Spared and impaired sleep-dependent memory consolidation in schizophrenia

Overview on cognitive impairment in psychotic disorders: From impaired microcircuits to dysconnectivity

Schizophrenia's cognitive deficits, often overshadowed by positive symptoms, significantly contribute to the disorder's morbidity. Increasing attention highlights these deficits as reflections of neural circuit dysfunction across various cortical regions. Numerous connectivity alterations linked to cognitive symptoms in psychotic disorders have been reported, both at the macroscopic and microscopic level, emphasizing the potential role of plasticity and microcircuits impairment during development and later stages. However, the heterogeneous clinical presentation of cognitive impairment and diverse connectivity findings pose challenges in summarizing them into a cohesive picture. This review aims to synthesize major cognitive alterations, recent insights into network structural and functional connectivity changes and proposed mechanisms and microcircuit alterations underpinning these symptoms, particularly focusing on neurodevelopmental impairment, E/I balance, and sleep disturbances. Finally, we will also comment on some of the most recent and promising therapeutic approaches that aim to target these mechanisms to address cognitive symptoms. Through this comprehensive exploration, we strive to provide an updated and nuanced overview of the multiscale connectivity impairment underlying cognitive impairment in psychotic disorders.

Sleep spindles as neurophysiological biomarkers of schizophrenia

Schizophrenia (SCZ) is a complex psychiatric disorder characterized by a wide range of clinical symptoms, including disrupted sleep. In recent years, there has been growing interest in assessing alterations in sleep parameters in patients with SCZ. Sleep spindles are brief (0.5-2 s) bursts of 12- to 16-Hz rhythmic electroencephalogram (EEG) oscillatory activity occurring during non-rapid eye movement (NREM) sleep. Spindles have been implicated in several critical brain functions, including learning, memory and plasticity, and are thought to reflect the integrity of underlying thalamocortical circuits. This review aims to provide an overview of the current research investigating sleep spindles in SCZ. After briefly describing the neurophysiological features of sleep spindles, I will discuss alterations in spindle characteristics observed in SCZ, their associations with the clinical symptomatology of these patients and their putative underlying neuronal and molecular mechanisms. I will then discuss the utility of sleep spindle measures as predictors of treatment response and disease progression. Finally, I will highlight future directions for research in this emerging field, including the prospect of utilizing sleep spindles as neurophysiological biomarkers of SCZ.

NREM sleep oscillations and their relations with sleep-dependent memory consolidation in early course psychosis and first-degree relatives

Sleep spindles are believed to mediate sleep-dependent memory consolidation, particularly when coupled to neocortical slow oscillations. Schizophrenia is characterized by a deficit in sleep spindles that correlates with reduced overnight memory consolidation. Here, we examined sleep spindle activity, slow oscillation-spindle coupling, and both motor procedural and verbal declarative memory consolidation in early course, minimally medicated psychosis patients and non-psychotic first-degree relatives. Using a four-night experimental procedure, we observed significant deficits in spindle density and amplitude in patients relative to controls that were driven by individuals with schizophrenia. Schizophrenia patients also showed reduced sleep-dependent consolidation of motor procedural memory, which correlated with spindle density. Contrary to expectations, there were no group differences in the consolidation of declarative memory on a word pairs task. Nor did the relatives of patients differ in spindle activity or memory consolidation compared with controls, however increased consistency in the timing of SO-spindle coupling were seen in both patient and relatives. Our results extend prior work by demonstrating correlated deficits in sleep spindles and sleep-dependent motor procedural memory consolidation in early course, minimally medicated patients with schizophrenia, but not in first-degree relatives. This is consistent with other work in suggesting that impaired sleep-dependent memory consolidation has some specificity for schizophrenia and is a core feature rather than reflecting the effects of medication or chronicity.

Sleep-dependent memory consolidation in schizophrenia: A systematic review and meta-analysis

Sleep disturbances and cognitive impairment are both persistent and common features of schizophrenia. Accumulating evidence indicates that sleep-dependent memory consolidation might be impaired in patients with schizophrenia compared to healthy controls. The current systematic review was performed in accordance with PRISMA guidelines. A random-effects model was used to calculate effect sizes (Hedge's g). In the quantitative review, three separate meta-analyses were conducted for procedural memory in healthy controls, schizophrenia, and comparison between healthy controls and schizophrenia. Additionally, separate meta-analyses were conducted for the studies using finger tapping motor sequence task, as it is the most commonly used task. The current systematic review included 14 studies including 304 patients with schizophrenia and 209 healthy controls. The random-effects model analyses for sleep-dependent procedural memory consolidation resulted in a small effect size in schizophrenia (g = 0.26), a large effect size in healthy controls (g = 0.98), a moderate effect size in healthy controls vs schizophrenia (g = 0.64). For the studies using finger tapping motor sequence task, meta-analyses resulted in a small effect size in schizophrenia (g = 0.19), a large effect size in healthy controls (g = 1.07), a moderate effect size in healthy controls vs schizophrenia (g = 0.70). In the qualitative review, there was also impaired sleep-dependent declarative memory consolidation in schizophrenia compared to healthy controls. Current findings support that sleep improves memory consolidation in healthy adults, but there is a deficit in sleep-dependent memory consolidation in people with schizophrenia. Future studies investigating sleep-dependent consolidation of different memory subtypes with polysomnography in different stages of psychotic disorders are needed.

Failure to consolidate statistical learning in developmental dyslexia

Statistical learning (SL), the ability to pick up patterns in sensory input, serves as one of the building blocks of language acquisition. Although SL has been studied extensively in developmental dyslexia (DD), much less is known about the way SL evolves over time. The handful of studies examining this question were all limited to the acquisition of motor sequential knowledge or highly learned segmented linguistic units. Here we examined memory consolidation of statistical regularities in adults with DD and typically developed (TD) readers by using auditory SL requiring the segmentation of units from continuous input, which represents one of the earliest learning challenges in language acquisition. DD and TD groups were exposed to tones in a probabilistically determined sequential structure varying in difficulty and subsequently tested for recognition of novel short sequences that adhered to this statistical pattern in immediate and delayed-recall sessions separated by a night of sleep. SL performance of the DD group at the easy and hard difficulty levels was poorer than that of the TD group in the immediate-recall session. Importantly, DD participants showed a significant overnight deterioration in SL performance at the medium difficulty level compared to TD, who instead showed overnight stabilization of the learned information. These findings imply that SL difficulties in DD may arise not only from impaired initial learning but also due to a failure to consolidate statistically structured information into long-term memory. We hypothesize that these deficits disrupt the typical course of language acquisition in those with DD.

Transient oscillation dynamics during sleep provide a robust basis for electroencephalographic phenotyping and biomarker identification

Transient oscillatory events in the sleep electroencephalogram represent short-term coordinated network activity. Of particular importance, sleep spindles are transient oscillatory events associated with memory consolidation, which are altered in aging and in several psychiatric and neurodegenerative disorders. Spindle identification, however, currently contains implicit assumptions derived from what waveforms were historically easiest to discern by eye, and has recently been shown to select only a high-amplitude subset of transient events. Moreover, spindle activity is typically averaged across a sleep stage, collapsing continuous dynamics into discrete states. What information can be gained by expanding our view of transient oscillatory events and their dynamics? In this paper, we develop a novel approach to electroencephalographic phenotyping, characterizing a generalized class of transient time-frequency events across a wide frequency range using continuous dynamics. We demonstrate that the complex temporal evolution of transient events during sleep is highly stereotyped when viewed as a function of slow oscillation power (an objective, continuous metric of depth-of-sleep) and phase (a correlate of cortical up/down states). This two-fold power-phase representation has large intersubject variability-even within healthy controls-yet strong night-to-night stability for individuals, suggesting a robust basis for phenotyping. As a clinical application, we then analyze patients with schizophrenia, confirming established spindle (12-15 Hz) deficits as well as identifying novel differences in transient non-rapid eye movement events in low-alpha (7-10 Hz) and theta (4-6 Hz) ranges. Overall, these results offer an expanded view of transient activity, describing a broad class of events with properties varying continuously across spatial, temporal, and phase-coupling dimensions.

Alterations of sleep oscillations in Alzheimer's disease: A potential role for GABAergic neurons in the cortex, hippocampus, and thalamus

Sleep abnormalities are widely reported in patients with Alzheimer's disease (AD) and are linked to cognitive impairments. Sleep abnormalities could be potential biomarkers to detect AD since they are often observed at the preclinical stage. Moreover, sleep could be a target for early intervention to prevent or slow AD progression. Thus, here we review changes in brain oscillations observed during sleep, their connection to AD pathophysiology and the role of specific brain circuits. Slow oscillations (0.1-1 Hz), sleep spindles (8-15 Hz) and their coupling during non-REM sleep are consistently reduced in studies of patients and in AD mouse models although the timing and magnitude of these alterations depends on the pathophysiological changes and the animal model studied. Changes in delta (1-4 Hz) activity are more variable. Animal studies suggest that hippocampal sharp-wave ripples (100-250 Hz) are also affected. Reductions in REM sleep amount and slower oscillations during REM are seen in patients but less consistently in animal models. Thus, changes in a variety of sleep oscillations could impact sleep-dependent memory consolidation or restorative functions of sleep. Recent mechanistic studies suggest that alterations in the activity of GABAergic neurons in the cortex, hippocampus and thalamic reticular nucleus mediate sleep oscillatory changes in AD and represent a potential target for intervention. Longitudinal studies of the timing of AD-related sleep abnormalities with respect to pathology and dysfunction of specific neural networks are needed to identify translationally relevant biomarkers and guide early intervention strategies to prevent or delay AD progression.

Multi-target derivatives of D2AAK1 as potential antipsychotics - the effect of the substitution in the indole moiety

Schizophrenia is a complex disease which is best treated with multi-target drugs, such as atypical antipsychotics. Previously, using structure-based virtual screening we found a virtual hit D2AAK1 with nanomolar affinity to dopamine and serotonin receptors important in schizophrenia pharmacotherapy. As a part of optimization campaign of D2AAK1 we obtained its 17 derivatives also displaying a multi-target profile. Selected compounds were tested against off-targets in schizophrenia, i.e. histamine H 1 receptor and muscarinic M 1 receptor and did not display considerable affinity to these receptors. Two most promising compounds were subjected to behavioral studies. These compounds decreased amphetamine-induced hyperactivity in mice which indicates their antipsychotic potential. The compounds did not interfere with the memory consolidation in mice as determined in the passive avoidance test. The favorable pharmacological profile of the compounds was rationalized using molecular modeling.

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

INTRODUCTION

Memory deficiency has been shown in schizophrenia patients, but results on the role of sleep parameters in overnight consolidation of associative verbal memory are still missing. Therefore, the aim of our study was to elucidate underlying processes of impaired sleep-related consolidation of associative word pairs in schizophrenia including standard sleep parameters as well as sleep spindle counts and spectral analysis.

METHODS

Eighteen stably medicated schizophrenia patients and 24 healthy age-matched controls performed an associative declarative memory task before and after polysomnographic recordings. Part of the participants expected verbal associative memory testing in the morning, while the others did not. Furthermore, participants filled in self-rating questionnaires of schizophrenia-typical experiences (Eppendorf Schizophrenia Inventory [ESI] and Psychotic Symptom Rating Scale).

RESULTS

Schizophrenia patients performed worse in verbal declarative memory in the evening as well as in overnight consolidation (morning compared to evening performance). While duration of slow-wave sleep was nearly comparable between groups, schizophrenia patients showed lower sleep spindle count, reduced delta power during slow-wave sleep, and reduced spindle power during the slow oscillation (SO) up-state. In healthy but not in schizophrenia patients, a linear relationship between overnight memory consolidation and slow-wave sleep duration as well as delta power was evident. No significant effect with respect to the expectation of memory retrieval was evident in our data. Additionally, we observed a negative linear relationship between total number of sleep spindles and ESI score in healthy participants.

DISCUSSION/CONCLUSION

As expected, schizophrenia patients showed deficient overnight verbal declarative memory consolidation as compared to healthy controls. Reduced sleep spindles, delta power, and spindle power during the SO up-state may link sleep and memory deficiency in schizophrenia. Additionally, the absence of a linear relationship between sleep-related memory consolidation and slow-wave sleep as well as delta power suggests further functional impairments in schizophrenia. Note that this conclusion is based on observational data. Future studies should investigate if stimulation of delta waves during sleep could improve memory performance and thereby quality of life in schizophrenia.

Examining the relationship between working memory consolidation and long-term consolidation

An emerging area of research is focused on the relationship between working memory and long-term memory and the likely overlap between these processes. Of particular interest is how some information first maintained in working memory is retained for longer periods and eventually preserved in long-term memory. The process of stabilizing transient memory representations for lasting retention is referred to as consolidation in both the working memory and long-term memory literature, although these have historically been viewed as independent constructs. The present review aims to investigate the relationship between working memory consolidation and long-term memory consolidation, which both have rich, but distinct, histories. This review provides an overview of the proposed models and neural mechanisms of both types of consolidation, as well as clinical findings related to consolidation and potential approaches for the manipulation of consolidation. Finally, two hypotheses are proposed to explain the relationship between working memory consolidation and long-term memory consolidation.

Longitudinal associations between sleep duration and cognitive function in the elderly population in China: A 10-year follow-up study from 2005 to 2014

OBJECTIVE

Sleep duration is increasingly recognized as an important determinant of cognitive function among elderly. However, longitudinal studies on the relationship between sleep duration and cognitive function in Chinese elderly are rare. We sought to investigate the longitudinal association between sleep duration and cognitive function in Chinese elderly during a 10-year follow-up.

METHOD

This longitudinal study analyzed 2148 elderly (the baseline including 43.16% aged 70%-79%, 23.79% aged 80 and over) who had participated in four waves of the Chinese Longitudinal Healthy Longevity Survey during 2005-2014. Cognitive function (including global functioning and cognitive domains) was assessed using the Chinese version of the Mini-Mental State Examination. Sleep duration was assessed via self-reports. Mixed model analysis was used to evaluate the association between sleep duration and cognitive function, adjusting for sociodemographic variables and risk factors for cognitive function.

RESULTS

There is an inverted U-shaped relationship between sleep duration and global cognition and cognitive domains, with the highest cognitive scores observed for sleep durations between 6 and 9 h and the curve shifting from smooth to steeper from 2005 to 2014. The regression model showed that long sleep duration (>9 h) is significantly associated with global cognition and four cognitive domains: orientation, attention and calculation, immediate recall and visual construction. Both long and short sleep durations are significantly associated with delayed recall and not significantly associated with category fluency, language or the ability to follow a three-stage command. The five cognitive domains related to sleep duration are the domains that exhibited a rapid rate of decline.

CONCLUSIONS

Sleep duration can be identified as a modifiable risk factor for cognitive decline, as long or short sleep duration is associated with the five cognitive domains that exhibit cognitive decline. These findings suggest the need for intervention measures to maintain healthy sleep durations among Chinese elderly people.

Sleep Abnormalities in Schizophrenia: State of the Art and Next Steps

Sleep disturbances are commonly observed in schizophrenia, including in chronic, early-course, and first-episode patients. This has generated considerable interest, both in clinical and research endeavors, in characterizing the relationship between disturbed sleep and schizophrenia. Sleep features can be objectively assessed with EEG recordings. Traditionally, EEG studies have focused on sleep architecture, which includes non-REM and REM sleep stages. More recently, numerous studies have investigated alterations in sleep-specific rhythms, including EEG oscillations, such as sleep spindles and slow waves, in individuals with schizophrenia compared with control subjects. In this article, the author reviews state-of-the-art evidence of disturbed sleep in schizophrenia, starting from the relationship between sleep disturbances and clinical symptoms. First, the author presents studies demonstrating abnormalities in sleep architecture and sleep-oscillatory rhythms in schizophrenia and related psychotic disorders, with an emphasis on recent work demonstrating sleep spindles and slow-wave deficits in early-course and first-episode schizophrenia. Next, the author shows how these sleep abnormalities relate to the cognitive impairments in patients diagnosed with schizophrenia and point to dysfunctions in underlying thalamocortical circuits, Ca+ channel activity, and GABA-glutamate neurotransmission. Finally, the author discusses some of the next steps needed to further establish the role of altered sleep in schizophrenia, including the need to investigate sleep abnormalities across the psychotic spectrum and to establish their relationship with circadian disturbances, which in turn will contribute to the development of novel sleep-informed treatment interventions.

N-(3-{4-[3-(trifluoromethyl)phenyl]piperazin-1-yl}propyl)-1H-indazole-3-carboxamide (D2AAK3) as a potential antipsychotic: In vitro, in silico and in vivo evaluation of a multi-target ligand

Schizophrenia is a mental illness of not adequately understood causes that is not satisfactorily enough treated by current antipsychotics. In search for novel potential antipsychotics we performed structure-based virtual screening aimed to identify new dopamine D₂ receptor antagonists. We found compound D2AAK3 with affinity to dopamine D₂ receptor of 115 nM. D2AAK3 possesses additional nanomolar or low micromolar affinity to D₁, D₃, 5-HT_1A, 5-HT_2A and 5-HT₇ receptors, which makes it a good hit for further development as a multifunctional ligand. The compound has also some affinity to M₁ and H₁ receptors. We used homology modeling, molecular docking and molecular dynamics to study interactions of D2AAK3 with its molecular targets at the molecular level. In behavioral studies D2AAK3 decreases amphetamine-induced hyperactivity (when compared to the amphetamine-treated group) measured as spontaneous locomotor activity in mice. In addition, passive avoidance test demonstrated that D2AAK3 improves memory consolidation after acute treatment in mice. Elevated plus maze tests indicated that D2AAK3 induces anxiogenic activity 30 min after acute treatment, whereas this effect has no longer been observed 60 min after administration of the studied compound in mice.

Focal Sleep Spindle Deficits Reveal Focal Thalamocortical Dysfunction and Predict Cognitive Deficits in Sleep Activated Developmental Epilepsy

Childhood epilepsy with centrotemporal spikes (CECTS) is the most common focal epilepsy syndrome, yet the cause of this disease remains unknown. Now recognized as a mild epileptic encephalopathy, children exhibit sleep-activated focal epileptiform discharges and cognitive difficulties during the active phase of the disease. The association between the abnormal electrophysiology and sleep suggests disruption to thalamocortical circuits. Thalamocortical circuit dysfunction resulting in pathologic epileptiform activity could hinder the production of sleep spindles, a brain rhythm essential for memory processes. Despite this pathophysiologic connection, the relationship between spindles and cognitive symptoms in epileptic encephalopathies has not been previously evaluated. A significant challenge limiting such work has been the poor performance of available automated spindle detection methods in the setting of sharp activities, such as epileptic spikes. Here, we validate a robust new method to accurately measure sleep spindles in patients with epilepsy. We then apply this detector to a prospective cohort of male and female children with CECTS with combined high-density EEGs during sleep and cognitive testing at varying time points of disease. We show that: (1) children have a transient, focal deficit in spindles during the symptomatic phase of disease; (2) spindle rate anticorrelates with spike rate; and (3) spindle rate, but not spike rate, predicts performance on cognitive tasks. These findings demonstrate focal thalamocortical circuit dysfunction and provide a pathophysiological explanation for the shared seizures and cognitive symptoms in CECTS. Further, this work identifies sleep spindles as a potential treatment target of cognitive dysfunction in this common epileptic encephalopathy.SIGNIFICANCE STATEMENT Childhood epilepsy with centrotemporal spikes is the most common idiopathic focal epilepsy syndrome, characterized by self-limited focal seizures and cognitive symptoms. Here, we provide the first evidence that focal thalamocortical circuit dysfunction underlies the shared seizures and cognitive dysfunction observed. In doing so, we identify sleep spindles as a mechanistic biomarker, and potential treatment target, of cognitive dysfunction in this common developmental epilepsy and provide a novel method to reliably quantify spindles in brain recordings from patients with epilepsy.

The effects of eszopiclone on sleep spindles and memory consolidation in schizophrenia: a randomized clinical trial

Sleep spindles, defining oscillations of stage 2 non-rapid eye movement sleep (N2), mediate memory consolidation. Schizophrenia is characterized by reduced spindle activity that correlates with impaired sleep-dependent memory consolidation. In a small, randomized, placebo-controlled pilot study of schizophrenia, eszopiclone (Lunesta®), a nonbenzodiazepine sedative hypnotic, increased N2 spindle density (number/minute) but did not significantly improve memory. This larger double-blind crossover study that included healthy controls investigated whether eszopiclone could both increase N2 spindle density and improve memory. Twenty-six medicated schizophrenia outpatients and 29 healthy controls were randomly assigned to have a placebo or eszopiclone (3 mg) sleep visit first. Each visit involved two consecutive nights of high density polysomnography with training on the Motor Sequence Task (MST) on the second night and testing the following morning. Patients showed a widespread reduction of spindle density and, in both groups, eszopiclone increased spindle density but failed to enhance sleep-dependent procedural memory consolidation. Follow-up analyses revealed that eszopiclone also affected cortical slow oscillations: it decreased their amplitude, increased their duration, and rendered their phase locking with spindles more variable. Regardless of group or visit, the density of coupled spindle-slow oscillation events predicted memory consolidation significantly better than spindle density alone, suggesting that they are a better biomarker of memory consolidation. In conclusion, sleep oscillations are promising targets for improving memory consolidation in schizophrenia, but enhancing spindles is not enough. Effective therapies also need to preserve or enhance cortical slow oscillations and their coordination with thalamic spindles, an interregional dialog that is necessary for sleep-dependent memory consolidation.

Sleep spindle and slow wave abnormalities in schizophrenia and other psychotic disorders: Recent findings and future directions

Sleep spindles and slow waves are the two main oscillatory activities occurring during NREM sleep. Slow waves are ∼1 Hz, high amplitude, negative-positive deflections that are primarily generated and coordinated within the cortex, whereas sleep spindles are 12-16 Hz, waxing and waning oscillations that are initiated within the thalamus and regulated by thalamo-cortical circuits. In healthy subjects, these oscillations are thought to be responsible for the restorative aspects of sleep and have been increasingly shown to be involved in learning, memory and plasticity. Furthermore, deficits in sleep spindles and, to lesser extent, slow waves have been reported in both chronic schizophrenia (SCZ) and early course psychosis patients. In this article, we will first describe sleep spindle and slow wave characteristics, including their putative functional roles in the healthy brain. We will then review electrophysiological, genetic, and cognitive studies demonstrating spindle and slow wave impairments in SCZ and other psychotic disorders, with particularly emphasis on recent findings in early course patients. Finally, we will discuss how future work, including sleep studies in individuals at clinical high risk for psychosis, may help position spindles and slow waves as candidate biomarkers, as well as novel treatment targets, for SCZ and related psychotic disorders.

Reduced sleep spindle density in adolescent patients with early-onset schizophrenia compared to major depressive disorder and healthy controls

OBJECTIVES

During adolescence schizophrenia and major depressive disorder (MDD) increasingly emerge. Overlapping symptomatology during first presentation challenges the diagnostic process. Reduced sleep spindle density (SSD) was suggested as a biomarker in adults, discerning patients with schizophrenia from patients with depression or healthy controls (HC). We aimed to compare SSD in early-onset schizophrenia (EOS), with MDD, and HC, and to analyse associations of SSD with symptomatology and neurocognitive measures.

METHODS

Automatic sleep spindle detection was performed on all-night high-density EEG (128 electrodes) data of 12 EOS, 19 MDD, and 57 HC (age range 9.8-19), allowing an age- and sex-matching of 1:2 (patients vs. HC). Severity of current symptoms and neurocognitive variables were assessed in all patients.

RESULTS

SSD was defined between 13.75 and 14.50 Hz as within this frequency range SSD differed between EOS vs. HC in bin by bin analyses (12-15 Hz). In EOS, SSD was lower over 27 centro-temporal electrodes compared to HC and over 9 central electrodes compared to MDD. Reduced SSD in EOS compared to MDD and HC was accompanied by a high variability of SSD in all adolescents. SSD did not differ between MDD and HC. In the pooled sample of patients, lower SSD was associated with more severe Positive and Negative Symptoms Scale total score, more impaired memory consolidation and processing speed.

CONCLUSION

A high variability of SSD in all adolescents may reflect the evolving character of SSD. The association of reduced SSD with the symptom dimension of impaired cognition cuts across diagnostical entities.

Effects of a patient-derived de novo coding alteration of CACNA1I in mice connect a schizophrenia risk gene with sleep spindle deficits

CACNA1I, a schizophrenia risk gene, encodes a subtype of voltage-gated T-type calcium channel CaV3.3. We previously reported that a patient-derived missense de novo mutation (R1346H) of CACNA1I impaired CaV3.3 channel function. Here, we generated CaV3.3-RH knock-in animals, along with mice lacking CaV3.3, to investigate the biological impact of R1346H (RH) variation. We found that RH mutation altered cellular excitability in the thalamic reticular nucleus (TRN), where CaV3.3 is abundantly expressed. Moreover, RH mutation produced marked deficits in sleep spindle occurrence and morphology throughout non-rapid eye movement (NREM) sleep, while CaV3.3 haploinsufficiency gave rise to largely normal spindles. Therefore, mice harboring the RH mutation provide a patient derived genetic model not only to dissect the spindle biology but also to evaluate the effects of pharmacological reagents in normalizing sleep spindle deficits. Importantly, our analyses highlighted the significance of characterizing individual spindles and strengthen the inferences we can make across species over sleep spindles. In conclusion, this study established a translational link between a genetic allele and spindle deficits during NREM observed in schizophrenia patients, representing a key step toward testing the hypothesis that normalizing spindles may be beneficial for schizophrenia patients.

Sleep quality is related to brain glutamate and symptom severity in schizophrenia

Up to 80% of patients with schizophrenia experience sleep disturbances, which negatively impact daytime functioning. Given that the glutamatergic system is involved in the pathophysiology of schizophrenia as well as normal sleep-wake neurobiology, the current project aimed to determine whether sleep quality was related to brain glutamate levels in schizophrenia. The Pittsburgh Sleep Quality Index (PSQI) was used to assess subjective sleep quality and proton magnetic resonance spectroscopy (MRS) was used to quantify glutamate in the bilateral anterior cingulate, left parietal cortex, and left hippocampus. Results indicate that global PSQI scores were negatively correlated with the anterior cingulate and parietal glutamate levels. In patients with schizophrenia, poorer sleep quality correlated with greater positive symptom severity. Our findings suggest that poor sleep quality is related to greater positive symptom severity and lower levels of anterior cingulate glutamate in individuals with schizophrenia. Interventions to enhance sleep quality may prove beneficial for patients. Future studies will examine whether glutamate relates to objective measures of sleep quality, and whether glutamate may mediate the relationship between sleep quality and symptom severity across the schizophrenia-spectrum.

Sleep disturbances in schizophrenia: what we know, what still needs to be done

Sleep disturbances are commonly observed in schizophrenia (SCZ) and are associated with worse psychotic symptoms and poorer clinical outcomes. Early polysomnography studies have focused on characterizing differences in sleep architecture between patients with SCZ and healthy controls. More recently, research has focused on sleep-specific EEG oscillations, such as sleep spindles and slow waves, which reflect the integrity of underlying thalamo-cortical networks. Furthermore, high-density (hd)-EEG (≥64 channels), which affords enhanced spatial resolution, has been employed to better localize abnormalities in sleep characteristics and related thalamo-cortical circuits in patients with SCZ and related disorders. In this article, we will review the most relevant sleep abnormalities reported in SCZ, with an emphasis on recent findings, and propose directions for future research.

Abnormal Sleep Spindles, Memory Consolidation, and Schizophrenia

There is overwhelming evidence that sleep is crucial for memory consolidation. Patients with schizophrenia and their unaffected relatives have a specific deficit in sleep spindles, a defining oscillation of non-rapid eye movement (NREM) Stage 2 sleep that, in coordination with other NREM oscillations, mediate memory consolidation. In schizophrenia, the spindle deficit correlates with impaired sleep-dependent memory consolidation, positive symptoms, and abnormal thalamocortical connectivity. These relations point to dysfunction of the thalamic reticular nucleus (TRN), which generates spindles, gates the relay of sensory information to the cortex, and modulates thalamocortical communication. Genetic studies are beginning to provide clues to possible neurodevelopmental origins of TRN-mediated thalamocortical circuit dysfunction and to identify novel targets for treating the related memory deficits and symptoms. By forging empirical links in causal chains from risk genes to thalamocortical circuit dysfunction, spindle deficits, memory impairment, symptoms, and diagnosis, future research can advance our mechanistic understanding, treatment, and prevention of schizophrenia.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABA_A), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.