Spectral characteristics of sleep EEG in chronic insomnia

Acute and Chronic Insomnia: What Has Time and/or Hyperarousal Got to Do with It?

Nearly one-third of the population reports new onset or acute insomnia in a given year. Similarly, it is estimated that approximately 10% of the population endorses sleep initiation and maintenance problems consistent with diagnostic criteria for chronic insomnia. For decades, acute and chronic insomnia have been considered variations of the same condition or disorder, only really differentiated in terms of chronicity of symptoms (days/weeks versus months). Whether or not acute and chronic insomnia are part of the same phenomena is an important question, one that has yet to be empirically evaluated. The goal of the present theoretical review was to summarize the definitions of acute and chronic insomnia and discuss the role that hyperarousal may have in explaining how the pathophysiology of acute and chronic insomnia is likely different (i.e., what biopsychological factors precipitate and/or perpetuate acute insomnia, chronic insomnia, or both?).

Correlation-based ECG Artifact Correction from Single Channel EEG using Modified Variational Mode Decomposition

BACKGROUND AND OBJECTIVE

Ambulatory based healthcare system use limited electrodes for electroencephalogram (EEG) acquisition at concerned electrode position, to minimize the instrumentation and computational complexity. But, again the possibility of contamination is inevitable depending on the electrode position on the scalp. This paper proposes an electrocardiogram (ECG) artifact correction algorithm in the absence of coherent ECG for automatic analysis/diagnosis of the acquired contaminated single channel EEG signal.

METHODS

The proposed algorithm uses an enhanced and modified version of signal decomposition i.e. modified variational mode decomposition (mVMD) to obtain band limited intrinsic mode functions (BLIMFs) from EEG epoch. The mVMD is found to be useful when the signal contains properties that are correlated. Further, exploiting the correlation among the obtained mode functions the ECG artifact components are identified. An ECG reference is estimated and QRS complexes are suppressed. The effective EEG reconstruction is performed by simply adding the remaining BLIMFs to QRS complex suppressed estimated reference. This is owing to the robust reconstruction feature provided by mVMD.

RESULTS

Upon the comparative evaluation for both real and semi-simulated dataset, the proposed algorithm is providing less distortion to the EEG brain activity frequency bands, and is also less computationally intensive than the existing Ensembled empirical mode decomposition (EEMD) based algorithm that requires ECG reference channel. Evaluation of semi-simulated dataset obtained an average correlation of 97% between EEG signals before contamination and after correction of ECG artifact.

CONCLUSION

The proposed algorithm efficiently corrects the ECG artifact from EEG while overcoming the limitations such as, (1) requirement of a reference ECG channel, (2) requirement of R-R interval or amplitude thresholding for QRS complex identification.

On the Hierarchical Organization of Oscillatory Assemblies: Layered Superimposition and a Global Bioelectric Framework

Bioelectric oscillations occur throughout the nervous system of nearly all animals, revealed to play an important role in various aspects of cognitive activity such as information processing and feature binding. Modern research into this dynamic and intrinsic bioelectric activity of neural cells continues to raise questions regarding their role in consciousness and cognition. In this theoretical article, we assert a novel interpretation of the hierarchical nature of "brain waves" by identifying that the superposition of multiple oscillations varying in frequency corresponds to the superimposing of the contents of consciousness and cognition. In order to describe this isomorphism, we present a layered model of the global functional oscillations of various frequencies which act as a part of a unified metastable continuum described by the Operational Architectonics theory and suggested to be responsible for the emergence of the phenomenal mind. We detail the purposes, functions, and origins of each layer while proposing our main theory that the superimposition of these oscillatory layers mirrors the superimposition of the components of the integrated phenomenal experience as well as of cognition. In contrast to the traditional view that localizations of high and low-frequency activity are spatially distinct, many authors have suggested a hierarchical nature to oscillations. Our theoretical interpretation is founded in four layers which correlate not only in frequency but in evolutionary development. As other authors have done, we explore how these layers correlate to the phenomenology of human experience. Special importance is placed on the most basal layer of slow oscillations in coordinating and grouping all of the other layers. By detailing the isomorphism between the phenomenal and physiologic aspects of how lower frequency layers provide a foundation for higher frequency layers to be organized upon, we provide a further means to elucidate physiological and cognitive mechanisms of mind and for the well-researched outcomes of certain voluntary breathing patterns and meditative practices which modulate the mind and have therapeutic effects for psychiatric and other disorders.

Data-Driven Analysis of EEG Reveals Concomitant Superficial Sleep During Deep Sleep in Insomnia Disorder

Study Objectives: The subjective suffering of people with Insomnia Disorder (ID) is insufficiently accounted for by traditional sleep classification, which presumes a strict sequential occurrence of global brain states. Recent studies challenged this presumption by showing concurrent sleep- and wake-type neuronal activity. We hypothesized enhanced co-occurrence of diverging EEG vigilance signatures during sleep in ID.

Methods: Electroencephalography (EEG) in 55 cases with ID and 64 controls without sleep complaints was subjected to a Latent Dirichlet Allocation topic model describing each 30 s epoch as a mixture of six vigilance states called Topics (T), ranked from N3-related T1 and T2 to wakefulness-related T6. For each stable epoch we determined topic dominance (the probability of the most likely topic), topic co-occurrence (the probability of the remaining topics), and epoch-to-epoch transition probabilities.

Results: In stable epochs where the N1-related T4 was dominant, T4 was more dominant in ID than in controls, and patients showed an almost doubled co-occurrence of T4 during epochs where the N3-related T1 was dominant. Furthermore, patients had a higher probability of switching from T1- to T4-dominated epochs, at the cost of switching to N3-related T2-dominated epochs, and a higher probability of switching from N2-related T3- to wakefulness-related T6-dominated epochs.

Conclusion: Even during their deepest sleep, the EEG of people with ID express more N1-related vigilance signatures than good sleepers do. People with ID are moreover more likely to switch from deep to light sleep and from N2 sleep to wakefulness. The findings suggest that hyperarousal never rests in ID.

Childhood high-frequency EEG activity during sleep is associated with incident insomnia symptoms in adolescence

BACKGROUND

Insomnia has been associated in cross-sectional studies with increased beta (15-35 Hz) electroencephalogram (EEG) power during nonrapid eye movement (NREM) sleep, an index of cortical hyperarousal. However, it is unknown whether this cortical hyperarousal is present before individuals with insomnia develop the disorder. To fill this gap, we examined the association of childhood sleep high-frequency EEG activity with incident insomnia symptoms (i.e., absence of insomnia symptoms in childhood but presence in adolescence).

METHODS

We studied a case-control subsample of 45 children (6-11 years) from the Penn State Child Cohort, a population-based random sample of 421 children, who were followed up after 8 years as adolescents (13-20 years). We examined low-beta (15-25 Hz) and high-beta (25-35 Hz) relative power at central EEG derivations during NREM sleep and, in secondary analyses, during sleep onset latency, sleep onset, and REM sleep. Incident insomnia symptoms were defined as the absence of parent-reported difficulty falling and/or staying asleep during childhood and a self-report of these insomnia symptoms during adolescence.

RESULTS

Childhood high-beta power during NREM sleep was significantly increased in children who developed insomnia symptoms in adolescence (n = 25) as compared to normal sleeping controls (n = 20; p = .03). Multivariable-adjusted logistic regression models showed that increased childhood high-beta EEG power during NREM sleep was associated with a threefold increased odds (95% CI = 1.12-7.98) of incident insomnia symptoms in adolescence. No other significant relationships were observed for other sleep/wake states or EEG frequency bands.

CONCLUSIONS

Increased childhood high-frequency EEG power during NREM sleep is associated with incident insomnia symptoms in adolescence. This study indicates that cortical hyperarousal during sleep may be a premorbid neurophysiological sign of insomnia, which may mediate the increased risk of psychiatric disorders associated with insomnia.

Implication of Fast Activities of Spectral Analysis in Subjective Sleep Complaints of Elderly Women

OBJECTIVE

In elderly patients, women have better qualities of sleep than men in objective parameters; however, women subjectively complain more about sleep disturbances than men. We performed visual scoring and spectral analysis of sleep electroencephalograms to explain these gender differences in the degree of arousal, the most representative marker in insomnia.

METHODS

A total of 354 participants (≥60 years old) were recruited from a Korean community underwent nocturnal polysomnography (NPSG). A Fast Fourier transform was used for the spectral analysis of the NPSG data. Relative power was calculated as absolute power of each band divided by total absolute power. Difference in total sleep time (D_TST) is obtained by subtracting the total sleep time reported in Pittsburgh Sleep Quality Index (PSQI) from the TST measured by the NPSG.

RESULTS

A total of 75 participants (women, 51) were finally analyzed. Women had higher PSQI, longer sleep latencies, sleep inefficiencies, and daytime dysfunctions compared to men. The percentage of stage 1 sleep was higher in men versus in women, whereas percentage of stage 3 sleep was higher in women than in men ( P = .001; P = .001). Women had higher relative alpha and beta powers than men during nonrapid eye movement (NREM) sleep ( P = .017; P = .015). During NREM sleep, beta power was negatively correlated with D_TST ( R = -0.250, P = .033), and relative alpha power in stage 3 sleep was positively correlated with sleep latency in PSQI ( R = 0.267, P = .022).

CONCLUSION

Spectral analysis showed that women had more disturbed sleep than men. The result from the spectral analysis may explain hyperarousal in elderly women.

Altered ultradian cortisol rhythmicity as a potential neurobiologic substrate for chronic insomnia

Chronic insomnia is highly prevalent and associated with significant morbidity (i.e., confers risk for multiple psychiatric and medical disorders, such as depression and hypertension). Therefore, it is essential to identify factors that perpetuate this disorder. One candidate factor in the neurobiology of chronic insomnia is hypothalamic-pituitary-adrenal-axis dysregulation, and in particular, alterations in circadian cortisol rhythmicity. Cortisol secretory patterns, however, fluctuate with both a circadian and an ultradian rhythm (i.e., pulses every 60-120 min). Ultradian cortisol pulses are thought to be involved in the maintenance of wakefulness during the day and their relative absence at night may allow for the consolidation of sleep and/or shorter nocturnal awakenings. It is possible that the wakefulness that occurs in chronic insomnia may be associated with the aberrant occurrence of cortisol pulses at night. While cortisol pulses naturally occur with transient awakenings, it may also be the case that cortisol pulsatility becomes a conditioned phenomenon that predisposes one to awaken and/or experience prolonged nocturnal awakenings. The current review summarizes the literature on cortisol rhythmicity in subjects with chronic insomnia, and proffers the suggestion that it may be abnormalities in the ultradian rather than circadian cortisol that is associated with the pathophysiology of insomnia.

State-Dependent Modulation of Visual Evoked Potentials in a Rodent Genetic Model of Electroencephalographic Instability

Despite normal sleep timing and duration, Egr3-deficient (Egr3^−/−) mice exhibit electroencephalographic (EEG) characteristics of reduced arousal, including elevated slow wave (1–4 Hz) activity during wakefulness. Here we show that these mice exhibit state-dependent instability in the EEG. Intermittent surges in EEG power were found in Egr3^−/− mice during wakefulness and rapid eye movement sleep, most prominently in the beta (15–35 Hz) range compared to wild type (Egr3^+/+) mice. Such surges did not coincide with sleep onset, as the surges were not associated with cessation of electromyographic tone. Cortical processing of sensory information by visual evoked responses (VEP) were found to vary as a function of vigilance state, being of higher magnitude during slow wave sleep (SWS) than wakefulness and rapid eye movement sleep. VEP responses were significantly larger during quiet wakefulness than active wakefulness, in both Egr3^−/− mice and Egr3^+/+ mice. EEG synchronization in the beta range, previously linked to the accumulation of sleep need over time, predicted VEP magnitude. Egr3^−/− mice not only displayed elevated beta activity, but in quiet wake, this elevated beta activity coincides with an elevated evoked response similar to that of animals in SWS. These data confirm that (a) VEPs vary as a function of vigilance state, and (b) beta activity in the EEG is a predictor of state-dependent modulation of visual information processing. The phenotype of Egr3^−/− mice indicates that Egr3 is a genetic regulator of these phenomena.

Altered Regional Cortical Brain Activity in Healthy Subjects After Sleep Deprivation: A Functional Magnetic Resonance Imaging Study

Objective: To investigate acute sleep deprivation (SD)-related regional brain activity changes and their relationships with behavioral performances.

Methods: Twenty-two female subjects underwent an MRI scan and an attention network test at rested wakefulness (RW) status and after 24 h SD. The amplitude of low-frequency fluctuations (ALFF) was used to investigate SD-related regional brain activity changes. We used the receiver operating characteristic (ROC) curve to evaluate the ability of the ALFF differences in regional brain areas to distinguish the SD status from the RW status. We used Pearson correlations to evaluate the relationships between the ALFF differences in brain areas and the behavioral performances during the SD status.

Results: Subjects at the SD status exhibited a lower accuracy rate and a longer reaction time relative to the RW status. Compared with RW, SD showed significant lower ALFF values in the right cerebellum anterior lobe, and higher ALFF areas in the bilateral inferior occipital gyrus, left thalamus, left insula, and bilateral postcentral gyrus. The area under the curve values of the specific ALFF differences in brain areas were (mean ± std, 0.851 ± 0.045; 0.805–0.93). Further, the ROC curve analysis demonstrated that the ALFF differences in those regional brain areas alone discriminated the SD status from the RW status with high degrees of sensitivities (82.16 ± 7.61%; 75–93.8%) and specificities (81.23 ± 11.39%; 62.5–93.7%). The accuracy rate showed negative correlations with the left inferior occipital gyrus, left thalamus, and left postcentral gyrus, and showed a positive correlation with the right cerebellum.

Conclusions: The ALFF analysis is a potential indicator for detecting the excitation–inhibition imbalance of regional cortical activations disturbed by acute SD with high performances.

Sleep EEG spectral power is correlated with subjective-objective discrepancy of sleep onset latency in major depressive disorder

We aimed to identify the sleep electroencephalography (EEG) spectral power correlates of the subjective-objective discrepancy (SOD) of sleep onset latency (SOL) in major depressive disorder (MDD), primary insomnia (PI), and normal sleeping control (NSC) groups. We examined relative power values in standard frequency bands of the EEG spectra during the first Non-Rapid Eye Movement (NREM) sleep period as correlates of SOD of SOL between sleep diary and polysomnography in MDD (n = 36), PI (n = 19), and NSC (n = 23) groups. We also compared the relative spectral power of sleep EEG among MDD (n = 40), PI (n = 19), and NSC (n = 23) groups. SOD of SOL in MDD patients was positively correlated with relative sigma (r = 0.622, p corrected < 0.001), beta power (r = 0.559, p corrected = 0.002), and alpha power (r = 0.469, p corrected = 0.024) in the first NREM sleep period. There was no significant difference of sleep EEG power spectra among the three groups. SOD was positively correlated with high frequency EEG in MDD. High frequency EEG power is thought to be associated with hyperarousal and memory consolidation, and future larger-scale studies may further elucidate the neurophysiological mechanisms underlying SOD of sleep onset duration.

Instant sedative effect of acupuncture at GV20 on the frequency of electroencephalogram α and β waves in a model of sleep deprivation

Sleep deprivation (SD) adversely affects brain function and is accompanied by frequency-dependent changes in electroencephalograms (EEGs). Recent studies have suggested that acupuncture is an emerging alternative therapy for SD. However, the involvement of the frequency of EEG α and β waves in the protective effect of acupuncture against SD remains unknown. The present study investigated the instant effect of acupuncture at GV20 on insomnia by analyzing the frequency of α and β waves using electroencephalography in a model of sleep deprivation. A total of 16 rats (Wistar; male; weight, 340±10 g) were divided randomly into four groups (4 rats per group) to create a rat model of sleep deprivation using the modified multiple platform method in the GV20 group, the sham acupoint group and the model group. After 72 h of sleep deprivation for these three groups and normal feeding for the blank group, the EEG data of all four groups were documented. Following the initial measurement, the GV20 group was treated by acupuncture at GV20 and the sham acupoint group was treated at the sham acupoint, and their EEGs were recorded during the treatment. The frequency of α and β waves of all EEG data were analyzed. Prior to intervention, the GV20 group, the sham acupoint group and the model group exhibited no significant differences in α and β wave frequencies; however, the α wave frequency of these three groups was significantly decreased compared with the blank group (P<0.05), whereas the β wave frequency of these three groups was significantly increased compared with the blank group (P<0.05). This suggested that sleep deprivation affected the frequency of brain waves and enhanced the excitability of the cerebral cortex. During acupuncture treatment with retained needle conditioning, the GV20 group indicated a significant increase in α wave frequency (P<0.05), as well as a significant decrease in β wave frequency compared with prior to treatment (P<0.05), whereas the sham acupoint group exhibited no significant changes. The present findings from a rat model of sleep deprivation suggested that acupuncture treatment at GV20 may reduce the excitability of the brain cortex. Due to its sedative effect, treatment at GV20 may be considered for the treatment of insomnia and related symptoms.

Altered connection properties of important network hubs may be neural risk factors for individuals with primary insomnia

Primary insomnia (PIs) is highly prevalent and can lead to adverse socioeconomic impacts, but the underlying mechanism of its complex brain network impairment remains largely unknown. Functional studies are too few and diverse in methodology, which makes it difficult to glean general conclusions. To answer this question, we first used graph theory-based network analyse, together with seed-based functional connectivity approach, to characterize the topology architecture of whole-brain functional networks associated with PIs. Forty-eight subjects with PIs and 48 age/sex/education-matched good sleepers were recruited. We found PIs is associated with altered connection properties of intra-networks within the executive control network, default mode network and salience network, and inter-network between auditory language comprehension center and executive control network. These complex networks were correlated with negative emotions and insomnia severity in the PIs group. Altered connection properties of these network hubs appeared to be neural risk factors for neuropsychological changes of PIs, and might be used as potential neuroimaging markers to distinguish the PIs from the good sleepers. These findings highlight the role of functional connectivity in the pathophysiology of PIs, and may underlie the neural mechanisms of etiology of PIs.

Effects of Social Defeat Stress on Sleep in Mice

Stress plays a key role in the development of psychiatric disorders and has a negative impact on sleep integrity. In mice, chronic social defeat stress (CSDS) is an ethologically valid model of stress-related disorders but little is known about its effects on sleep regulation. Here, we investigated the immediate and long-term effects of 10 consecutive days of social defeat (SD) on vigilance states in C57Bl/6J male mice. Social behavior was assessed to identify susceptible mice, i.e., mice that develop long-lasting social avoidance, and unsusceptible mice. Sleep-wake stages in mice of both groups were analyzed by means of polysomnographic recordings at baseline, after the first, third, and tenth stress sessions and on the 5th recovery day (R5) following the 10-day CSDS. In susceptible mice, each SD session produced biphasic changes in sleep-wake states that were preserved all along 10-day CSDS. These sessions elicited a short-term enhancement of wake time while rapid eye-movement (REM) sleep was strongly inhibited. Concomitantly, delta power was increased during non REM (NREM) sleep. During the following dark period, an increase in total sleep time, as well as wake fragmentation, were observed after each analyzed SD session. Similar changes were observed in unsusceptible mice. At R5, elevated high-frequency EEG activity, as observed in insomniacs, emerged during NREM sleep in both susceptible and unsusceptible groups suggesting that CSDS impaired sleep quality. Furthermore, susceptible but not unsusceptible mice displayed stress-anticipatory arousal during recovery, a common feature of anxiety disorders. Altogether, our findings show that CSDS has profound impacts on vigilance states and further support that sleep is tightly regulated by exposure to stressful events. They also revealed that susceptibility to chronic psychological stress is associated with heightened arousal, a physiological feature of stress vulnerability.

Effects of Social Defeat Stress on Sleep in Mice

Stress plays a key role in the development of psychiatric disorders and has a negative impact on sleep integrity. In mice, chronic social defeat stress (CSDS) is an ethologically valid model of stress-related disorders but little is known about its effects on sleep regulation. Here, we investigated the immediate and long-term effects of 10 consecutive days of social defeat (SD) on vigilance states in C57Bl/6J male mice. Social behavior was assessed to identify susceptible mice, i.e., mice that develop long-lasting social avoidance, and unsusceptible mice. Sleep-wake stages in mice of both groups were analyzed by means of polysomnographic recordings at baseline, after the first, third, and tenth stress sessions and on the 5th recovery day (R5) following the 10-day CSDS. In susceptible mice, each SD session produced biphasic changes in sleep-wake states that were preserved all along 10-day CSDS. These sessions elicited a short-term enhancement of wake time while rapid eye-movement (REM) sleep was strongly inhibited. Concomitantly, delta power was increased during non REM (NREM) sleep. During the following dark period, an increase in total sleep time, as well as wake fragmentation, were observed after each analyzed SD session. Similar changes were observed in unsusceptible mice. At R5, elevated high-frequency EEG activity, as observed in insomniacs, emerged during NREM sleep in both susceptible and unsusceptible groups suggesting that CSDS impaired sleep quality. Furthermore, susceptible but not unsusceptible mice displayed stress-anticipatory arousal during recovery, a common feature of anxiety disorders. Altogether, our findings show that CSDS has profound impacts on vigilance states and further support that sleep is tightly regulated by exposure to stressful events. They also revealed that susceptibility to chronic psychological stress is associated with heightened arousal, a physiological feature of stress vulnerability.

Subjective-Objective Sleep Discrepancy Is Associated With Alterations in Regional Glucose Metabolism in Patients With Insomnia and Good Sleeper Controls

Objectives

Sleep discrepancies are common in primary insomnia (PI) and include reports of longer sleep onset latency (SOL) than measured by polysomnography (PSG) or "negative SOL discrepancy." We hypothesized that negative SOL discrepancy in PI would be associated with higher relative glucose metabolism during nonrapid eye movement (NREM) sleep in brain networks involved in conscious awareness, including the salience, left executive control, and default mode networks.

Methods

PI (n = 32) and good sleeper controls (GS; n = 30) completed [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) scans during NREM sleep, and relative regional cerebral metabolic rate for glucose (rCMRglc) was measured. Sleep discrepancy was calculated by subtracting PSG-measured SOL on the PET night from corresponding self-report values the following morning. We tested for interactions between group (PI vs. GS) and SOL discrepancy for rCMRglc during NREM sleep using both a region of interest mask and exploratory whole-brain analyses.

Results

Significant group by SOL discrepancy interactions for rCMRglc were observed in several brain regions (pcorrected < .05 for all clusters). In the PI group, more negative SOL discrepancy (self-reported > PSG-measured SOL) was associated with significantly higher relative rCMRglc in the right anterior insula and middle/posterior cingulate during NREM sleep. In GS, more positive SOL discrepancy (self-reported < PSG-measured SOL) was associated with significantly higher relative rCMRglc in the right anterior insula, left anterior cingulate cortex, and middle/posterior cingulate cortex.

Conclusions

Although preliminary, these findings suggest regions of the brain previously shown to be involved in conscious awareness, and the perception of PSG-defined states may also be involved in the phenomena of SOL discrepancy.

REM Sleep Theta Changes in Frequent Nightmare Recallers

Study Objectives

To replicate and expand upon past research by evaluating sleep and wake electroencephalographic spectral activity in samples of frequent nightmare (NM) recallers and healthy controls.

Methods

Computation of spectral activity for sleep (non-REM and REM) and wake electroencephalogram recordings from 18 frequent NM recallers and 15 control participants.

Results

There was higher "slow-theta" (2-5 Hz) for NM recallers than for controls during wake, non-REM sleep and REM sleep. Differences were clearest for frontal and central derivations and for REM sleep cycles 2-4. There was also higher beta activity during NREM sleep for NM recallers. Findings partially replicate past research by demonstrating higher relative "slow-theta" (3-4Hz) for NM recallers than for controls.

Conclusions

Findings are consistent with a neurocognitive model of nightmares that stipulates cross-state anomalies in emotion processing in NM-prone individuals.

Association of symptoms of insomnia and sleep parameters among kidney transplant recipients

OBJECTIVE

Insomnia complaints are frequent among kidney transplant (kTx) recipients and are associated with fatigue, depression, lower quality of life and increased morbidity. However, it is not known if subjective insomnia symptoms are associated with objective parameters of sleep architecture. Thus, we analyze the association between sleep macrostructure and EEG activity versus insomnia symptoms among kTx recipients.

METHODS

Participants (n₁=100) were selected from prevalent adult transplant recipients (n₀=1214) followed at a single institution. Insomnia symptoms were assessed by the Athens Insomnia Scale (AIS) and standard overnight polysomnography was performed. In a subgroup of patients (n₂=56) sleep microstructure was also analyzed with power spectral analysis.

RESULTS

In univariable analysis AIS score was not associated with sleep macrostructure parameters (sleep latency, total sleep time, slow wave sleep, wake after sleep onset), nor with NREM and REM beta or delta activity in sleep microstructure. In multivariable analysis after controlling for covariables AIS score was independently associated with the proportion of slow wave sleep (β=0.263; CI: 0.026-0.500) and REM beta activity (β=0.323; CI=0.041-0.606) (p<0.05 for both associations).

CONCLUSIONS

Among kTx recipients the severity of insomnia symptoms is independently associated with higher proportion of slow wave sleep and increased beta activity during REM sleep but not with other parameters sleep architecture. The results suggest a potential compensatory sleep protective mechanism and a sign of REM sleep instability associated with insomnia symptoms among this population.

Similar polysomnographic pattern in primary insomnia and major depression with objective insomnia: a sign of common pathophysiology?

BACKGROUND

Our aim is to verify empirically the existence of a major depressed subgroup with a similar polysomnographic pattern as primary insomnia, including at rapid eye movement sleep level.

METHODS

The polysomnographic data from 209 untreated individuals (30 normative, 84 primary insomnia sufferers, and 95 major depressed patients with objective insomnia) who were recruited retrospectively from the Erasme hospital database were studied for the whole night and thirds of the night.

RESULTS

Primary insomnia sufferers and major depressed patients with objective insomnia exhibit a similar polysomnographic pattern both for the whole night (excess of wake after sleep onset, deficit in slow-wave sleep/rapid eye movement sleep, and non-shortened rapid eye movement latency) and thirds of the night (excess of wake after sleep onset at first and last third, deficit in slow-wave sleep in first third, and deficit in rapid eye movement sleep in first and last third), including at rapid eye movement sleep level.

CONCLUSION

In our study, we demonstrated that major depressed patients with objective insomnia showed a similar polysomnographic pattern as primary insomnia, including at rapid eye movement sleep level, which supports the hypothesis of a common pathophysiology that could be hyperarousal. This opens new avenues for understanding the pathophysiology of major depression with objective insomnia.

Hyperarousal during sleep in untreated primary insomnia sufferers: A polysomnographic study

Because some evidence favors the hyperarousal model of insomnia, we sought to learn more about the dynamics of this phenomenon during sleep. Polysomnographic data from 30 normative subjects and 86 untreated primary insomnia sufferers recruited from the database of the sleep laboratory were studied for whole nights and in terms of thirds of the night. Untreated primary insomnia sufferers had an increased sleep latency and excess of WASO, together with a deficit in REM and NREM sleep during the entire night. In terms of thirds of the night, they presented a major excess of WASO during the first and last thirds of the night but an excess of lesser importance during the middle third. A deficit in SWS was found during the first third of the night, but for REM, the deficit was present during both the first and last thirds. Primary insomnia sufferers had no SWS or REM deficit during the second third of the night. We found that the hyperarousal phenomenon occurs mainly during the sleep-onset period of the first and last thirds of the night and is less important during the middle third. These results open new avenues for understanding the pathophysiology of primary insomnia.

Slow-Wave Sleep Estimation for Healthy Subjects and OSA Patients Using R-R Intervals

We developed an automatic slow-wave sleep (SWS) detection algorithm that can be applied to groups of healthy subjects and patients with obstructive sleep apnea (OSA). This algorithm detected SWS based on autonomic activations derived from the heart rate variations of a single sensor. An autonomic stability, which is an SWS characteristic, was evaluated and quantified using R-R intervals from an electrocardiogram (ECG). The thresholds and the heuristic rule to determine SWS were designed based on the physiological backgrounds for sleep process and distribution across the night. The automatic algorithm was evaluated based on a fivefold cross validation using data from 21 healthy subjects and 24 patients with OSA. An epoch-by-epoch (30 s) analysis showed that the overall Cohen's kappa, accuracy, sensitivity, and specificity of our method were 0.56, 89.97%, 68.71%, and 93.75%, respectively. SWS-related information, including SWS duration (min) and percentage (%), were also calculated. A significant correlation in these parameters was found between automatic and polysomnography scorings. Compared with similar methods, the proposed algorithm convincingly discriminated SWS from non-SWS. The simple method using only R-R intervals has the potential to be utilized in mobile and wearable devices that can easily measure this information. Moreover, when combined with other sleep staging methods, the proposed method is expected to be applicable to long-term sleep monitoring at home and ambulatory environments.

Neuroligin 3 R451C mutation alters electroencephalography spectral activity in an animal model of autism spectrum disorders

Human studies demonstrate that sleep impairment is a concurrent comorbidity of autism spectrum disorders (ASD), but its etiology remains largely uncertain. One of the prominent theories of ASD suggests that an imbalance in synaptic excitation/inhibition may contribute to various aspects of ASD, including sleep impairments. Following the identification of Nlgn3^R451C mutation in patients with ASD, its effects on synaptic transmission and social behaviours have been examined extensively in the mouse model. However, the contributory role of this mutation to sleep impairments in ASD remains unknown. In this study, we showed that Nlgn3^R451C knock-in mice, an established genetic model for ASD, exhibited normal duration and distribution of sleep/wake states but significantly altered electroencephalography (EEG) power spectral profiles for wake and sleep.

Neurophysiological correlates of suicidal ideation in major depressive disorder: Hyperarousal during sleep

BACKGROUND

Suicide is a major public health concern, and a barrier to reducing the suicide rate is the lack of objective predictors of risk. The present study considers whether quantitative sleep electroencephalography (EEG) may be a neurobiological correlate of suicidal ideation.

METHODS

Participants included 84 (45 female, mean age=26.6) adults diagnosed with major depressive disorder (MDD). The item that measures thoughts of death or suicide on the Quick Inventory of Depressive Symptomatology (QIDS) was used to classify 47 participants as low suicidal ideation (24 females, mean age=26.1) and 37 as high suicidal ideation (21 females, mean age=27.3). Data were obtained from archival samples collected at the University of Michigan and University of Texas Southwestern Medical Center between 2004 and 2012. Sleep EEG was quantified using power spectral analysis, and focused on alpha, beta, and delta frequencies.

RESULTS

Results indicated that participants with high compared to low suicidal ideation experienced 1) increased fast frequency activity, 2) decreased delta activity, and 3) increased alpha-delta sleep after adjusting for age, sex, depression, and insomnia symptoms.

LIMITATIONS

Limitations include the exclusion of imminent suicidal intent, a single suicidal ideation item, and cross-sectional archival data.

CONCLUSIONS

This is one of the first studies to provide preliminary support that electrophysiological brain activity during sleep is associated with increased suicidal ideation in MDD, and may point toward central nervous system (CNS) hyperarousal during sleep as a neurobiological correlate of suicidal ideation.

Hyperarousal and Beyond: New Insights to the Pathophysiology of Insomnia Disorder through Functional Neuroimaging Studies

Neuroimaging studies have produced seemingly contradictory findings in regards to the pathophysiology of insomnia. Although most study results are interpreted from the perspective of a "hyperarousal" model, the aggregate findings from neuroimaging studies suggest a more complex model is needed. We provide a review of the major findings from neuroimaging studies, then discuss them in relation to a heuristic model of sleep-wake states that involves three major factors: wake drive, sleep drive, and level of conscious awareness. We propose that insomnia involves dysregulation in these factors, resulting in subtle dysregulation of sleep-wake states throughout the 24 h light/dark cycle.

Task switching in older adults with and without insomnia

BACKGROUND

Task-switching deficits are common in older adults and in those with insomnia. Such deficits may be driven by difficulties with sleep continuity and dampened homeostatic sleep drive.

OBJECTIVE

To identify the aspects of task switching affected by insomnia and its treatment, and to determine whether such effects are associated with sleep continuity and homeostatic sleep drive.

METHODS

Polysomnographic sleep and task switching were tested in healthy older adults aged 60-93 years with insomnia (n = 48) and normal sleeping controls (n = 51). Assessments were repeated in the insomnia group after eight weeks of cognitive behavioral treatment for insomnia. Sleep measures included wake after sleep onset (WASO) and quantitative indices of homeostatic sleep drive (delta power during nonrapid eye movement [NREM] sleep and the ratio of delta power during the first and second NREM periods). A cued task-switching paradigm instructed participants to perform one of two tasks with varying preparatory cue-target intervals, manipulating task alternation, task repetition, and task preparation.

RESULTS

The effect of preparatory cues on accuracy was diminished in the insomnia group compared with that in controls. Across the two groups, a stronger effect of preparatory cues was associated with a higher delta sleep ratio. Following insomnia treatment, task-repetition accuracy significantly improved. This improvement was associated with improvements in WASO. There were no group or treatment effects on response time or task alternation accuracy.

CONCLUSIONS

Effects of insomnia diagnosis and treatment apply to conditions that depend on the maintenance of a task set, rather than a domain general effect across task switching. Such effects are associated with homeostatic sleep drive and sleep continuity.

Gender Differences in Regional Brain Activity in Patients with Chronic Primary Insomnia: Evidence from a Resting-State fMRI Study

STUDY OBJECTIVES

To explore the regional brain activities in patients with chronic primary insomnia (PCPIs) and their sex differences.

METHODS

Forty-two PCPIs (27 females, 15 males) and 42 good sleepers (GSs; 24 females, 18 males) were recruited. Six PCPIs (3 males, 3 females) were scanned twice by MRI to examine the test-retest reliability. Amplitude of low frequency fluctuation (ALFF) method was used to assess the local brain features. The mean signal values of the different ALFF areas were analyzed with a receiver operating characteristic (ROC) curve. Simple linear regression analysis was performed to investigate the relationships between clinical features and different brain areas.

RESULTS

Both female and male PCPIs showed higher ALFF in the temporal lobe and occipital lobe, especially in female PCPIs. Female PCPIs had lower ALFF in the bilateral cerebellum posterior lobe, left dorsolateral prefrontal cortex, and bilateral limbic lobe; however, male PCPIs showed lower ALFF in the left occipital gyrus. The mean signal value of the cerebellum in female PCPIs showed negative correlations with negative emotions. Compared with male PCPIs, female PCPIs showed higher ALFF in the bilateral middle temporal gyrus and lower ALFF in the left limbic lobe. The different areas showed high test-retest stability (Clusters of contiguous volumes ≥ 1080 mm(3) with an intraclass correlation coefficient ≥ 0.80) and high degree of sensitivity and specificity.

CONCLUSIONS

Female PCPIs showed more regional brain differences with higher and lower ALFF responses than male PCPIs. However, they shared analogous excessive hyperarousal mechanism and wide variations in aberrant brain areas.

Sleep disturbances in adolescents with ADHD: A systematic review and framework for future research

BACKGROUND

Biological mechanisms underlying symptom and prognostic heterogeneity in Attention-Deficit/Hyperactivity Disorder (ADHD) are unclear. Sleep impacts neurocognition and daytime functioning and is disrupted in ADHD, yet little is known about sleep in ADHD during adolescence, a period characterized by alterations in sleep, brain structure, and environmental demands as well as diverging ADHD trajectories.

METHODS

A systematic review identified studies published prior to August 2016 assessing sleep in adolescents (aged 10-19years) with ADHD or participating in population-based studies measuring ADHD symptoms.

RESULTS

Twenty-five studies were identified (19 subjective report, 6 using actigraphy/polysomnography). Findings are mixed but overall suggest associations between sleep disturbances and 1) ADHD symptoms in the population and 2) poorer clinical, neurocognitive, and functional outcomes among adolescents with ADHD. Common limitations of studies included small or non-representative samples, non-standardized sleep measures, and cross-sectional methodology.

CONCLUSIONS

Current data on sleep in adolescent ADHD are sparse and limited by methodological concerns. Future studies are critical for clarifying a potential role of sleep in contributing to heterogeneity of ADHD presentation and prognosis. Potential mechanisms by which sleep disturbances during adolescence may contribute to worsened symptom severity and persistence of ADHD into adulthood and an agenda to guide future research are discussed.

EEG spectral analysis of NREM sleep in a large sample of patients with insomnia and good sleepers: effects of age, sex and part of the night

Previous studies of the differences between patients with insomnia and good sleepers with regard to quantitative electroencephalographic measures have mostly utilized small samples and consequently had limited ability to account for potentially important confounding factors of age, sex and part of the night. We conducted a power spectral analysis using a large database of sleep electroencephalographic recordings to evaluate differences between patients with insomnia (N = 803) and good sleepers (N = 811), while simultaneously accounting for these factors and their interaction. Comparisons of power as a function of age and part of the night were made between cohorts (patients with insomnia versus good sleepers) by sex. Absolute power in the delta, theta and sigma bands declined with age for both females and males. Females had significantly greater power than males at all ages, and for each band, cohort and part of the night. These sex differences were much greater than differences between patients with insomnia and good sleepers. Compared with good sleepers, patients with insomnia under age 40-45 years had reduced delta band power during Part 1 of the night. Females with insomnia over age 45 years had increased delta and theta band power in Parts 2 and 3 of the night, and males with insomnia under age 40 years had reduced theta power in Part 1. Females with insomnia had increased beta2 power in all parts of the night, and males with insomnia had reduced alpha power during all parts of the night. Relative power (the proportion that an individual frequency band contributes to the total power) decreased in the delta band and increased in all other bands with age for both cohorts, sexes and all parts of the night. This analysis provides a unique resource for quantitative information on the differences in power spectra between patients with insomnia and good sleepers accounting for age, sex and part of the night.

Neurophysiologic Correlates of Post-stroke Mood and Emotional Control

OBJECTIVE

Emotional disturbance is a common complication of stroke significantly affecting functional recovery and quality of life. Identifying relevant neurophysiologic markers associated with post-stroke emotional disturbance may lead to a better understanding of this disabling condition, guiding the diagnosis, development of new interventions and the assessments of treatment response.

METHODS

Thirty-five subjects with chronic stroke were enrolled in this study. The emotion sub-domain of Stroke Impact Scale (SIS-Emotion) was used to assess post-stroke mood and emotional control. The relation between SIS-Emotion and neurophysiologic measures was assessed by using covariance mapping and univariate linear regression. Multivariate analyses were conducted to identify and adjust for potential confounders. Neurophysiologic measures included power asymmetry and coherence assessed by electroencephalography (EEG); and motor threshold, intracortical inhibition (ICI) and intracortical facilitation (ICF) measured by transcranial magnetic stimulation (TMS).

RESULTS

Lower scores on SIS-Emotion was associated with (1) frontal EEG power asymmetry in alpha and beta bands, (2) central EEG power asymmetry in alpha and theta bands, and (3) lower inter-hemispheric coherence over frontal and central areas in alpha band. SIS-Emotion also correlated with higher ICF and MT in the unlesioned hemisphere as measured by TMS.

CONCLUSIONS

To our knowledge, this is the first study using EEG and TMS to index neurophysiologic changes associated with post-stroke mood and emotional control. Our results suggest that inter-hemispheric imbalance measured by EEG power and coherence, as well as an increased ICF in the unlesioned hemisphere measured by TMS might be relevant markers associated with post-stroke mood and emotional control which can guide future studies investigating new diagnostic and treatment modalities in stroke rehabilitation.

Age-Related Reduction of Recovery Sleep and Arousal Threshold in Drosophila

STUDY OBJECTIVES

Physiological studies show that aging affects both sleep quality and quantity in humans, and sleep complaints increase with age. Along with knowledge about the negative effects of poor sleep on health, understanding the enigmatic relationship between sleep and aging is important. Because human sleep is similar to Drosophila (fruit fly) sleep in many ways, we addressed the effects of aging on sleep in this model organism.

METHODS

Baseline sleep was recorded in five different Drosophila genotypes raised at either 21°C or 25°C. The amount of sleep recovered was then investigated after a nighttime of sleep deprivation (12 h) and after chronic sleep deprivation (3 h every night for multiple nights). Finally, the effects of aging on arousal, namely, sensitivity to neuronal and mechanical stimuli, were studied.

RESULTS

We show that fly sleep is affected by age in a manner similar to that of humans and other mammals. Not only do older flies of several genotypes have more fragmented sleep and reduced total sleep time compared to young flies, but older flies also fail to recover as much sleep after sleep deprivation. This suggests either lower sleep homeostasis and/or a failure to properly recover sleep. Older flies also show a decreased arousal threshold, i.e., an increased response to neuronal and mechanical wake-promoting stimuli. The reduced threshold may either reflect or cause the reduced recovery sleep of older flies compared to young flies after sleep deprivation.

CONCLUSIONS

Further studies are certainly needed, but we suggest that the lower homeostatic sleep drive of older flies causes their decreased arousal threshold.

Sleep Spindles Characteristics in Insomnia Sufferers and Their Relationship with Sleep Misperception

Cortical hyperarousal is higher in insomnia sufferers (INS) than in good sleepers (GS) and could be related to an alteration in sleep protection mechanisms, like reduced density or altered characteristics in sleep spindles. The deficient sleep protection mechanisms might in turn enhance underestimation of sleep. This study's objective was to document sleep spindles characteristics in INS compared with GS and to investigate their potential role in sleep consolidation and misperception. Seventeen individuals with paradoxical insomnia (PARA-I), 24 individuals with psychophysiological insomnia (PSY-I), and 29 GS completed four consecutive polysomnographic nights in laboratory. Sleep spindles were detected automatically during stage 2 and SWS (3-4) on night 3. Number, density, duration, frequency, and amplitude of sleep spindles were calculated. A misperception index was used to determine the degree of discrepancy between subjective and objective total sleep times. Kruskal-Wallis H tests and post hoc tests revealed that PARA-I had significantly shorter sleep spindles than GS but that PSY-I and GS did not differ on spindles length. A standard multiple regression model revealed that neither sleep spindles characteristics nor objective sleep measures were predictive of sleep misperception. A longer duration of spindles could reflect a higher gating process but this hypothesis still needs to be confirmed in replication studies.

Insomnia is Associated with Cortical Hyperarousal as Early as Adolescence

STUDY OBJECTIVES

To examine whether insomnia is associated with spectral electroencephalographic (EEG) dynamics in the beta (15-35Hz) range during sleep in an adolescent general population sample.

METHODS

A case-control sample of 44 adolescents from the Penn State Child Cohort underwent a 9-h polysomnography, clinical history and physical examination. We examined low-beta (15-25 Hz) and high-beta (25-35 Hz) relative power at central EEG derivations during sleep onset latency (SOL), sleep onset (SO), non-rapid eye movement (NREM) sleep, and wake after sleep onset (WASO).

RESULTS

Compared to controls (n = 21), individuals with insomnia (n = 23) showed increased SOL and WASO and decreased sleep duration and efficiency, while no differences in sleep architecture were found. Insomniacs showed increased low-beta and high-beta relative power during SOL, SO, and NREM sleep as compared to controls. High-beta relative power was greater during all sleep and wake states in insomniacs with short sleep duration as compared to individuals with insomnia with normal sleep duration.

CONCLUSIONS

Adolescent insomnia is associated with increased beta EEG power during sleep, which suggests that cortical hyperarousal is present in individuals with insomnia as early as adolescence. Interestingly, cortical hyperarousal is greatest in individuals with insomnia with short sleep duration and may explain the sleep complaints of those with normal sleep duration. Disturbed cortical networks may be a shared mechanism putting individuals with insomnia at risk of psychiatric disorders.

Regional Patterns of Elevated Alpha and High-Frequency Electroencephalographic Activity during Nonrapid Eye Movement Sleep in Chronic Insomnia: A Pilot Study

STUDY OBJECTIVES

To examine nonrapid eye movement (NREM) sleep in insomnia using high-density electroencephalography (EEG).

METHODS

All-night sleep recordings with 256 channel high-density EEG were analyzed for 8 insomnia subjects (5 females) and 8 sex and age-matched controls without sleep complaints. Spectral analyses were conducted using unpaired t-tests and topographical differences between groups were assessed using statistical non-parametric mapping. Five minute segments of deep NREM sleep were further analyzed using sLORETA cortical source imaging.

RESULTS

The initial topographic analysis of all-night NREM sleep EEG revealed that insomnia subjects had more high-frequency EEG activity (> 16 Hz) compared to good sleeping controls and that the difference between groups was widespread across the scalp. In addition, the analysis also showed that there was a more circumscribed difference in theta (4-8 Hz) and alpha (8-12 Hz) power bands between groups. When deep NREM sleep (N3) was examined separately, the high-frequency difference between groups diminished, whereas the higher regional alpha activity in insomnia subjects persisted. Source imaging analysis demonstrated that sensory and sensorimotor cortical areas consistently exhibited elevated levels of alpha activity during deep NREM sleep in insomnia subjects relative to good sleeping controls.

CONCLUSIONS

These results suggest that even during the deepest stage of sleep, sensory and sensorimotor areas in insomnia subjects may still be relatively active compared to control subjects and to the rest of the sleeping brain.

Spindle Oscillations in Sleep Disorders: A Systematic Review

Measurement of sleep microarchitecture and neural oscillations is an increasingly popular technique for quantifying EEG sleep activity. Many studies have examined sleep spindle oscillations in sleep-disordered adults; however reviews of this literature are scarce. As such, our overarching aim was to critically review experimental studies examining sleep spindle activity between adults with and without different sleep disorders. Articles were obtained using a systematic methodology with a priori criteria. Thirty-seven studies meeting final inclusion criteria were reviewed, with studies grouped across three categories: insomnia, hypersomnias, and sleep-related movement disorders (including parasomnias). Studies of patients with insomnia and sleep-disordered breathing were more abundant relative to other diagnoses. All studies were cross-sectional. Studies were largely inconsistent regarding spindle activity differences between clinical and nonclinical groups, with some reporting greater or less activity, while many others reported no group differences. Stark inconsistencies in sample characteristics (e.g., age range and diagnostic criteria) and methods of analysis (e.g., spindle bandwidth selection, visual detection versus digital filtering, absolute versus relative spectral power, and NREM2 versus NREM3) suggest a need for greater use of event-based detection methods and increased research standardization. Hypotheses regarding the clinical and empirical implications of these findings, and suggestions for potential future studies, are also discussed.

Alpha-wave frequency characteristics in health and insomnia during sleep

Appearances of alpha waves in the sleep electrencephalogram indicate physiological, brief states of awakening that lie in between wakefulness and sleep. These microstates may also cause the loss in sleep quality experienced by individuals suffering from insomnia. To distinguish such pathological awakenings from physiological ones, differences in alpha-wave characteristics between transient awakening and wakefulness observed before the onset of sleep were studied. In polysomnographic datasets of sleep-healthy participants (n = 18) and patients with insomnia (n = 10), alpha waves were extracted from the relaxed, wake state before sleep onset, wake after sleep-onset periods and arousals of sleep. In these, alpha frequency and variability were determined as the median and standard deviation of inverse peak-to-peak intervals. Before sleep onset, patients with insomnia showed a decreased alpha variability compared with healthy participants (P < 0.05). After sleep onset, both groups showed patterns of decreased alpha frequency that was lower for wake after sleep-onset periods of shorter duration. For patients with insomnia, alpha variability increased for short wake after sleep-onset periods. Major differences between the two groups were encountered during arousal. In particular, the alpha frequency in patients with insomnia rebounded to wake levels, while the frequency in healthy participants remained at the reduced level of short wake after sleep-onset periods. Reductions in alpha frequency during wake after sleep-onset periods may be related to the microstate between sleep and wakefulness that was described for such brief awakenings. Reduced alpha variability before sleep may indicate a dysfunction of the alpha generation mechanism in insomnia. Alpha characteristics may also prove valuable in the study of other sleep and attention disorders.

Waking EEG signs of non-restoring sleep in primary insomnia patients

OBJECTIVE

Subjective feelings of insufficient and non-restorative sleep are core symptoms of primary insomnia. Sleep has a restorative effect on next-day waking EEG activity, whereas sleep loss has non-restorative effects in good sleepers. We proposed to explore waking EEG activity in primary insomniacs the evening before, and the morning after, a night of sleep, in order to detect signs of morning hyper-arousal and non-restoring sleep that might explain the subjective feelings despite the absence of objective signs in polysomnography.

METHOD

Pre-sleep (10 pm) and post-sleep (10 am) waking EEG activity was analyzed in 10 non-medicated primary insomniacs and matched control subjects. Beta and Gamma absolute power and EEG temporal coupling were obtained. Participants also evaluated subjective sleep quantity and quality.

RESULTS

Insomnia patients evaluated their sleep as non-restorative and insufficient. Compared to pre-sleep, during post-sleep control subjects exhibited significantly decreased Beta and Gamma power and reduced synchronization among anterior and posterior regions, consistent with restoring effects of sleep. Insomnia patients showed no beneficial effects of sleep on these EEG parameters.

CONCLUSION

Insomniacs are hyper-aroused during morning wakefulness and they do not benefit from preceding sleep.

SIGNIFICANCE

Our study adds new knowledge to our understanding of the physiopathology of insomnia.

Randomised clinical trial of the effects of prolonged-release melatonin, temazepam and zolpidem on slow-wave activity during sleep in healthy people

Current pharmacological treatments for insomnia include benzodiazepine and non-benzodiazepine hypnotics targeting γ-aminobutyric acid (GABA)A receptors, as well as agonists of the melatonin receptors MT1 and MT2. Melatonin, temazepam and zolpidem are thought to exert their effect through different mechanisms of action, but whether this leads to differential effects on electroencephalogram (EEG) power spectra during sleep in middle-aged people is currently not known. To establish whether the effects of prolonged-release melatonin (2 mg) on the nocturnal sleep EEG are different to those of temazepam (20 mg) and zolpidem (10 mg). Sixteen healthy men and women aged 55-64 years participated in a double-blind, placebo-controlled, four-way cross-over trial. Nocturnal sleep was assessed with polysomnography and spectral analysis of the EEG. The effects of single oral doses of prolonged-release melatonin, temazepam and zolpidem on EEG slow-wave activity (SWA, 0.75-4.5 Hz) and other frequencies during nocturnal non-rapid eye movement (NREM) sleep were compared. In an entire night analysis prolonged-release melatonin did not affect SWA, whereas temazepam and zolpidem significantly reduced SWA compared with placebo. Temazepam significantly reduced SWA compared with prolonged-release melatonin. Prolonged-release melatonin only reduced SWA during the first third of the night compared with placebo. These data show that the effects of prolonged-release melatonin on the nocturnal sleep EEG are minor and are different from those of temazepam and zolpidem; this is likely due to the different mechanisms of action of the medications.

The pathophysiology of insomnia

Insomnia disorder is characterized by chronic dissatisfaction with sleep quantity or quality that is associated with difficulty falling asleep, frequent nighttime awakenings with difficulty returning to sleep, and/or awakening earlier in the morning than desired. Although progress has been made in our understanding of the nature, etiology, and pathophysiology of insomnia, there is still no universally accepted model. Greater understanding of the pathophysiology of insomnia may provide important information regarding how, and under what conditions, the disorder develops and is maintained as well as potential targets for prevention and treatment. The aims of this report are (1) to summarize current knowledge on the pathophysiology of insomnia and (2) to present a model of the pathophysiology of insomnia that considers evidence from various domains of research. Working within several models of insomnia, evidence for the pathophysiology of the disorder is presented across levels of analysis, from genetic to molecular and cellular mechanisms, neural circuitry, physiologic mechanisms, sleep behavior, and self-report. We discuss the role of hyperarousal as an overarching theme that guides our conceptualization of insomnia. Finally, we propose a model of the pathophysiology of insomnia that integrates the various types of evidence presented.

Trauma-induced insomnia: A novel model for trauma and sleep research

Traumatic events have been increasingly recognized as important precipitants of clinically significant insomnia. Trauma is an extreme form of stressful life event that generates a sustained neurobiological response triggering the onset and maintenance of insomnia. Trauma may disrupt the normal sleep-wake regulatory mechanism by sensitizing the central nervous system's arousal centers, leading to pronounced central and physiological hyperarousal. The central concept of hyperarousal has been linked to both the pathogenesis of insomnia and to the neurobiological changes in the aftermath of traumatic events, and may be a neurobiological commonality underlying trauma and insomnia. This paper presents evidence for trauma-induced insomnia and advances a model of it as an important nosological and neurobiological entity. Trauma-induced insomnia may occur in the absence of full-blown posttraumatic stress disorder (PTSD), and may also be a precursor of subsequent PTSD development. Converging lines of evidence from the neuroscience of insomnia with the neurobiology and psychophysiology of stress, fear, trauma and PTSD will be integrated to advance understanding of the condition. Preclinical and clinical stress and fear paradigms have informed the neurobiological pathways mediating the production of insomnia by trauma. Elucidating the underlying neurobiological substrates can establish novel biological markers to identify persons at risk for the condition, and help optimize treatment of the trauma-insomnia interface. Early identification and treatment of trauma-induced insomnia may prevent the development of PTSD, as well as other important sequelae such as depression, substance dependence, and other medical conditions.

Decreased delta sleep ratio and elevated alpha power predict vulnerability to depression during interferon-alpha treatment

OBJECTIVE

Although poor sleep accompanies depression, it is unknown which specific sleep abnormalities precede depression. This is similarly the case for depression developing during interferon-α (IFN-α) therapy. Because vulnerability becomes evident in those who slept poorly before IFN-α, we prospectively determined which specific aspect of sleep could predict subsequent depression.

METHODS

Two nights of polysomnography with quantitative electroencephalogram (EEG) were obtained in 24 adult, euthymic subjects--all subsequently treated with IFN-α for hepatitis C. Every 2 weeks, a Beck Depression Inventory-II (BDI-II) score was obtained, and the maximal increase in BDI-II from pre-treatment baseline--excluding the sleep question--was determined.

RESULTS

The delta sleep ratio (DSR; an index of early-night restorative delta power) was inversely associated with BDI-II increases (p<0.01), as was elevated alpha power (8-12 Hz; p<0.001). Both delta (0.5-4 Hz) and alpha power exhibited high between-night correlations (r=0.83 and 0.92, respectively). In mixed-effect repeated-measure analyses, there was an interaction between alpha power and DSR (p<0.001)--subjects with low alpha power and elevated DSR were resilient to developing depression. Most other sleep parameters--including total sleep time and percentage of time in slow wave sleep--were not associated with subsequent changes in depression.

CONCLUSIONS

Both high DSR and low alpha power may be specific indices of resilience. As most other aspects of sleep were not associated with resilience or vulnerability, sleep interventions to prevent depression may need to specifically target these specific sleep parameters.

Information processing during sleep and stress-related sleep vulnerability

AIMS

Previous studies showed enhanced attention and decreased inhibitory processes during early non-rapid eye movement sleep in primary insomnia patients, as measured by event-related potentials. The current study aims to examine information processing during sleep in non-insomniac individuals with high vulnerability (HV) to stress-related sleep disturbances.

METHODS

Twenty-seven non-insomniac individuals were recruited, 14 with low vulnerability and 13 with HV. After passing a screening interview and polysomnographic recording, subjects came to the sleep laboratory for 2 nights (a baseline night and a stress-inducing night) for event-related potentials recordings.

RESULTS

The HV group demonstrated shorter P2 latency during the first 5 min of stage 2 sleep and higher P900 amplitudes under the stress condition during slow-wave sleep, which indicates an increased level of inhibitory processes. In addition, they had shorter N1 latencies during slow-wave sleep that could indicate an elevated level of attention processing during deep sleep.

CONCLUSIONS

Unlike patients with chronic insomnia, individuals with high sleep vulnerability to stress show a compensatory process that may prevent external stimulation from interfering with their sleep. This may be one of the factors preventing their acute sleep disturbances from becoming chronic problems.

Specific EEG sleep pattern in the prefrontal cortex in primary insomnia

OBJECTIVE

To assess the specific prefrontal activity in comparison to those in the other main cortical areas in primary insomnia patients and in good sleepers.

METHODS

Fourteen primary insomnia patients and 11 good sleepers were included in the analysis. Participants completed one night of polysomnography in the sleep lab. Power spectra were calculated during the NREM (Non-rapid eyes movements) and the REM (Rapid eyes movements) sleep periods at prefrontal, occipital, temporal and central electrode positions.

RESULTS

During the NREM sleep, the power spectra did not differ between groups in the prefrontal cortex; while primary insomnia patients exhibited a higher beta power spectrum and a lower delta power spectrum compared to good sleepers in other areas. During the REM sleep, the beta1 power spectrum was lower in the prefrontal cortex in primary insomnia patients compared to good sleepers; while no significant difference between groups was obtained for the other areas.

CONCLUSIONS

The present study shows a specific prefrontal sleep pattern during the whole sleep period. In addition, we suggest that primary insomnia patients displayed a dysfunction in the reactivation of the limbic system during the REM sleep and we give additional arguments in favor of a sleep-protection mechanism displayed by primary insomnia patients.