer and shorter levels of high and low LC activity, respectively, during subsequent NREMS, resulting in more microarousal-induced NREMS fragmentation and delayed REMS onset. We conclude that LC activity fluctuations are gatekeepers of the NREMS-REMS cycle and that this role is influenced by adverse wake experiences.

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.

Effects of Melissa officinalis Phytosome on Sleep Quality: Results of a Prospective, Double-Blind, Placebo-Controlled, and Cross-Over Study

BACKGROUND

Melissa officinalis standardised extracts, characterised by the presence of hydroxycinnamic acids, have been experimentally demonstrated to be endowed with anti-anxiety and anti-insomnia pharmacological actions. These effects, probably attributable, at least in part, to the role played by rosmarinic acid on GABA-T, have not always been observed in a reproducible manner in humans, perhaps due to the poor bioavailability of these compounds.

METHODS

as nutraceuticals and botanicals could be an alternative option to prescription medications for alleviating symptoms of mild anxiety and insomnia, we have verified in a prospective, double-blind, placebo-controlled, and cross-over study the supporting role on sleep quality played by a Melissa officinalis highly standardised extract, formulated as Phytosome™ (MOP) to improve the oral bioavailability of its active polyphenolic components.

RESULTS

results showed a significant reduction in the ISI score in the treated group, with an average of 6.8 ± 4.1 compared to 9.7 ± 3.7 in the placebo group, indicating a significant reduction of 2.9 points (p = 0.003). The SWS phase duration increased by an average of 15%, while the REM phase decreased by 10%. Additionally, 87% of participants in the treated group reported improved sleep quality, compared to 30% in the placebo group, with significant differences measured by chi-square test (χ2(4) = 21.01, p = 0.0003), highlighting the effects due to Melissa officinalis L. No significant changes in physical activity or anxiety levels were observed.

CONCLUSIONS

these findings suggest that MOP may represent a natural and safe alternative to traditional pharmacological treatments for insomnia.

Neither fifty percent slow-wave sleep suppression nor fifty percent rapid eye movement sleep suppression does impair memory consolidation

Establishing well-defined relationships between sleep features and memory consolidation is essential in comprehending the pathophysiology of cognitive decline commonly seen in patients with insomnia, depression, and other sleep-disrupting conditions. Twenty-eight volunteers participated in two experimental sessions: a session with selective SWS suppression during one night and a session with undisturbed night sleep (as a control condition). Fifteen of them also participated in a third session with REM suppression. Suppression was achieved by presenting an acoustic tone. In the evening and the morning, the participants completed procedural and declarative memory tasks and the Psychomotor vigilance task (PVT). Heart rate variability analysis and salivary cortisol were used to control possible stress reactions to sleep interference. SWS and REM suppression led to more than 50 percent reduction in the amount of these stages. Neither vigilance nor memory consolidation was impaired after SWS or REM suppression. Unexpectedly, a beneficial effect of selective SWS suppression on PVT performance was found. Similarly, after a night with SWS suppression, the overnight improvement in procedural skills was higher than after a night with REM suppression and after a night with undisturbed sleep. Our data brings into question the extent to which SWS and REM are truly necessary for effective memory consolidation to proceed. Moreover, SWS suppression may even improve the performance of some tasks, possibly by reducing sleep inertia associated with undisturbed sleep.

Relation between sleep spindles and semantically induced false memory

BACKGROUND

Overnight sleep promotes memory consolidation, although few studies report no effect of sleep on memory. Previous studies suggest significant correlation between sleep dependent memory consolidation and spindle density. The present study is an attempt to understand the effects of sleep on false memories expressed as function of spindle density.

METHODS

Fifteen volunteers (all males) were tested on false memory paradigm using semantic associates across sleep and sleep deprivation experimental nights. Volunteers were tested on old/new recognition tests following a night of recovery sleep post experimental night.

RESULTS

The results suggest that the effects of sleep on false memories are not significantly different than those for true memories on old/new recognition test. The study results report difference in correlation between spindle density and true and false memories. False memories demonstrate slightly higher correlations with spindle densities in the right hemisphere.

CONCLUSION

We conclude that sleep effects on false memories are evident in sleep spindle densities and these effects are more pronounced over the right brain hemisphere.

Post-conditioning sleep deprivation facilitates delay and trace fear memory extinction

Trace and delay auditory fear conditioning involve different memory association strategies based on working memory involvement; however, their differences in long-term processing through sleep and extinction training remain unclear. While females often exhibit more persistent fear, complicating psychiatric treatment, most studies have primarily focused on how sleep affects initial recall in male mice. We investigated the three-way interaction between tests (trace vs. delay), sleep states, and sex during initial recall, extinction, and post-extinction remote recall. A six-hour post-conditioning sleep deprivation (SD) did not affect freezing behavior during the following day's extinction training of delay fear memory. However, during post-extinction remote recall of delay fear memory, SD prevented spontaneous recovery in males and reduced persistent freezing in females. In contrast, SD rapidly facilitated extinction of trace fear memory. In summary, SD enhances extinction both in the short-term and long-term, depending on the conditioning protocol. These findings highlight the importance of long-term assessments to explore interactions among emotional memory, sleep, and sex differences, with implications for individualized mechanisms underlying post-traumatic stress disorder (PTSD) and its treatments.

The influence of intentions on dream content

Study Objectives

The "Zeigarnik effect" refers to the phenomenon where future intentions are remembered effectively only as long as they are not executed. This study investigates whether these intentions, which remain active during sleep, influence dream content.

Methods

After an adaptation night, each of the 19 participants (10 women and 9 men) received three different task plans in the evening before the experimental night, each describing how to perform specific tasks. One of the task plans (completed) was then to be executed before the sleep period, another task (uncompleted) was told to be executed in the next morning, and on the third task (interrupted) participants were interrupted during the enactment before sleep and told to resume it the next morning. Polysomnography and multiple awakenings were conducted, resulting in 86 dream reports, 36 in NREM stage 2, and 50 in rapid eye movement sleep. After a traditional rating-based analysis of dream reports yielded inconsistent results, we analyzed the reports using a transformer-based assessment of dream incorporation, which quantified the semantic similarity between the dreams and pre-sleep tasks.

Results

The number of dreams showing above-criterion similarity to the respective task was significantly lower for the completed than the uncompleted or interrupted tasks (p < .05, χ2 test). This pattern was confirmed through a forced choice approach, where-based on the similarity of single sentences of the dream reports-each dream report was allocated to one of the three task plans (p < 0.01, one-tailed χ2 test).

Conclusions

Active intentions increase the likelihood of dream content being semantically similar to these intentions.

Offline hippocampal reactivation during dentate spikes supports flexible memory

Stabilizing new memories requires coordinated neuronal spiking activity during sleep. Hippocampal sharp-wave ripples (SWRs) in the cornu ammonis (CA) region and dentate spikes (DSs) in the dentate gyrus (DG) are prime candidate network events for supporting this offline process. SWRs have been studied extensively, but the contribution of DSs remains unclear. By combining triple-ensemble (DG-CA3-CA1) recordings and closed-loop optogenetics in mice, we show that, like SWRs, DSs synchronize spiking across DG and CA principal cells to reactivate population-level patterns of neuronal coactivity expressed during prior waking experience. Notably, the population coactivity structure in DSs is more diverse and higher dimensional than that seen during SWRs. Importantly, suppressing DG granule cell spiking selectively during DSs impairs subsequent flexible memory performance during multi-object recognition tasks and associated hippocampal patterns of neuronal coactivity. We conclude that DSs constitute a second offline network event central to hippocampal population dynamics serving memory-guided behavior.

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.

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.

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.

Isolated theta waves originating from the midline thalamus trigger memory reactivation during NREM sleep in mice

During non-rapid eye movement (NREM) sleep, neural ensembles in the entorhinal-hippocampal circuit responsible for encoding recent memories undergo reactivation to facilitate the process of memory consolidation. This reactivation is widely acknowledged as pivotal for the formation of stable memory and its impairment is closely associated with memory dysfunction. To date, the neural mechanisms driving the reactivation of neural ensembles during NREM sleep remain poorly understood. Here, we show that the neural ensembles in the medial entorhinal cortex (MEC) that encode spatial experiences exhibit reactivation during NREM sleep. Notably, this reactivation consistently coincides with isolated theta waves. In addition, we found that the nucleus reuniens (RE) in the midline thalamus exhibits typical theta waves during NREM sleep, which are highly synchronized with those occurring in the MEC in male mice. Closed-loop optogenetic inhibition of the RE-MEC pathway specifically suppressed these isolated theta waves, resulting in impaired reactivation and compromised memory consolidation following a spatial memory task in male mice. The findings suggest that theta waves originating from the ventral midline thalamus play a role in initiating memory reactivation and consolidation during sleep.

The human claustrum tracks slow waves during sleep

Slow waves are a distinguishing feature of non-rapid-eye-movement (NREM) sleep, an evolutionarily conserved process critical for brain function. Non-human studies suggest that the claustrum, a small subcortical nucleus, coordinates slow waves. We show that, in contrast to neurons from other brain regions, claustrum neurons in the human brain increase their spiking activity and track slow waves during NREM sleep, suggesting that the claustrum plays a role in coordinating human sleep architecture.

Contributions of Speaking, Listening, and Semantic Depth to Word Learning in Typical 3- and 4-Year-Olds

PURPOSE

This study examined learning via perception, learning via production, and semantic depth as contributors to word learning in preschool-aged children. There is broad evidence that semantic depth is an important contributor to word learning, especially when semantic cues are repeated and spaced out over time. Perceptual learning and production learning each support word learning sometimes, but not in all cases. The purpose of this study was to examine all three learning mechanisms within a single experimental paradigm.

METHOD

Thirty-six typically developing preschool children completed the experiment. They were familiarized with 16 novel words that were contextualized as alien names. These aliens came in four sets, each set comprising one base alien and three modified aliens marked by suffixes. Children completed four familiarizations: two in which they simply listened to the alien names (perceptual learning) and two where they repeated the alien names (production learning). Those conditions were crossed with a semantic depth manipulation (aliens with and without verbal semantic cues). Following each familiarization, referent identification and confrontation naming tasks were completed to assess learning.

RESULTS

Children were able to identify more alien referents following familiarizations with semantic depth. There were no significant effects of either perceptual learning or production learning.

CONCLUSIONS

This study confirms and expands on the benefits of semantic depth, but the results are unclear about the relative importance of perception and production to word learning. Nevertheless, the study suggests benefits to simultaneously studying multiple factors related to word learning.

Louis EK, McCarter SJ, Bukartyk J, Przybelski SA, Kamykowski MG, Spychalla AJ, Machulda MM, Boeve BF, Petersen RC, Jack CR, Lowe VJ, Graff-Radford J, Worrell GA, Somers VK, Varga AW, Vemuri P. Non-rapid eye movement sleep slow-wave activity features are associated with amyloid accumulation in older adults with obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is associated with an increased risk for cognitive impairment and dementia, which likely involves Alzheimer's disease pathology. Non-rapid eye movement slow-wave activity (SWA) has been implicated in amyloid clearance, but it has not been studied in the context of longitudinal amyloid accumulation in OSA. This longitudinal retrospective study aims to investigate the relationship between polysomnographic and electrophysiological SWA features and amyloid accumulation. From the Mayo Clinic Study of Aging cohort, we identified 71 participants ≥60 years old with OSA (mean baseline age = 72.9 ± 7.5 years, 60.6% male, 93% cognitively unimpaired) who had at least 2 consecutive Amyloid Pittsburgh Compound B (PiB)-PET scans and a polysomnographic study within 5 years of the baseline scan and before the second scan. Annualized PiB-PET accumulation [global ΔPiB(log)/year] was estimated by the difference between the second and first log-transformed global PiB-PET uptake estimations divided by the interval between scans (years). Sixty-four participants were included in SWA analysis. SWA was characterized by the mean relative spectral power density (%) in slow oscillation (SO: 0.5-0.9 Hz) and delta (1-3.9 Hz) frequency bands and by their downslopes (SO-slope and delta-slope, respectively) during the diagnostic portion of polysomnography. We fit linear regression models to test for associations among global ΔPiB(log)/year, SWA features (mean SO% and delta% or mean SO-slope and delta-slope), and OSA severity markers, after adjusting for age at baseline PiB-PET, APOE ɛ4 and baseline amyloid positivity. For 1 SD increase in SO% and SO-slope, global ΔPiB(log)/year increased by 0.0033 (95% CI: 0.0001; 0.0064, P = 0.042) and 0.0069 (95% CI: 0.0009; 0.0129, P = 0.026), which were comparable to 32% and 59% of the effect size associated with baseline amyloid positivity, respectively. Delta-slope was associated with a reduction in global ΔPiB(log)/year by -0.0082 (95% CI: -0.0143; -0.0021, P = 0.009). Sleep apnoea severity was not associated with amyloid accumulation. Regional associations were stronger in the pre-frontal region. Both slow-wave slopes had more significant and widespread regional associations. Annualized PiB-PET accumulation was positively associated with SO and SO-slope, which may reflect altered sleep homeostasis due to increased homeostatic pressure in the setting of unmet sleep needs, increased synaptic strength, and/or hyper-excitability in OSA. Delta-slope was inversely associated with PiB-PET accumulation, suggesting it may represent residual physiological activity. Further investigation of SWA dynamics in the presence of sleep disorders before and after treatment is necessary for understanding the relationship between amyloid accumulation and SWA physiology.

Alzheimer's disease and sleep disorders: A bidirectional relationship

Alzheimer's disease (AD) is the most prevalent dementia, pathologically featuring abnormal accumulation of amyloid-β (Aβ) and hyperphosphorylated tau, while sleep, divided into rapid eye movement sleep (REM) and nonrapid eye movement sleep (NREM), plays a key role in consolidating social and spatial memory. Emerging evidence has revealed that sleep disorders such as circadian disturbances and disruption of neuronal rhythm activity are considered as both candidate risks and consequence of AD, suggesting a bidirectional relationship between sleep and AD. This review will firstly grasp basic knowledge of AD pathogenesis, then highlight macrostructural and microstructural alteration of sleep along with AD progression, explain the interaction between accumulation of Aβ and hyperphosphorylated tau, which are two critical neuropathological processes of AD, as well as neuroinflammation and sleep, and finally introduce several methods of sleep enhancement as strategies to reduce AD-associated neuropathology. Although theories about the bidirectional relationship and relevant therapeutic methods in mice have been well developed in recent years, the knowledge in human is still limited. More studies on how to effectively ameliorate AD pathology in patients by sleep enhancement and what specific roles of sleep play in AD are needed.