Two features of sleep slow waves: homeostatic and reactive aspects – from long term to instant sleep homeostasis

Neurophysiological features of dream recall and the phenomenology of dreams: Auditory stimulation impacts dream experiences

Studies on the electrophysiological and phenomenological aspects of dream experiences provide insight on consciousness during sleep. Whole night polysomnography (PSG) studies were conducted among 29 healthy young participants with high dream recall abilities. Dreams reports were collected during the second night by multiple awakening protocol. On the third night, participants were presented with an audiovisual task and during subsequent sleep, dream reports were collected following an auditory stimuli presentation. REM sleep dreams favor high dream recall rates when compared to N2 dreams. Enhanced EEG beta activity, functional connectivity across the brain structures of the default mode network (DMN) and activation of medial frontal cortex were observed during dream recall irrespective of the sleep states. Auditory stimulations influenced emotional dream experiences highlighting the possibility of target memory reactivation. The study highlights the potential role of dream states and dream experiences in understanding consciousness during sleep.

Heartbeat-related activity in the anterior thalamus differs between phasic and tonic REM sleep

Rapid eye movement (REM) sleep is a fundamental sleep state associated with diverse functions from elemental physiological processes to higher order neurocognitive functions. A growing body of research indicates that REM sleep with eye movements (phasic REM) differs from REM periods without ocular activity (tonic) in terms of spontaneous and evoked neural responses. Studies using auditory stimulation consistently observed enhanced evoked responses in tonic versus phasic REM, indicating that external processing is largely diminished when the eyes move during REM sleep. Whereas exteroceptive processing during sleep is widely studied, investigations on interoception (the processing of bodily signals) during sleep are scarce, and limited to scalp electroencephalographic recordings. Here we studied interoceptive processing in a group of epileptic patients (N = 11) by measuring their heartbeat-related neural activity in the anterior nuclei of the thalamus (ANT) during phasic and tonic REM sleep and resting wakefulness. Evoked potentials and beta-low gamma spectral power locked to the heartbeat were significantly different in phasic REM compared with tonic REM and wakefulness. Heartbeat-related neural signals exhibited pronounced inter-trial phase synchronization at lower (7-20 Hz) oscillatory activity in all vigilance states, but reduced gamma synchronization at later time points in phasic REM only. Tonic REM and wakefulness did not show significant differences in heartbeat-related activity in the ANT. Our findings indicate that heartbeat-related neural activity is detectable at the level of the ANT, showing distinct signatures of interoceptive processing in phasic REM compared with tonic REM and wakefulness. KEY POINTS: We studied interoceptive processing in the anterior the thalamus (ANT). The ANT tracks cardiac signals during wakefulness and rapid eye movement (REM) sleep. Phasic REM shows distinct patterns of heartbeat-related oscillatory activity. Interoceptive processing might be attenuated during REM periods with eye movements.

Slow-wave sleep is associated with nucleus accumbens volume in elderly adults

Slow-wave sleep (SWS) is essential for restorative neural processes and its decline is associated with both healthy and pathological ageing. Building on previous rodent research, this longitudinal study identified a significant association between nucleus accumbens (NAcc) volume and SWS duration in cognitively unimpaired older adults, whilst no significant link was observed between NAcc volume and N2 or rapid eye movement (REM) sleep percentage. Our findings support the involvement of the NAcc in ageing-related modulation of SWS and thus suggest the NAcc as a potential neural marker or therapeutic target for improving SWS.

K-Complex morphological alterations in insomnia disorder and their relationship with sleep state misperception

Insomnia disorder (ID) is characterized by electroencephalographic indexes of hyperarousal, often associated with the underestimation of sleep duration (i.e. sleep state misperception). Albeit non-rapid eye movement sleep K-complexes (KCs) are involved in sleep protection and arousal, only a few studies investigated their alterations in ID with heterogenous findings, and results about their possible relationship with sleep state misperception are missing. The study aims to assess KCs in ID and their relationship with sleep state misperception, also considering their correlation with sleep architecture (i.e. the large-scale organization of sleep). Nineteen ID patients (12 F; age: 42.4 ± 12.1 years) and 18 healthy controls (HC; 10 F; age: 41.6 ± 11.9 years) underwent a night of home polysomnography and completed sleep diaries upon awakening. KC density, amplitude, and area under the curve were assessed in midline frontal, central, and parietal derivations. Sleep state misperception was investigated by considering polysomnographic and subjective total sleep time (TST). We found reduced anterior KC morphology (i.e. amplitude and area under the curve) in ID patients compared to HCs, which was associated with TST underestimation. KC morphology was negatively associated with N3 latency, sleep fragmentation and arousal indexes, and positively related with N3 percentage and sleep efficiency. Our findings suggest an impaired sleep protection mechanism expressed by altered KCs morphology in ID involved in sleep state misperception. The observed correlations support the view of KC as the forerunner of slow-wave sleep and protector of sleep continuity. A better understanding of sleep-protecting mechanisms alteration as a predisposing and/or maintaining factor of ID is needed.

Cyclic Alternating EEG Patterns: From Sleep to Encephalopathy

SUMMARY

In the 2021 version of the Standardized Critical Care EEG Terminology, the American Clinical Neurophysiology Society introduced new definitions, including for the cyclic alternating pattern of encephalopathy (CAPE). CAPE refers to changes in background EEG activity, with two patterns alternating spontaneously in a regular manner. CAPE shares remarkable similarities with the cyclic alternating pattern, a natural EEG phenomenon occurring in normal non-rapid eye movement sleep, considered the main electrophysiological biomarker of sleep instability. This review explores similarities and differences between cyclic alternating pattern and CAPE and, leveraging the existing expertise on cyclic alternating pattern, aims to extend knowledge on CAPE. A standardized assessment of CAPE features is key to ascertain its prevalence and clinical significance among critically ill patients and to encompass the impact of confounding factors such as anesthetic and sedative agents. Although the preservation of non-rapid eye movement sleep-related elements has a well-known prognostic value in the critical care setting, the clinical importance of cyclic oscillating patterns and the prognostic significance of CAPE remain to be elucidated.

Changes in electroencephalographic microstates between evening and morning are associated with overnight sleep slow waves in healthy individuals

STUDY OBJECTIVES

Microstates are semi-stable voltage topographies that account for most of electroencephalogram (EEG) variance. However, the impact of time of the day and sleep on microstates has not been examined. To address this gap, we assessed whether microstates differed between the evening and morning and whether sleep slow waves correlated with microstate changes in healthy participants.

METHODS

Forty-five healthy participants were recruited. Each participant underwent 6 minutes of resting state EEG recordings in the evening and morning, interleaved by sleep EEGs. Evening-to-morning changes in microstate duration, coverage, and occurrence were assessed. Furthermore, correlation between microstate changes and sleep slow-wave activity (SWA) and slow-wave density (SWD) were performed.

RESULTS

Two-way ANOVAs with microstate class (A, B, C, and D) and time (evening and morning) revealed significant microstate class × time interaction for duration (F(44) = 5.571, p = 0.002), coverage (F(44) = 6.833, p = 0.001), and occurrence (F(44) = 5.715, p = 0.002). Post hoc comparisons showed significant effects for microstate C duration (padj = 0.048, Cohen's d = -0.389), coverage (padj = 0.002, Cohen's d = -0.580), and occurrence (padj = 0.002, Cohen's d = -0.606). Topographic analyses revealed inverse correlations between SWD, but not SWA, and evening-to-morning changes in microstate C duration (r = -0.51, padj = 0.002), coverage (r = -0.45, padj = 0.006), and occurrence (r = -0.38, padj = 0.033).

CONCLUSIONS

Microstate characteristics showed significant evening-to-morning changes associated with, and possibly regulated by, sleep slow waves. These findings suggest that future microstate studies should control for time of day and sleep effects.

Polysomnographic findings of myotonic dystrophy type 1/type 2: evidence from case-control studies

STUDY OBJECTIVES

This study explores polysomnographic and multiple sleep latency test (MSLT) differences between myotonic dystrophy type 1/type 2 (DM1/DM2) patients and controls.

METHODS

An electronic literature search was conducted in MEDLINE, EMBASE, All EBM databases, and Web of Science from inception to Aug 2023.

RESULTS

Meta-analyses revealed significant reductions in sleep efficiency, N2 percentage, mean SpO2, and MSLT measured mean sleep latency, and increases in N3 sleep, wake time after sleep onset, apnea hypopnea index, and periodic limb movement index in DM1 patients compared with controls. However, any differences of polysomnographic sleep change between DM2 patients and controls could not be established due to limited available studies.

CONCLUSIONS

Multiple significant polysomnographic abnormalities are present in DM1. More case-control studies evaluating polysomnographic changes in DM2 compared with controls are needed.

[The role of cerebral activation in the sleep-wake cycle]

The development of views on cerebral activation in the wakefulness-sleep cycle, starting with the work of Constantin von Economo, is considered. The emphasis is on the cyclic activation of high-amplitude discharges in sleep, which, with known assumptions, can include K-complexes, as well as patterns of delta-like waves. Considering the participation of the peripheral nervous system in this, the integrative role of cyclic activation of high-amplitude discharges in the organization of the sleep-wake cycle is discussed.

A simple and fast ANN-based method of studying slow-wave sleep microstructure in freely moving rats

Electroencephalography (EEG) is a common technique for measuring brain activity. Artificial Neuronal Networks (ANNs) can provide valuable insights into the brain dynamics of humans and animals. We built a simple and fast shallow ANN-based solution for sleep recognition in EEGs recorded in freely moving rats. The ANN was constructed using open-source software and truncated to one formula with empirically defined weight coefficients. The optimization of the ANN model's performance (i.e., post-processing) relied on a probability-related approach to sleep microstructure. This approach could be a good way to analyze large datasets. In the current dataset, the slow-wave sleep was recognized with the sensitivity of 0.91 and the specificity of 0.98. The optimal model performance achieved with minimum sleep duration of 80-90 s and sleep interruption of 14-18 s. Our results suggest the following fundamental issues. First, 14-18 s sleep interruptions might be the archetypal micro-arousals in rats. Second, slow-wave sleep in rats might be built up of a set of sleep "building blocks" lasting 80-90 s.

Criticality of neuronal avalanches in human sleep and their relationship with sleep macro- and micro-architecture

Sleep plays a key role in preserving brain function, keeping brain networks in a state that ensures optimal computation. Empirical evidence indicates that this state is consistent with criticality, where scale-free neuronal avalanches emerge. However, the connection between sleep architecture and brain tuning to criticality remains poorly understood. Here, we characterize the critical behavior of avalanches and study their relationship with sleep macro- and micro-architectures, in particular, the cyclic alternating pattern (CAP). We show that avalanches exhibit robust scaling behaviors, with exponents obeying scaling relations consistent with the mean-field directed percolation universality class. We demonstrate that avalanche dynamics is modulated by the NREM-REM cycles and that, within NREM sleep, avalanche occurrence correlates with CAP activation phases-indicating a potential link between CAP and brain tuning to criticality. The results open new perspectives on the collective dynamics underlying CAP function, and on the relationship between sleep architecture, avalanches, and self-organization to criticality.

The Metabotropic Glutamate 5 Receptor in Sleep and Wakefulness: Focus on the Cortico-Thalamo-Cortical Oscillations

Sleep is an essential innate but complex behaviour which is ubiquitous in the animal kingdom. Our knowledge of the distinct neural circuit mechanisms that regulate sleep and wake states in the brain are, however, still limited. It is therefore important to understand how these circuits operate during health and disease. This review will highlight the function of mGlu5 receptors within the thalamocortical circuitry in physiological and pathological sleep states. We will also evaluate the potential of targeting mGlu5 receptors as a therapeutic strategy for sleep disorders that often co-occur with epileptic seizures.

The Contribution of Sleep Texture in the Characterization of Sleep Apnea

Obstructive sleep apnea (OSA) is multi-faceted world-wide-distributed disorder exerting deep effects on the sleeping brain. In the latest years, strong efforts have been dedicated to finding novel measures assessing the real impact and severity of the pathology, traditionally trivialized by the simplistic apnea/hypopnea index. Due to the unavoidable connection between OSA and sleep, we reviewed the key aspects linking the breathing disorder with sleep pathophysiology, focusing on the role of cyclic alternating pattern (CAP). Sleep structure, reflecting the degree of apnea-induced sleep instability, may provide topical information to stratify OSA severity and foresee some of its dangerous consequences such as excessive daytime sleepiness and cognitive deterioration. Machine learning approaches may reinforce our understanding of this complex multi-level pathology, supporting patients' phenotypization and easing in a more tailored approach for sleep apnea.

Lateralized tactile stimulation during NREM sleep globally increases both slow and fast frequency activities

Slow frequency activity during non-rapid eye movement (NREM) sleep emerges from synchronized activity of widely distributed thalamo-cortical and cortico-cortical networks, reflecting homeostatic and restorative properties of sleep. Slow frequency activity exhibits a reactive nature, and can be increased by acoustic stimulation. Although non-invasive brain stimulation is a promising technique in basic and clinical sleep research, sensory stimulation studies focusing on modalities other than the acoustic are scarce. We explored here the potential of lateralized vibro-tactile stimulation (VTS) of the finger to locally modify electroencephalographic activity during nocturnal NREM sleep. Eight seconds-long sequences of vibro-tactile pulses were delivered at a rate of 1 Hz either to the left or to the right index finger, in addition to a sham condition, in fourteen healthy participants. VTS markedly increased slow frequency activity that peaked between 1-4 Hz but extended to higher (~13 Hz) frequencies, with fronto-central dominance. Enhanced slow frequency activity was accompanied by increased (14-22 Hz) fast frequency power peaking over central and posterior locations. VTS increased the amplitude of slow waves, especially during the first 3-4 s of stimulation. Noticeably, we did not observe local-hemispheric effects, that is, VTS resulted in a global cortical response regardless of stimulation laterality. VTS moderately increased slow and fast frequency activities in resting wakefulness, to a much lower extent compared to NREM sleep. The concomitant increase in slow and fast frequency activities in response to VTS indicates an instant homeostatic response coupled with wake-like, high-frequency activity potentially reflecting transient periods of increased environmental processing.

The effect of ketamine on delta-range coupling between prefrontal cortex and hippocampus supported by respiratory rhythmic input from the olfactory bulb

Respiratory rhythm plays an important role in cognitive functions in rodents, as well as in humans. Respiratory related oscillation (RRO), generated in the olfactory bulb (OB), is an extrinsic rhythm imposed on brain networks. In rats, RRO can couple with intrinsic brain oscillations at theta frequency during sniffing and in the delta range outside of such episodes. Disruption of gamma synchronization in cortical networks by ketamine is well established whereas its effects on slow rhythms are poorly understood. We found in this study, that RRO in prefrontal cortex (PFC) and hippocampus (HC) remains present after ketamine injection, even on the background of highly unstable respiratory rate, co-incident with "psychotic-like" behavior and abnormal cortical gamma activity. Guided by the timing of ketamine-induced gamma reaction, pairwise coherences between structures exhibiting RRO and their correlation structure was statistically tested in 5-min segments post-injection (0-25 min) and during recovery (1, 5, 10 h). As in control, RRO in the OB was firmly followed by cortical-bound OB exits directed toward PFC but not to HC. RRO between these structures, however, significantly correlated with OB-HC but not with OB-PFC. The only exception to this general observation was observed during a short transitional period, immediately after injection. Ketamine has a remarkable history in psychiatric research. Modeling chronic NMDA-hypofunction using acute NMDA-receptor blockade shifted the primary focus of schizophrenia research to dysfunctional cortical microcircuitry and the recent discovery of ketamine's antidepressant actions extended investigations to neurophysiology of anxiety and depression. Cortical oscillations are relevant for understanding their pathomechanism.

Non-rapid eye movement sleep instability in adults with epilepsy: a systematic review and meta-analysis of cyclic alternating pattern

STUDY OBJECTIVES

Epilepsy is characterized by disrupted sleep architecture. Studies on sleep macro- and microstructure revealed that patients with epilepsy experience disturbed rapid eye movement (REM) sleep; however, no consensus has been reached on non-REM (NREM) sleep changes. Cyclic alternating pattern (CAP) is a marker of sleep instability that occurs only during NREM sleep. This meta-analysis investigated CAP differences between patients with epilepsy and healthy controls.

METHODS

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines in searching PubMed, Embase, and Cochrane Central database for studies comparing polysomnographic sleep microstructures between patients with epilepsy and healthy controls. A meta-analysis using a random-effects model was performed. We compared CAP rates, percentages of phase A1, A2, A3 subtypes, and phase B durations between patients with epilepsy and healthy controls.

RESULTS

A total of 11 studies, including 209 patients with epilepsy and 197 healthy controls, fulfilled the eligibility criteria. Compared with healthy controls, patients with epilepsy had significantly increased CAP rates and decreased A1 subtype percentages, and patients with sleep-related epilepsy had increased A3 subtype percentages. Subgroup analyses revealed that antiseizure medications (ASMs) decreased CAP rates and increased phase B durations but did not affect the microstates of phase A in patients with sleep-related epilepsy.

CONCLUSIONS

This meta-analysis detected statistically significant differences in CAP parameters between patients with epilepsy and healthy controls. Our findings suggest patients with epilepsy experience NREM sleep instability. ASMs treatment may decrease NREM instability but did not alter the microstates of phase A.

Disorders of arousal and sleep-related hypermotor epilepsy - overview and challenges night is a battlefield of sleep and arousal promoting forces

Arousability and reactivity to sensory stimuli are essential features of sleep, discriminating it from coma and keeping the sleeper in contact with the environment. Arousals and oscillations during sleep serve the reversibility of sleep and carry an alarm function awakening the sleeper in danger. In this review, we will explore mechanisms and circuits involved in arousal intrusions within the sleep texture, focusing on the significance of these phenomena in two sleep-related conditions: NREM sleep parasomnias and sleep-related hypermotor epilepsy. Knowledges and gaps in the field are discussed.

Sleep and homeostatic control of plasticity

Sleep homeostasis is a complex neurobiologic phenomenon involving a number of molecular pathways, neurotransmitter release, synaptic activity, and factors modulating neural networks. Sleep plasticity allows for homeostatic optimization of neural networks and the replay-based consolidation of specific circuits, especially important for cognition, behavior, and information processing. Furthermore, research is currently moving from an essentially brain-focused to a more comprehensive view involving other systems, such as the immune system, hormonal status, and metabolic pathways. When dysfunctional, these systems contribute to sleep loss and fragmentation as well as to sleep need. In this chapter, the implications of neural plasticity and sleep homeostasis for the diagnosis and treatment of some major sleep disorders, such as insomnia and sleep deprivation, obstructive sleep apnea syndrome, restless legs syndrome, REM sleep behavior disorder, and narcolepsy are discussed in detail with their therapeutical implications. This chapter highlights that sleep is necessary for the maintenance of an optimal brain function and is sensitive to both genetic background and environmental enrichment. Even in pathologic conditions, sleep acts as a resilient plastic state that consolidates prior information and prioritizes network activity for efficient brain functioning.

Sleep and brain evolution across the human lifespan: A mutual embrace

Sleep can be considered a window to ascertain brain wellness: it dynamically changes with brain maturation and can even indicate the occurrence of concealed pathological processes. Starting from prenatal life, brain and sleep undergo an impressive developmental journey that accompanies human life throughout all its steps. A complex mutual influence rules this fascinating course and cannot be ignored while analysing its evolution. Basic knowledge on the significance and evolution of brain and sleep ontogenesis can improve the clinical understanding of patient's wellbeing in a more holistic perspective. In this review we summarized the main notions on the intermingled relationship between sleep and brain evolutionary processes across human lifespan, with a focus on sleep microstructure dynamics.

Sleep Disturbances in Rats With Genetic Pre-disposition to Spike-Wave Epilepsy (WAG/Rij)

Wistar Albino Glaxo Rijswijk (WAG/Rij) rats are widely used in basic and pre-clinical studies as a valid genetic model of absence epilepsy. Adult WAG/Rij rats exhibit generalized 8–10-Hz spike-wave discharges (SWDs) in the electroencephalogram. SWDs are known to result from thalamocortical circuit dysfunction, and this implies an intimate relationship between slow-wave EEG activity, sleep spindles, and SWDs. The present mini review summarizes relevant research on sleep-related disturbances associated with spike-wave epilepsy in WAG/Rij rats in the domain of slow-wave sleep EEG and microarousals. It also discusses enhancement of the intermediate stage of sleep. In general, sleep EEG studies provide important information about epileptogenic processes related to spike-wave epilepsy.

Cyclic Alternating Pattern Analysis in Periodic Leg Movements in Sleep in Patients With Obstructive Sleep Apnea Syndrome Before and After Positive Airway Pressure Treatment

PURPOSE

Cyclic alternating pattern (CAP) is known to increase in many conditions of sleep disruption and sleep disorders, including obstructive sleep apnea syndrome and periodic limb movements in sleep (PLMS). Periodic limb movements in sleep associated with obstructive sleep apnea syndrome may vanish after positive airway pressure treatment, may persist, or emerge at treatment night. Here, the authors aimed to investigate the underlying pathophysiology of nonvanishing, vanishing, or newly emergent PLMS.

METHODS

The authors designed a prospective study and included 10 patients with nonvanishing PLMS during positive airway pressure therapy, 10 patients with vanishing PLMS, 10 patients with newly emergent PLMS, and 10 patients without PLMS at both nights. The CAP analysis was performed in detail at diagnostic polysomnography recording and at positive airway pressure titration. The changes in CAP parameters were evaluated in regard to nonvanishing, vanishing, or newly emergent PLMS.

RESULTS

Periodic limb movements in sleep related to A1 subtype of CAP were observed to decrease under positive airway pressure titration more than PLMS related to A3 subtype of CAP. The A3 subtype of CAP was higher in patients with vanishing PLMS than those with newly emergent PLMS. The newly emergent PLMS were mostly related to A1 subtype of CAP compared with A3 subtype of CAP.

CONCLUSIONS

This study showed that vanishing, nonvanishing, or newly emerging PLMS may indeed represent different underlying pathophysiology. The authors suggest that organization of sleep and preservation of ultradian rhythms during titration may determine whether PLMS will be vanished or persist. Newly emergent PLMS may probably arise from a separate central generator by the activation of higher cortical areas.

Susceptibility to auditory closed-loop stimulation of sleep slow oscillations changes with age

Study Objectives

Cortical slow oscillations (SOs) and thalamocortical sleep spindles hallmark slow wave sleep and facilitate memory consolidation, both of which are reduced with age. Experiments utilizing auditory closed-loop stimulation to enhance these oscillations showed great potential in young and older subjects. However, the magnitude of responses has yet to be compared between these age groups. We examined the possibility of enhancing SOs and performance on different memory tasks in a healthy middle-aged population using this stimulation and contrast effects to younger adults.

Methods

In a within-subject design, 17 subjects (55.7 ± 1.0 years) received auditory stimulation in synchrony with SO up-states, which was compared to a no-stimulation sham condition. Overnight memory consolidation was assessed for declarative word-pairs and procedural finger-tapping skill. Post-sleep encoding capabilities were tested with a picture recognition task. Electrophysiological effects of stimulation were compared to a previous younger cohort (n = 11, 24.2 ± 0.9 years).

Results

Overnight retention and post-sleep encoding performance of the older cohort revealed no beneficial effect of stimulation, which contrasts with the enhancing effect the same stimulation protocol had in our younger cohort. Auditory stimulation prolonged endogenous SO trains and induced sleep spindles phase-locked to SO up-states in the older population. However, responses were markedly reduced compared to younger subjects. Additionally, the temporal dynamics of stimulation effects on SOs and spindles differed between age groups.

Conclusions

Our findings suggest that the susceptibility to auditory stimulation during sleep drastically changes with age and reveal the difficulties of translating a functional protocol from younger to older populations.

K-complexes are a sensitive marker of noise-related sensory processing during sleep: A pilot study

STUDY OBJECTIVES

The primary aim of this study was to examine dose-response relationships between sound pressure levels (SPLs) and K-complex occurrence probability for wind farm and road traffic noise. A secondary aim was to compare K-complex dose-responses to manually scored EEG arousals and awakenings.

METHODS

Twenty-five participants underwent polysomnography recordings and noise exposure during sleep in a laboratory. Wind farm and road traffic noise recordings of 20-sec duration were played in random order at 6 SPLs between 33 - 48 dBA during established N2 or deeper sleep. Noise periods were separated with periods of 23 dBA background noise. K-complexes were scored using a validated algorithm. K-complex occurrence probability was compared between noise types controlling for noise SPL, subjective noise sensitivity and measured hearing acuity.

RESULTS

Noise-induced K-complexes were observed in N2 sleep at SPLs as low as 33 dBA (Odds ratio, 33dBA vs 23 dBA, mean (95% confidence interval); 1.75 (1.16, 2.66)) and increased with SPL. EEG arousals and awakenings were only associated with noise above 39 dBA in N2 sleep. K-complexes were 2 times more likely to occur in response to noise than EEG arousals or awakenings. Subjective noise sensitivity and hearing acuity were associated with K-complex occurrence, but not arousal or awakening. Noise type did not detectably influence K-complexes, EEG arousals or awakening responses.

CONCLUSION

These findings support that K-complexes are a sensitive marker of sensory processing of environmental noise during sleep and that increased hearing acuity and decreased self-reported noise sensitivity increase K-complex probability.

Decreased neuronal synaptosome associated protein 29 contributes to poststroke cognitive impairment by disrupting presynaptic maintenance

Background: Poststroke cognitive impairments are common in stroke survivors, and pose a high risk of incident dementia. However, the cause of these cognitive impairments is obscure and required an investigation.

Methods: Oxygen-glucose deprivation (OGD) model and middle cerebral artery occlusion (MCAO) model were used to imitate in vitro or in vivo acute cerebral ischemia, respectively. The differentially expressed synaptosome associated protein 29 (SNAP29)-interacting proteins upon ischemia and reperfusion were analyzed with bioinformatics analysis and the results indicated that the changes of SNAP29 after acute ischemia were mainly involved in the synaptic functions. The outcomes of SNAP29 reduction were assessed with SNAP29 knockdown, which mimicked the distribution of SNAP29 along neuronal processes after acute ischemia. Using the whole-cell patch clamp recording method and transmission electron microscope, the pre-synaptic function and readily releasable pool (RRP) were observed after SNAP29 knock down. Using photogenetic manipulations and behavioral tests, the neuronal projection and cognitive functions of mice with SNAP29 knock down in hippocampus CA1 region were evaluated.

Results: It was found that SNAP29 protein levels decreased in both in vitro and in vivo ischemic models. Further, the SNAP29 reduction wasn't associated with impaired autophagy flux and neuronal survival. When SNAP29 was knocked down in primary cortical neurons, the frequency of AMPARs-mediated mEPSCs, but not the amplitude, significantly decreased. Meanwhile, the mice with SNAP29 knockdown at CA1 region of hippocampus developed an impairment in hippocampus-mPFC (middle prefrontal cortex) circuit and behavioral dysfunctions. Moreover, the size of RRP at presynaptic sites was diminished.

Conclusion: Since SNAP29 protein levels didn't significantly influence the neuronal survival and its decrease was sufficient to disturb the neural circuit via a presynaptic manner, the SNAP29-associated strategies may be an efficient target against poststroke synaptic dysfunction and cognitive deficits.

Obstructive Sleep Apnea and Its Treatment in Aging: Effects on Alzheimer's disease Biomarkers, Cognition, Brain Structure and Neurophysiology

Here we review the impact of obstructive sleep apnea (OSA) on biomarkers of Alzheimer's disease (AD) pathogenesis, neuroanatomy, cognition and neurophysiology, and present the research investigating the effects of continuous positive airway pressure (CPAP) therapy. OSA is associated with an increase in AD markers amyloid-β and tau measured in cerebrospinal fluid (CSF), by Positron Emission Tomography (PET) and in blood serum. There is some evidence suggesting CPAP therapy normalizes AD biomarkers in CSF but since mechanisms for amyloid-β and tau production/clearance in humans are not completely understood, these findings remain preliminary. Deficits in the cognitive domains of attention, vigilance, memory and executive functioning are observed in OSA patients with the magnitude of impairment appearing stronger in younger people from clinical settings than in older community samples. Cognition improves with varying degrees after CPAP use, with the greatest effect seen for attention in middle age adults with more severe OSA and sleepiness. Paradigms in which encoding and retrieval of information are separated by periods of sleep with or without OSA have been done only rarely, but perhaps offer a better chance to understand cognitive effects of OSA than isolated daytime testing. In cognitively normal individuals, changes in EEG microstructure during sleep, particularly slow oscillations and spindles, are associated with biomarkers of AD, and measures of cognition and memory. Similar changes in EEG activity are reported in AD and OSA, such as "EEG slowing" during wake and REM sleep, and a degradation of NREM EEG microstructure. There is evidence that CPAP therapy partially reverses these changes but large longitudinal studies demonstrating this are lacking. A diagnostic definition of OSA relying solely on the Apnea Hypopnea Index (AHI) does not assist in understanding the high degree of inter-individual variation in daytime impairments related to OSA or response to CPAP therapy. We conclude by discussing conceptual challenges to a clinical trial of OSA treatment for AD prevention, including inclusion criteria for age, OSA severity, and associated symptoms, the need for a potentially long trial, defining relevant primary outcomes, and which treatments to target to optimize treatment adherence.

Beyond K-complex binary scoring during sleep: probabilistic classification using deep learning

STUDY OBJECTIVES

K-complexes (KCs) are a recognized electroencephalography marker of sensory processing and a defining feature of sleep stage 2. KC frequency and morphology may also be reflective of sleep quality, aging, and a range of sleep and sensory processing deficits. However, manual scoring of K-complexes is impractical, time-consuming, and thus costly and currently not well-standardized. Although automated KC detection methods have been developed, performance and uptake remain limited.

METHODS

The proposed algorithm is based on a deep neural network and Gaussian process, which gives the input waveform a probability of being a KC ranging from 0% to 100%. The algorithm was trained on half a million synthetic KCs derived from manually scored sleep stage 2 KCs from the Montreal Archive of Sleep Study containing 19 healthy young participants. Algorithm performance was subsequently assessed on 700 independent recordings from the Cleveland Family Study using sleep stages 2 and 3 data.

RESULTS

The developed algorithm showed an F1 score (a measure of binary classification accuracy) of 0.78 and thus outperforms currently available KC scoring algorithms with F1 = 0.2-0.6. The probabilistic approach also captured expected variability in KC shape and amplitude within individuals and across age groups.

CONCLUSIONS

An automated probabilistic KC classification is well suited and effective for systematic KC detection for a more in-depth exploration of potential relationships between KCs during sleep and clinical outcomes such as health impacts and daytime symptomatology.

Cortical source localization of sleep-stage specific oscillatory activity

The oscillatory features of non-REM sleep states have been a subject of intense research over many decades. However, a systematic spatial characterization of the spectral features of cortical activity in each sleep state is not available yet. Here, we used magnetoencephalography (MEG) and electroencephalography (EEG) recordings during night sleep. We performed source reconstruction based on the individual subject’s anatomical magnetic resonance imaging (MRI) scans and spectral analysis on each non-REM sleep epoch in eight standard frequency bands, spanning the complete spectrum, and computed cortical source reconstructions of the spectral contrasts between each sleep state in comparison to the resting wakefulness. Despite not distinguishing periods of high and low activity within each sleep stage, our results provide new information about relative overall spectral changes in the non-REM sleep stages.

The human K-complex: Insights from combined scalp-intracranial EEG recordings

Sleep spindles and K-complexes (KCs) are a hallmark of N2 sleep. While the functional significance of spindles is comparatively well investigated, there is still ongoing debate about the role of the KC: it is unclear whether it is a cortical response to an arousing stimulus (either external or internal) or whether it has sleep-promoting properties. Invasive intracranial EEG recordings from individuals with drug-resistant epilepsy offer a unique opportunity to study in-situ human brain physiology. To better understand the function of the KC, we aimed to (i) investigate the intracranial correlates of spontaneous scalp KCs, and (ii) compare the intracranial activity of scalp KCs associated or not with arousals. Whole-night recordings from adults with drug-resistant focal epilepsy who underwent combined intracranial-scalp EEG for pre-surgical evaluation at the Montreal Neurological Institute between 2010 and 2018 were selected. KCs were visually marked in the scalp and categorized according to the presence of microarousals: (i) Pre-microarousal KCs; (ii) KCs during an ongoing microarousal; and (iii) KCs without microarousal. Power in different spectral bands was computed to compare physiological intracranial EEG activity at the time of scalp KCs relative to the background, as well as to compare microarousal subcategories. A total of 1198 scalp KCs selected from 40 subjects were analyzed, resulting in 32,504 intracranial KC segments across 992 channels. Forty-seven percent of KCs were without microarousal, 30% were pre-microarousal, and 23% occurred during microarousals. All scalp KCs were accompanied by widespread cortical increases in delta band power (0.3-4 ​Hz) relative to the background: the highest percentages were observed in the parietal (60-65%) and frontal cortices (52-58%). Compared to KCs without microarousal, pre-microarousal KCs were accompanied by increases (66%) in beta band power (16-30 ​Hz) in the motor cortex, which was present before the peak of the KC. In addition, spatial distribution of spectral power changes following each KC without microarousal revealed that certain brain regions were associated with increases in delta power (25-62%) or decreases in alpha/beta power (11-24%), suggesting a sleep-promoting pattern, whereas others were accompanied by increases of higher frequencies (12-27%), suggesting an arousal-related pattern. This study shows that KCs can be generated across widespread cortical areas. Interestingly, the motor cortex shows awake-like EEG activity before the onset of KCs followed by microarousals. Our findings also highlight region-specific sleep- or arousal-promoting responses following KCs, suggesting a dual role for the human KC.

Hyperarousal captured in increased number of arousal events during pre-REM periods in individuals with frequent nightmares

The aim of this study was to investigate hyperarousal in individuals with frequent nightmares (NM participants) by calculating arousal events during nocturnal sleep. We hypothesized an increased number of arousals in NM participants compared with controls, especially during those periods where the probability of spontaneous arousal occurrence is already high, such as non-rapid eye movement to rapid eye movement transitions (pre-rapid eye movement periods). Twenty-two NM participants and 23 control participants spent two consecutive nights in our sleep laboratory, monitored by polysomnography. Arousal number and arousal length were calculated only for the second night, for 10 min before rapid eye movement (pre-rapid eye movement) and 10 min after rapid eye movement (post-rapid eye movement) periods, as well as non-rapid eye movement and rapid eye movement phases separately. Repeated-measures ANOVA model testing revealed significant Group (NM participants, controls) × Phase (pre-rapid eye movement, post-rapid eye movement) interaction in case of the number of arousals. Furthermore, post hoc analysis showed a significantly increased number of arousals during pre-rapid eye movement periods in NM participants, compared with controls, a difference that disappeared in post-rapid eye movement periods. We propose that focusing the analyses of arousals specifically on state transitory periods offers a unique perspective into the fragile balance between the sleep-promoting and arousal systems. This outlook revealed an increased number of arousals in NM participants, reflecting hyperarousal during pre-rapid eye movement periods.

Cortical hyperarousal in NREM sleep normalizes from pre- to post- REM periods in individuals with frequent nightmares

Study Objectives

Frequent nightmares have a high prevalence and constitute a risk factor for psychiatric conditions, but their pathophysiology is poorly understood. Our aim was to examine sleep architecture and electroencephalographic markers—with a specific focus on state transitions—related to sleep regulation and hyperarousal in participants with frequent nightmares (NM participants) versus healthy controls.

Methods

Healthy controls and NM participants spent two consecutive nights in the sleep laboratory. Second night spectral power during NREM to REM sleep (pre-REM) and REM to NREM (post-REM) transitions as well as during NREM and REM periods were evaluated for 22 NM participants compared to 22 healthy controls with a similar distribution of age, gender, and dream recall frequency.

Results

We found significant differences between the groups in the pre-REM to post-REM changes in low- and high-frequency domains. NM participants experienced a lower amount of slow-wave sleep and showed increased beta and gamma power during NREM and pre-REM periods. No difference was present during REM and post-REM phases. Furthermore, while increased pre-REM high-frequency power seems to be mainly driven by post-traumatic stress disorder (PTSD) symptom intensity, decreased low-frequency activity occurred regardless of PTSD symptom severity.

Conclusion

Our findings indicate that NM participants had increased high-frequency spectral power during NREM and pre-REM periods, as well as relatively reduced slow frequency and increased fast frequency spectral power across pre-and post-REM periods. This combination of reduced sleep-protective activity and increased hyperarousal suggests an imbalance between sleep regulatory and wake-promoting systems in NM participants.

Isolated rapid eye movement sleep behavior disorder and cyclic alternating pattern: is sleep microstructure a predictive parameter of neurodegeneration?

Objective

To evaluate the role of sleep cyclic alternating pattern (CAP) in patients with isolated REM sleep behavior disorder (IRBD) and ascertain whether CAP metrics might represent a marker of phenoconversion to a defined neurodegenerative condition.

Methods

Sixty-seven IRBD patients were included and classified into patients who phenoconverted to a neurodegenerative disease (RBD converters: converter REM sleep behavior disorder [cRBD]; n = 34) and remained disease-free (RBD non-converters: non-converter REM sleep behavior disorder [ncRBD]; n = 33) having a similar follow-up duration. Fourteen age- and gender-balanced healthy controls were included for comparisons.

Results

Compared to controls, CAP rate and CAP index were significantly decreased in IRBD mainly due to a decrease of A1 phase subtypes (A1 index) despite an increase in duration of both CAP A and B phases. The cRBD group had significantly lower values of CAP rate and CAP index when compared with the ncRBD group and controls. A1 index was significantly reduced in both ncRBD and cRBD groups compared to controls. When compared to the ncRBD group, A3 index was significantly decreased in the cRBD group. The Kaplan-Meier curve applied to cRBD estimated that a value of CAP rate below 32.9% was related to an average risk of conversion of 9.2 years after baseline polysomnography.

Conclusion

IRBD is not exclusively a rapid eye movement (REM) sleep parasomnia, as non-rapid eye movement (non-REM) sleep microstructure can also be affected by CAP changes. Further studies are necessary to confirm that a reduction of specific CAP metrics is a marker of neurodegeneration in IRBD.

The heritability of the human K-complex: a twin study

Sleep electroencephalogram (EEG) has a trait-like nature. Several findings highlighted the heritability of spectral power in specific frequency ranges and sleep spindles during nonrapid eye movement (NREM) sleep. However, a genetic influence on the K-complex (KC), one of the electrophysiological hallmarks of NREM sleep, has never been assessed. Here, we investigated the heritability of the KC detected during NREM stage 2 comparing 10 monozygotic (MZ) and 10 dizygotic (DZ) twin pairs. Genetic variance analysis (GVA) and intraclass correlation coefficients (ICCs) were performed to assess the genetic effect and within-pair similarity for KC density, amplitude, and for the area under the curve (AUC) of the KC average waveform at Fz, Cz, and Pz scalp locations. Moreover, cluster analysis was performed on the KC average waveform profile. We observed a significant genetic effect on KC AUC at Cz and Pz, and on amplitude at Pz. Within-pair similarity (ICCs) was always significant for MZ twins except for KC density at Fz, whereas DZ twins always exhibited ICCs below the significance threshold, with the exception of density at Pz. The largest differences in within-pair similarity between MZ and DZ groups were observed again for AUC at Cz and Pz. MZ pairs accurately clustered for the KC average waveform with a higher frequency (successful clustering rate for MZ pairs: Fz = 60%; Cz = 80%; Pz = 90%) compared with DZ pairs (successful clustering rate for DZ pairs: Fz = 10%; Cz = 10%; Pz = none). Our results suggest the existence of a genetic influence on the human KC, particularly related to its morphology and maximally observable in central and parietal locations.

Regulation of Local Sleep by the Thalamic Reticular Nucleus

In spite of the uniform appearance of sleep as a behavior, the sleeping brain does not produce electrical activities in unison. Different types of brain rhythms arise during sleep and vary between layers, areas, or from one functional system to another. Local heterogeneity of such activities, here referred to as local sleep, overturns fundamental tenets of sleep as a globally regulated state. However, little is still known about the neuronal circuits involved and how they can generate their own specifically-tuned sleep patterns. NREM sleep patterns emerge in the brain from interplay of activity between thalamic and cortical networks. Within this fundamental circuitry, it now turns out that the thalamic reticular nucleus (TRN) acts as a key player in local sleep control. This is based on a marked heterogeneity of the TRN in terms of its cellular and synaptic architecture, which leads to a regional diversity of NREM sleep hallmarks, such as sleep spindles, delta waves and slow oscillations. This provides first evidence for a subcortical circuit as a determinant of cortical local sleep features. Here, we review novel cellular and functional insights supporting TRN heterogeneity and how these elements come together to account for local NREM sleep. We also discuss open questions arising from these studies, focusing on mechanisms of sleep regulation and the role of local sleep in brain plasticity and cognitive functions.

Increased cortical involvement and synchronization during CAP A1 slow waves

Slow waves recorded with EEG in NREM sleep are indicative of the strength and spatial extent of synchronized firing in neuronal assemblies of the cerebral cortex. Slow waves often appear in the A1 part of the cyclic alternating patterns (CAP), which correlate with a number of behavioral and biological parameters, but their physiological significance is not adequately known. We automatically detected slow waves from the scalp recordings of 37 healthy patients, visually identified CAP A1 events and compared slow waves during CAP A1 with those during NCAP. For each slow wave, we computed the amplitude, slopes, frequency, synchronization (synchronization likelihood) between specific cortical areas, as well as the location of origin and scalp propagation of individual waves. CAP A1 slow waves were characterized by greater spatial extent and amplitude, steeper slopes and greater cortical synchronization, but a similar prominence in frontal areas and similar propagation patterns to other areas on the scalp. Our results indicate that CAP A1 represents a period of highly synchronous neuronal firing over large areas of the cortical mantle. This feature may contribute to the role CAP A1 plays in both normal synaptic homeostasis and in the generation of epileptiform phenomena in epileptic patients.

Sleepless Night and Day, the Plight of Progressive Supranuclear Palsy

Objectives

To elucidate the unique sleep and waking characteristics in progressive supranuclear palsy (PSP), a neurodegenerative disease associated with motor deficits and dementia that largely affects the brainstem and thalamic regions.

Methods

A total of 20 PSP and 16 healthy older adult controls participated in this study. The participants underwent an overnight polysomnography and multiple sleep latency test (MSLT) the following day. Prior to the MSLT last trial, they were asked to complete the Stanford Sleepiness Scale. Data were assessed for measures of latency to sleep onset, sleep duration, waking, and sleep staging during the night. Mean sleep latency, a measure of daytime sleepiness, sleep onset rapid eye movement (REM) periods, and microsleeps were studied with the MSLT. Spectral analysis of wake electroencephalogram (EEG) was performed for 30-second periods at the start of each MSLT trial.

Results

PSP took significantly longer time to fall asleep (p < .001), slept less during the night (p ≤ .001), and had more wake after sleep onset than controls (p ≤ .001). PSP had less N2 sleep (p < .05) and N3 sleep (p < .05), and REM sleep (p < .001) than controls. During the MSLT, PSP took significantly longer to fall asleep (p < .001), did not have microsleeps when they remained awake throughout the assessment periods, but were subjectively sleepier than controls (p < .05). Gamma power was increased during wake EEG in PSP (p < .01).

Conclusions

Sleep/waking regulation and REM sleep regulation are disrupted in PSP, leading to profound sleep deprivation without recuperation. Our findings suggest a diminished homeostatic sleep drive in PSP. This hyperaroused state is unique and is a severely disabling feature of PSP.

Observed Relationship Behaviors and Sleep in Military Veterans and Their Partners

BACKGROUND

Emerging research has begun to examine associations between relationship functioning and sleep. However, these studies have largely relied on self-reported evaluations of relationships and/or of sleep, which may be vulnerable to bias.

PURPOSE

The purpose of the study was to examine associations between relationship functioning and sleep in military couples. This is the first research to examine associations between observed relationship behaviors and subjective and polysomnographically measured sleep in a sample at-risk for both sleep and relationship problems.

METHODS

The sample included 35 military veterans and their spouses/partners. Marital functioning was coded from a videotaped conflict interaction. Analyses focused on behavioral codes of hostility and relationship-enhancing attributions. Sleep was assessed via self-report and in-home polysomnography.

RESULTS

Greater hostility was associated with poorer sleep efficiency for oneself (b = -0.195, p = .013). In contrast, greater relationship-enhancing attributions were associated with higher percentages of stage N3 sleep (b = 0.239, p = .028). Partners' hostility was also positively associated with higher percentages of stage N3 sleep (b = 0.272, p = .010). Neither hostility nor relationship-enhancing attributions was associated with self-reported sleep quality, percentage of REM sleep, or total sleep time.

CONCLUSIONS

Both partners' positive and negative behaviors during conflict interactions were related to sleep quality. These findings highlight the role that effective communication and conflict resolution skills may play in shaping not only the marital health of veterans and their spouses but also the physical health of both partners as well. Understanding the links between relationship functioning and sleep may be important targets of intervention in the aftermath of war.

Neural Markers of Responsiveness to the Environment in Human Sleep

Sleep is characterized by a loss of behavioral responsiveness. However, recent research has shown that the sleeping brain is not completely disconnected from its environment. How neural activity constrains the ability to process sensory information while asleep is yet unclear. Here, we instructed human volunteers to classify words with lateralized hand responses while falling asleep. Using an electroencephalographic (EEG) marker of motor preparation, we show how responsiveness is modulated across sleep. These modulations are tracked using classic event-related potential analyses complemented by Lempel-Ziv complexity (LZc), a measure shown to track arousal in sleep and anesthesia. Neural activity related to the semantic content of stimuli was conserved in light non-rapid eye movement (NREM) sleep. However, these processes were suppressed in deep NREM sleep and, importantly, also in REM sleep, despite the recovery of wake-like neural activity in the latter. In NREM sleep, sensory activations were counterbalanced by evoked down states, which, when present, blocked further processing of external information. In addition, responsiveness markers correlated positively with baseline complexity, which could be related to modulation in sleep depth. In REM sleep, however, this relationship was reversed. We therefore propose that, in REM sleep, endogenously generated processes compete with the processing of external input. Sleep can thus be seen as a self-regulated process in which external information can be processed in lighter stages but suppressed in deeper stages. Last, our results suggest drastically different gating mechanisms in NREM and REM sleep.

SIGNIFICANCE STATEMENT

Previous research has tempered the notion that sleepers are isolated from their environment. Here, we pushed this idea forward and examined, across all sleep stages, the brain's ability to flexibly process sensory information, up to the decision level. We extracted an EEG marker of motor preparation to determine the completion of the sensory processing chain and explored how it is constrained by baseline and evoked neural activity. In NREM sleep, slow waves elicited by stimuli appeared to block response preparation. We also used a novel analytic approach (Lempel-Ziv complexity) and showed that the ability to process external information correlates with neural complexity. A reversal of the correlation between complexity and motor indices in REM sleep suggests drastically different gating mechanisms across sleep stages.

Altered sleep homeostasis correlates with cognitive impairment in patients with focal epilepsy

In animal studies, both seizures and interictal spikes induce synaptic potentiation. Recent evidence suggests that electroencephalogram slow wave activity during sleep reflects synaptic potentiation during wake, and that its homeostatic decrease during the night is associated with synaptic renormalization and its beneficial effects. Here we asked whether epileptic activity induces plastic changes that can be revealed by high-density electroencephalography recordings during sleep in 15 patients with focal epilepsy and 15 control subjects. Compared to controls, patients with epilepsy displayed increased slow wave activity power during non-rapid eye movement sleep over widespread, bilateral scalp regions. This global increase in slow wave activity power was positively correlated with the frequency of secondarily generalized seizures in the 3-5 days preceding the recordings. Individual patients also showed local increases in sleep slow wave activity power at scalp locations matching their seizure focus. This local increase in slow wave activity power was positively correlated with the frequency of interictal spikes during the last hour of wakefulness preceding sleep. By contrast, frequent interictal spikes during non-rapid eye movement sleep predicted a reduced homeostatic decrease in the slope of sleep slow waves during the night, which in turn predicted reduced daytime learning. Patients also showed an increase in sleep spindle power, which was negatively correlated with intelligence quotient. Altogether, these findings suggest that both seizures and interictal spikes may induce long-lasting changes in the human brain that can be sensitively detected by electroencephalographic markers of sleep homeostasis. Furthermore, abnormalities in sleep markers are correlated with cognitive impairment, suggesting that not only seizures, but also interictal spikes can have negative consequences.

Depressive Symptoms Are Associated With Objectively Measured Sleep Parameters in Kidney Transplant Recipients

STUDY OBJECTIVES

Both depression and sleep complaints are very prevalent among kidney transplant (kTx) recipients. However, details of the complex relationship between sleep and depression in this population are not well documented. Thus, we investigated the association between depressive symptoms and sleep macrostructure parameters among prevalent kTx recipients.

METHODS

Ninety-five kTx recipients participated in the study (54 males, mean ± standard devation age 51 ± 13 years, body mass index 26 ± 4 kg/m2, estimated glomerular filtration rate 53 ± 19 ml/min/1.73 m2). Symptoms of depression were assessed by the Center for Epidemiologic Studies - Depression Scale (CES-D). After 1-night polysomnography each recording was visually scored and sleep macrostructure was analyzed.

RESULTS

The CES-D score was significantly associated with the amount of stage 2 sleep (r = 0.20, P < .05), rapid eye movement (REM) latency (r = 0.21, P < .05) and REM percentage (r = -0.24, P < .05), but not with the amount of slow wave sleep (r = -0.12, P > .05). In multivariable linear regression models the CES-D score was independently associated with the amount of stage 2 sleep (β: 0.205; confidence interval: 0.001-0.409; P = .05) and REM latency (β: 0.234; confidence interval: 0.001-0.468; P = .05) after adjustment for potential confounders.

CONCLUSIONS

Depressive symptoms among kTx recipients are associated with increased amount of stage 2 sleep and prolonged REM latency. Further studies are needed to confirm our findings and understand potential clinical implications.

Influence of Fragrances on Human Psychophysiological Activity: With Special Reference to Human Electroencephalographic Response

The influence of fragrances such as perfumes and room fresheners on the psychophysiological activities of humans has been known for a long time, and its significance is gradually increasing in the medicinal and cosmetic industries. A fragrance consists of volatile chemicals with a molecular weight of less than 300 Da that humans perceive through the olfactory system. In humans, about 300 active olfactory receptor genes are devoted to detecting thousands of different fragrance molecules through a large family of olfactory receptors of a diverse protein sequence. The sense of smell plays an important role in the physiological effects of mood, stress, and working capacity. Electrophysiological studies have revealed that various fragrances affected spontaneous brain activities and cognitive functions, which are measured by an electroencephalograph (EEG). The EEG is a good temporal measure of responses in the central nervous system and it provides information about the physiological state of the brain both in health and disease. The EEG power spectrum is classified into different frequency bands such as delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz) and gamma (30-50 Hz), and each band is correlated with different features of brain states. A quantitative EEG uses computer software to provide the topographic mapping of the brain activity in frontal, temporal, parietal and occipital brain regions. It is well known that decreases of alpha and beta activities and increases of delta and theta activities are associated with brain pathology and general cognitive decline. In the last few decades, many scientific studies were conducted to investigate the effect of inhalation of aroma on human brain functions. The studies have suggested a significant role for olfactory stimulation in the alteration of cognition, mood, and social behavior. This review aims to evaluate the available literature regarding the influence of fragrances on the psychophysiological activities of humans with special reference to EEG changes.