Effect of flurazepam on sleep spindles and K-complexes

Sleep spindle architecture associated with distinct clinical phenotypes in older adults at risk for dementia

Sleep spindles are a hallmark of non-REM sleep and play a fundamental role in memory consolidation. Alterations in these spindles are emerging as sensitive biomarkers for neurodegenerative diseases of ageing. Understanding the clinical presentations associated with spindle alterations may help to elucidate the functional role of these distinct electroencephalographic oscillations and the pathophysiology of sleep and neurodegenerative disorders. Here, we use a data-driven approach to examine the sleep, memory and default mode network connectivity phenotypes associated with sleep spindle architecture in older adults (mean age = 66 years). Participants were recruited from a specialist clinic for early diagnosis and intervention for cognitive decline, with a proportion showing mild cognitive deficits on neuropsychological testing. In a sample of 88 people who underwent memory assessment, overnight polysomnography and resting-state fMRI, a k-means cluster analysis was applied to spindle measures of interest: fast spindle density, spindle duration and spindle amplitude. This resulted in three clusters, characterised by preserved spindle architecture with higher fast spindle density and longer spindle duration (Cluster 1), and alterations in spindle architecture (Clusters 2 and 3). These clusters were further characterised by reduced memory (Clusters 2 and 3) and nocturnal hypoxemia, associated with sleep apnea (Cluster 3). Resting-state fMRI analysis confirmed that default mode connectivity was related to spindle architecture, although directionality of this relationship differed across the cluster groups. Together, these results confirm a diversity in spindle architecture in older adults, associated with clinically meaningful phenotypes, including memory function and sleep apnea. They suggest that resting-state default mode connectivity during the awake state can be associated with sleep spindle architecture; however, this is highly dependent on clinical phenotype. Establishing relationships between clinical and neuroimaging features and sleep spindle alterations will advance our understanding of the bidirectional relationships between sleep changes and neurodegenerative diseases of ageing.

Reconsidering sleep perception in insomnia: from misperception to mismeasurement

So-called 'sleep misperception' refers to a phenomenon in which individuals have the impression of sleeping little or not at all despite normal objective measures of sleep. It is unknown whether this subjective-objective mismatch truly reflects an abnormal perception of sleep, or whether it results from the inability of standard sleep recording techniques to capture 'wake-like' brain activity patterns that could account for feeling awake during sleep. Here, we systematically reviewed studies reporting sleep macro- and microstructural, metabolic, and mental correlates of sleep (mis)perception. Our findings suggest that most individuals tend to accurately estimate their sleep duration measured with polysomnography (PSG). In good sleepers, feeling awake during sleep is the rule at sleep onset, remains frequent in the first non-rapid eye movement sleep cycle and almost never occurs in rapid eye movement (REM) sleep. In contrast, there are patients with insomnia who consistently underestimate their sleep duration, regardless of how long they sleep. Unlike good sleepers, they continue to feel awake after the first sleep cycle and importantly, during REM sleep. Their mental activity during sleep is also more thought-like. Initial studies based on standard PSG parameters largely failed to show consistent differences in sleep macrostructure between these patients and controls. However, recent studies assessing sleep with more refined techniques have revealed that these patients show metabolic and microstructural electroencephalography changes that likely reflect a shift towards greater cortical activation during sleep and correlate with feeling awake. We discuss the significance of these correlates and conclude with open questions and possible ways to address them.

Alcohol use disorder and sleep disturbances: a feed-forward allostatic framework

The development of alcohol use disorder (AUD) involves binge or heavy drinking to high levels of intoxication that leads to compulsive intake, the loss of control in limiting intake, and a negative emotional state when alcohol is removed. This cascade of events occurs over an extended period within a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. These three heuristic stages map onto the dysregulation of functional domains of incentive salience/habits, negative emotional states, and executive function, mediated by the basal ganglia, extended amygdala, and frontal cortex, respectively. Sleep disturbances, alterations of sleep architecture, and the development of insomnia are ubiquitous in AUD and also map onto the three stages of the addiction cycle. During the binge/intoxication stage, alcohol intoxication leads to a faster sleep onset, but sleep quality is poor relative to nights when no alcohol is consumed. The reduction of sleep onset latency and increase in wakefulness later in the night may be related to the acute effects of alcohol on GABAergic systems that are associated with sleep regulation and the effects on brain incentive salience systems, such as dopamine. During the withdrawal/negative affect stage, there is a decrease in slow-wave sleep and some limited recovery in REM sleep when individuals with AUD stop drinking. Limited recovery of sleep disturbances is seen in AUD within the first 30 days of abstinence. The effects of withdrawal on sleep may be related to the loss of alcohol as a positive allosteric modulator of GABAA receptors, a decrease in dopamine function, and the overactivation of stress neuromodulators, including hypocretin/orexin, norepinephrine, corticotropin-releasing factor, and cytokines. During the preoccupation/anticipation stage, individuals with AUD who are abstinent long-term present persistent sleep disturbances, including a longer latency to fall asleep, more time awake during the night, a decrease in slow-wave sleep, decreases in delta electroencephalogram power and evoked delta activity, and an increase in REM sleep. Glutamatergic system dysregulation that is observed in AUD is a likely substrate for some of these persistent sleep disturbances. Sleep pathology contributes to AUD pathology, and vice versa, possibly as a feed-forward drive to an unrecognized allostatic load that drives the addiction process.

Sleep Spindles: Mechanisms and Functions

Sleep spindles are burstlike signals in the electroencephalogram (EEG) of the sleeping mammalian brain and electrical surface correlates of neuronal oscillations in thalamus. As one of the most inheritable sleep EEG signatures, sleep spindles probably reflect the strength and malleability of thalamocortical circuits that underlie individual cognitive profiles. We review the characteristics, organization, regulation, and origins of sleep spindles and their implication in non-rapid-eye-movement sleep (NREMS) and its functions, focusing on human and rodent. Spatially, sleep spindle-related neuronal activity appears on scales ranging from small thalamic circuits to functional cortical areas, and generates a cortical state favoring intracortical plasticity while limiting cortical output. Temporally, sleep spindles are discrete events, part of a continuous power band, and elements grouped on an infraslow time scale over which NREMS alternates between continuity and fragility. We synthesize diverse and seemingly unlinked functions of sleep spindles for sleep architecture, sensory processing, synaptic plasticity, memory formation, and cognitive abilities into a unifying sleep spindle concept, according to which sleep spindles 1) generate neural conditions of large-scale functional connectivity and plasticity that outlast their appearance as discrete EEG events, 2) appear preferentially in thalamic circuits engaged in learning and attention-based experience during wakefulness, and 3) enable a selective reactivation and routing of wake-instated neuronal traces between brain areas such as hippocampus and cortex. Their fine spatiotemporal organization reflects NREMS as a physiological state coordinated over brain and body and may indicate, if not anticipate and ultimately differentiate, pathologies in sleep and neurodevelopmental, -degenerative, and -psychiatric conditions.

Using Oscillating Sounds to Manipulate Sleep Spindles

Introduction

EEG oscillations known as sleep spindles have been linked with various aspects of cognition, but the specific functions they signal remain controversial. Two types of EEG sleep spindles have been distinguished: slow spindles at 11-13.5 Hz and fast spindles at 13.5-16 Hz. Slow spindles exhibit a frontal scalp topography, whereas fast spindles exhibit a posterior scalp topography and have been preferentially linked with memory consolidation during sleep. To advance understanding beyond that provided from correlative studies of spindles, we aimed to develop a new method to systematically manipulate spindles.

Aims and Methods

We presented repeating bursts of oscillating white noise to people during a 90-min afternoon nap. During stage 2 and slow-wave sleep, oscillations were embedded within contiguous 10-s stimulation intervals, each comprising 2 s of white noise amplitude modulated at 12 Hz (targeting slow spindles), 15 Hz (targeting fast spindles), or 50 Hz followed by 8 s of constant white noise.

Results

During oscillating stimulation compared to constant stimulation, parietal EEG recordings showed more slow spindles in the 12-Hz condition, more fast spindles in the 15-Hz condition, and no change in the 50-Hz control condition. These effects were topographically selective, and were absent in frontopolar EEG recordings, where slow spindle density was highest. Spindles during stimulation were similar to spontaneous spindles in standard physiological features, including duration and scalp distribution.

Conclusions

These results define a new method to selectively and noninvasively manipulate spindles through acoustic resonance, while also providing new evidence for functional distinctions between the 2 types of EEG spindles.

Altered thalamocortical and intra-thalamic functional connectivity during light sleep compared with wake

The transition from wakefulness into sleep is accompanied by modified activity in the brain's thalamocortical network. Sleep-related decreases in thalamocortical functional connectivity (FC) have previously been reported, but the extent to which these changes differ between thalamocortical pathways, and patterns of intra-thalamic FC during sleep remain untested. To non-invasively investigate thalamocortical and intra-thalamic FC as a function of sleep stage we recorded simultaneous EEG-fMRI data in 13 healthy participants during their descent into light sleep. Visual scoring of EEG data permitted sleep staging. We derived a functional thalamic parcellation during wakefulness by computing seed-based FC, measured between thalamic voxels and a set of pre-defined cortical regions. Sleep differentially affected FC between these distinct thalamic subdivisions and their associated cortical projections, with significant increases in FC during sleep restricted to sensorimotor connections. In contrast, intra-thalamic FC, both within and between functional thalamic subdivisions, showed significant increases with advancement into sleep. This work demonstrates the complexity and state-specific nature of functional thalamic relationships--both with the cortex and internally--over the sleep/wake cycle, and further highlights the importance of a thalamocortical focus in the study of sleep mechanisms.

Alcohol and the sleeping brain

Alcohol acts as a sedative that interacts with several neurotransmitter systems important in the regulation of sleep. Acute administration of large amounts of alcohol prior to sleep leads to decreased sleep-onset latency and changes in sleep architecture early in the night, when blood alcohol levels are high, with subsequent disrupted, poor-quality sleep later in the night. Alcohol abuse and dependence are associated with chronic sleep disturbance, lower slow-wave sleep, and more rapid-eye-movement sleep than normal, that last long into periods of abstinence and may play a role in relapse. This chapter outlines the evidence for acute and chronic alcohol effects on sleep architecture and sleep electroencephalogram, evidence for tolerance with repeated administration, and possible underlying neurochemical mechanisms for alcohol's effects on sleep. Also discussed are sex differences as well as effects of alcohol on sleep homeostasis and circadian regulation. Evidence for the role of sleep disruption as a risk factor for developing alcohol dependence is discussed in the context of research conducted in adolescents. The utility of sleep-evoked potentials in the assessment of the effects of alcoholism on sleep and the brain and in abstinence-mediated recovery is also outlined. The chapter concludes with a series of questions that need to be answered to determine the role of sleep and sleep disturbance in the development and maintenance of problem drinking and the potential beneficial effects of the treatment of sleep disorders for maintenance of abstinence in alcoholism.

An intra-K-complex oscillation with independent and labile frequency and topography in NREM sleep

NREM sleep is characterized by K-complexes (KCs), over the negative phase of which we identified brief activity in the theta range. We recorded high resolution EEG of whole-night sleep from seven healthy volunteers and visually identified 2nd and 3rd stage NREM spontaneous KCs. We identified three major categories: (1) KCs without intra-KC-activity (iKCa), (2) KCs with non-oscillatory iKCa, and (3) KCs with oscillatory iKCa. The latter group of KCs with intra-KC-oscillation (iKCo), was clustered according to the duration of the iKCo. iKCa was observed in most KCs (1150/1522, 75%). iKCos with 2, 3, and 4 waves were observed in 52% (786/1522) of KCs in respective rates of 49% (386/786), 44%, and 7%. Successive waves of iKCos showed on average a shift of their maximal amplitude in the anterio-posterior axis, while the average amplitude of the slow KC showed no spatial shift in time. The iKCo spatial shift was accompanied by transient increases in instantaneous frequency from the theta band toward the alpha band, followed by decreases to upper theta. The study shows that the KC is most often concurrently accompanied by an independent brief iKCo exhibiting topographical relocation of amplitude maxima with every consecutive peak and transient increases in frequency. The iKCo features are potentially reflecting arousing processes taking place during the KC.

Concomitant BDNF and sleep slow wave changes indicate ketamine-induced plasticity in major depressive disorder

The N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has rapid antidepressant effects in treatment-resistant major depressive disorder (MDD). In rats, ketamine selectively increased electroencephalogram (EEG) slow wave activity (SWA) during non-rapid eye movement (REM) sleep and altered central brain-derived neurotrophic factor (BDNF) expression. Taken together, these findings suggest that higher SWA and BDNF levels may respectively represent electrophysiological and molecular correlates of mood improvement following ketamine treatment. This study investigated the acute effects of a single ketamine infusion on depressive symptoms, EEG SWA, individual slow wave parameters (surrogate markers of central synaptic plasticity) and plasma BDNF (a peripheral marker of plasticity) in 30 patients with treatment-resistant MDD. Montgomery-Åsberg Depression Rating Scale scores rapidly decreased following ketamine. Compared to baseline, BDNF levels and early sleep SWA (during the first non-REM episode) increased after ketamine. The occurrence of high amplitude waves increased during early sleep, accompanied by an increase in slow wave slope, consistent with increased synaptic strength. Changes in BDNF levels were proportional to changes in EEG parameters. Intriguingly, this link was present only in patients who responded to ketamine treatment, suggesting that enhanced synaptic plasticity - as reflected by increased SWA, individual slow wave parameters and plasma BDNF - is part of the physiological mechanism underlying the rapid antidepressant effects of NMDA antagonists. Further studies are required to confirm the link found here between behavioural and synaptic changes, as well as to test the reliability of these central and peripheral biomarkers of rapid antidepressant response.

Spindle power is not affected after spontaneous K-complexes during human NREM sleep

K-complexes and sleep spindles often grouped together characterize the second stage of NREM sleep and interest has been raised on a possible interaction of their underlying mechanisms. The reported inhibition of spindles power for about 15 seconds following evoked K-complexes has implications on their role in arousal. Our objective was to assess this inhibition following spontaneous K-complexes. We used time-frequency analysis of spontaneous K-complexes selected from whole-night EEG recordings of normal subjects. Our results show that spindles are most often observed at the positive phase following the peak of a spontaneous KC (70%). At latencies of 1-3 s following the peak of the K-complex, spindles almost disappear. Compared to long-term effects described for evoked KCs, sleep spindle power is not affected by spontaneous KCs for latencies of 5-15 s. Observation of the recurrence rate of sporadic spindles suggests that the reduction of power at 1-3 s most likely reflects a refractory period of spindles lasting for 1-2 s, rather than an effect of KCs. These results suggest that the mechanisms underlying spontaneous KCs do not affect spindle power as in the case of evoked KCs.

Large-scale functional brain networks in human non-rapid eye movement sleep: insights from combined electroencephalographic/functional magnetic resonance imaging studies

This paper reviews the existing body of knowledge on the neural correlates of spontaneous oscillations, functional connectivity and brain plasticity in human non-rapid eye movement (NREM) sleep. The first section reviews the evidence that specific sleep events as slow waves and spindles are associated with transient increases in regional brain activity. The second section describes the changes in functional connectivity during NREM sleep, with a particular focus on changes within a low-frequency, large-scale functional brain network. The third section will discuss the possibility that spontaneous oscillations and differential functional connectivity are related to brain plasticity and systems consolidation, with a particular focus on motor skill acquisition. Implications for the mode of information processing per sleep stage and future experimental studies are discussed.

Development of a large-scale functional brain network during human non-rapid eye movement sleep

Graph theoretical analysis of functional magnetic resonance imaging (fMRI) time series has revealed a small-world organization of slow-frequency blood oxygen level-dependent (BOLD) signal fluctuations during wakeful resting. In this study, we used graph theoretical measures to explore how physiological changes during sleep are reflected in functional connectivity and small-world network properties of a large-scale, low-frequency functional brain network. Twenty-five young and healthy participants fell asleep during a 26.7 min fMRI scan with simultaneous polysomnography. A maximum overlap discrete wavelet transformation was applied to fMRI time series extracted from 90 cortical and subcortical regions in normalized space after residualization of the raw signal against unspecific sources of signal fluctuations; functional connectivity analysis focused on the slow-frequency BOLD signal fluctuations between 0.03 and 0.06 Hz. We observed that in the transition from wakefulness to light sleep, thalamocortical connectivity was sharply reduced, whereas corticocortical connectivity increased; corticocortical connectivity subsequently broke down in slow-wave sleep. Local clustering values were closest to random values in light sleep, whereas slow-wave sleep was characterized by the highest clustering ratio (gamma). Our findings support the hypothesis that changes in consciousness in the descent to sleep are subserved by reduced thalamocortical connectivity at sleep onset and a breakdown of general connectivity in slow-wave sleep, with both processes limiting the capacity of the brain to integrate information across functional modules.

K-complex, a reactive EEG graphoelement of NREM sleep: an old chap in a new garment

This review summarises data gathered on the KC phenomenon over the past 70 yr. The following issues are discussed: definitions, morphology and topography of KC, the regular participation in NREM sleep, elicitability features of evoked KC, autonomic and motor concomitants, relationship of KC with information processing during NREM sleep, relationship of KC and deltas of NREM sleep, and relationship of KC with sleep cyclicity. KC is a complex multifunctional phenomenon of the sleeping brain involved in information processing and defence against the arousal effect of sensory stimuli. To put the old chap in a new garment, the relationship of KC with synchronisation-type and desynchronisation-type micro-arousals, and the 'cyclic alternating pattern', will be discussed, with an emphasis on the sleep-protecting role of KC and synchronisation-type answers in sleep regulation executed by phasic events. Lastly, the role of KC providing gating functions in idiopathic generalized epilepsies and other, different, sleep disorders are characterised. A 'theoretical epilogue' is appended to show some system theoretical and regulational aspects.

Regional differences in the circadian modulation of human sleep spindle characteristics

Electroencephalographic oscillations in the sleep spindle frequency range (11-16 Hz) are a key element of human nonrapid eye movement sleep. In the present study, sleep spindle characteristics along the anterior-posterior axis were analysed during and outside the circadian phase of melatonin secretion. Sleep electroencephalograms were recorded during naps distributed over the entire circadian cycle and analysed with two different methodological approaches, the classical fast Fourier transform in the frequency-domain and a new method for instantaneous spectral analysis, the fast time frequency transform that yields high-resolution parameters in the combined time-frequency-domain. During the phase of melatonin secretion, spindle density was generally increased and intraspindle frequency variation reduced. Furthermore, lower spindle frequencies were promoted: peak frequencies shifted towards the lower end of the spindle frequency range, and spindle amplitude was enhanced in the low-frequency range (11-14.25 Hz) and reduced in the high-frequency range (approximately 14.5-16 Hz). The circadian variation showed a clear dependence on brain topography such that it was maximal in the parietal and minimal in the frontal derivation. Our data provide evidence that the circadian pacemaker actively promotes low-frequency sleep spindles during the biological night with a parietal predominance.

Diazepam-induced changes on sleep and the EEG spectrum in mice: role of the alpha3-GABA(A) receptor subtype

Benzodiazepines reduce EEG slow-wave activity in non-REM sleep by potentiating GABAergic neurotransmission at GABAA receptors via a modulatory binding site. However, the mechanisms of action underlying the effects of benzodiazepines on sleep and the sleep EEG are still unknown. Slow waves during sleep are generated by the corticothalamic system and synchronized by the inhibitory GABAergic neurons of the reticular thalamic nucleus. This region contains exclusively alpha3-containing GABAA receptors. We investigated the role of these receptors in the mediation of diazepam effects on the sleep EEG by studying point-mutated mice in which the alpha3-GABAA receptor is diazepam-insensitive [alpha3(H126R)]. Sleep was recorded for 12 h after i.p. injection of 3 mg/kg diazepam or vehicle at light onset in alpha3(H126R) and wild-type controls (n = 13-17 per genotype). The main effect was a marked reduction of slow-wave activity (EEG power density in 0.75-4.00 Hz) in non-REM sleep and a concomitant increase in frequencies above 15.00 Hz in non-REM sleep and waking in both genotypes. Neither effect of diazepam differed significantly between the genotypes. Despite the exclusive expression of alpha3-containing GABAA receptors in the reticular thalamic nucleus, these receptors do not seem to be critical for the mediation of the effects of diazepam on the sleep EEG.

Sleep spindles in human prefrontal cortex: an electrocorticographic study

To investigate the sleep spindle activity of the human prefrontal cortex (PFC), we simultaneously recorded whole nights of polysomnographic and electrocorticographic (ECoG) activities during the natural sleep of epileptic patients. Subjects were nine patients with intractable epilepsy who had subdural electrodes surgically attached to the orbital (seven cases), medial (three cases), or dorsolateral (two cases) PFC, and in one case to the frontal pole. To examine spindle frequencies, fast Fourier transformation (FFT) and auto-correlation analyses were performed on the PFC ECoG and Cz EEG data, primarily on epochs of stage 2 sleep. Lower sigma band ECoG oscillations of about 12 Hz were widely distributed across all prefrontal cortical areas including the frontal limbic regions, but none of the PFC sigma frequency peaks coincided with the faster (about 14 Hz) Cz EEG sleep spindles. Combining our results with anatomical and electrophysiological facts, it is suggested that the thalamofrontal circuit involving the rostral reticular and the mediodorsal nucleus of the thalamus is responsible for the generation of 12 Hz frontal spindles in humans.

Probing awareness during sleep with the auditory odd-ball paradigm

During the waking state, a late component of the auditory event-related potential, P300, is elicited when subjects detect a rare 'target' stimulus. It is usually not elicited when subjects either ignore or fail to detect the stimulus. The presence of P300 is therefore thought to reflect conscious processing of the stimulus. Since P300 has been shown to be an attention-dependent cognitive component in wakefulness, one might suppose that it would be absent during sleep-a time in which information processing of external stimuli is commonly thought to be inhibited. This review examines the presence or absence of P300 in studies employing auditory odd-ball paradigms in sleep. Research to date indicates that P300 can be recorded during the transition to sleep and then reappears in REM sleep. Stimuli that are rare and intrusive are more likely to elicit the classic parietal P300 in REM sleep. There is, however, little or no positivity at frontal sites. This is consistent with brain imaging studies that show frontal deactivation is characteristic of REM sleep. These findings indicate that while sleepers may be able to detect stimulus deviance in stage 1 and REM, the frontal contribution to consciousness may be lost. In non-REM sleep, a later positive wave at 450 ms does not vary according to experimental manipulation in the same way as the waking and REM P300s. This non-REM sleep-related positivity may therefore underlie mechanism distinct from the waking P300.

Spindle activity in children during cardiac surgery and hypothermic cardiopulmonary bypass

Hypothermia has marked effects on the electrical activity of the brain, which has been shown in animals as well as in humans. The aim of this study was to investigate EEG spindle activity in children during cardiac surgery and hypothermic cardiopulmonary bypass. The authors obtained intraoperative 21-channel EEG recordings in 36 children (mean age, 22 months; range, 6 days to 69 months) with congenital heart disease. Bipolar EEG derivations were analyzed visually for rhythmic spindle activity based on morphology, frequency, duration, and amplitude. Linear regression analysis for duration, frequency, and amplitude versus rectal temperature was performed in each individual. Spindle activity was observed in 17 children (16 children < 12 months of age). Progressive slowing of spindle frequency with decreasing rectal temperature was found (mean decrease, 0.54 +/- 0.31 Hz/ degrees C). Spindle duration increased on average by 0.69 +/- 0.39 second/ degrees C during cooling procedures. Spindle amplitude did not show any correlation to changes in rectal temperature. The current study demonstrates spindle activity during hypothermic cardiopulmonary bypass with temperature-dependent spindle modifications of frequency and duration. Although the temperature-dependent changes in this study confirm temperature coefficients of other EEG studies, the reasons for the clear age relationship and the "nature" of these spindles remain unknown.

Temporo-spatial correlations between scalp and centromedian thalamic EEG activities of stage II slow wave sleep in patients with generalized seizures of the cryptogenic Lennox-Gastaut syndrome

OBJECTIVES

Temporo-spatial correlations between scalp and centromedian thalamic (CM) normal and abnormal electroencephalographic (EEG) activities of stage II slow wave sleep (SWS II) were investigated in 5 patients with cryptogenic Lennox-Gastaut syndrome (CLGS).

METHODS

In each patient, 8h/all-night sleep studies were performed with routine methods; and a total of 1233 normal and 206 abnormal individual activities, spontaneously occurring during 200 epochs of early and late SWS II, were analyzed. Normal activities included scalp-CM K-complexes (KC-CMKC), vertex waves (VW-CMVW), and sleep spindles (SS-CMSS). Abnormal activities included: thalamo-cortical spikes (TCS-CMTCS), and epileptic (EPKC-CMEPKC) and W K-complexes (WKC-CMWKC).

RESULTS

(1) All abnormal and normal spontaneous SWS II activities occurred associated in scalp and CM regions except the SS. Associated spindles were significantly larger (P<0.01) than dissociated ones, this occurring during both early and late SWS II. (2) The peak of VW significantly anticipated (P<0.02) that of its CM counterpart (CM-VW), while the peak of CMTCS anticipated that of its scalp counterpart. The onset of CMSS significantly anticipated (P=0.02) that of its scalp counterpart (SS). The behavior of VW-CMVW and TCS-CMTCS of the abnormal KC was similar to those of the normal complexes, while the onset of abnormal spindles was simultaneous in scalp and CM regions. Scalp VW, CTS, and SS attained maximal amplitude at the parietal region bilaterally with decreasing amplitude gradients to other scalp regions, while CMVW, CMTCS, and CMSS attained maximal amplitude in all thalamo-mesencephalic regions of CM. (3) Normal spindles significantly reduced (P<0.02) the amplitude of the positive CM, CMVW, and scalp TCS counterparts of the negative scalp VW and CM (CMTCS), respectively, while abnormal spindles reduced the amplitudes (P<0.01) of both negative VW and CMTCS and positive counterparts.

CONCLUSION

These data suggest the following: (1) that all SWS II activities, including SS, are mediated by common thalamo-cortical systems; (2) that VW originate from the parietal scalp and normal spindles and TCS from the CM regions bilaterally while abnormal spindles originate either from widespread cortical and CM regions or from a site outside the thalamo-cortical systems, and (3) that the functional role of SS is to inhibit non-specific thalamo-cortical systems for sleep preservation.

Effects of hypnotics on the sleep EEG of healthy young adults: new data and psychopharmacologic implications

Benzodiazepine hypnotics increase NREM sleep and alter its EEG by reducing delta (0.3-3 Hz) and increasing sigma (12-15 Hz) and beta (15-23 Hz) activity. We tested whether the nonbenzodiazepine hypnotic, zolpidem (10 mg), produced the same pattern of sleep and EEG changes as two "classical" benzodiazepines, triazolam (0.25 mg) and temazepam (30 mg). Sleep EEG of 16 subjects was analyzed with period amplitude analysis for 3 nights during drug administration or placebo. The effects of zolpidem were in the same direction but generally of smaller magnitude than those of the classical benzodiazepines. These differences are more likely the result of non-equivalent dosages than different pharmacologic actions. Period amplitude analysis showed that the decreased delta activity resulted mainly from a decrease in wave amplitude. In contrast, the increased sigma and beta activity were produced by increased wave incidence. Delta suppression increased with repeated drug administration but sigma and beta stimulation did not. While these findings have little relevance for the clinical choice of hypnotics they may hold important implications for the brain mechanisms involved in hypnotic tolerance and withdrawal delirium.

EEG arousals and awakenings in relation with periodic leg movements during sleep

It is known that periodic leg movements are frequently accompanied by full awakenings or by signs of EEG arousals. The time relationship of these EEG arousals with leg movements varies from patient to patient. They may precede or follow leg movements or occur simultaneously. It is not clear whether these arousals trigger leg movements or, alternatively, whether both EEG arousals and leg movements are separate expressions of a common pathophysiological mechanism. We investigated the temporal relationship of five EEG arousals, such as alpha activity, K-complexes, spindles, K-alpha, K-spindle activities and awakenings, with leg movements in 10 periodic leg movement patients. These EEG arousals were considered to be associated with leg movements if they occurred 10 s before/after or simultaneously with the onset of right or left tibialis muscle EMG potentials. It was found that 49.19% of EEG arousals occurred before leg movements, 30.61% occurred simultaneously and 23.18% occurred just after leg movements. The number of EEG arousals was significantly higher in the 10 s preceding leg movement than simultaneously or in the 10 s following. Alpha activity was the phenomenon associated most frequently with leg movements, irrespective of its temporal organization and was significantly higher during the 10 s preceding movement. Spindle and K-spindle activities were significantly higher before leg movement, whereas K-complex activity was significantly more frequent during leg movements. The number of awakenings was significantly higher after leg movements than simultaneously. These results indicated that leg movements are not primary, but rather are a phenomenon associated with an underlying arousal disorder.

Independence of sleep EEG responses to GABAergic hypnotics: biological implications

GABAergic hypnotics are known to depress non-rapid eye movement delta and rapid eye movements and to stimulate non-rapid eye movement sigma (spindles) and beta EEG. This study addressed the question of whether the magnitudes of these effects are significantly correlated. Data were from a study in 16 normal subjects whose sleep was recorded for five nights under placebo and for three nights each under zolpidem (10 mg), triazolam (0.25 mg) and temazepam (30 mg). EEG was analyzed with both period-amplitude and power spectral (FFT) analysis. The magnitudes of the EEG and eye movement density responses were not significantly correlated for any of the three drugs. It is therefore unlikely that sleep responses to GABAergic drugs can be explained by the common cellular action (increased chloride conductance) of these drugs. We suggest that the sleep EEG responses are manifestations of complex (but consistent) interactions of excitation and inhibition in large brain systems although certain aspects of these responses (e.g. the different time courses of delta vs sigma and eye movement responses) may reflect molecular adaptations. A separate observation in this study was the strong traitlike characteristics of the sleep variables studied. These variables were highly correlated across nights of baseline sleep; in addition, individual differences in baseline sleep were significantly retained on the third night of temazepam administration.

Hierarchy of micro-arousals and the microstructure of sleep

This review is aimed at providing an overview concerning the hierarchy of different kinds of micro-arousals (without awakening) during slow wave sleep (SWS), and to summarize available data on the dynamic interplay of phasic events constituting the microstructural web of sleep EEG. K-complexes are considered elementary forms of arousal during SWS. They carry characteristics of evoked potentials, which provide subattentive information processing and have at the same time level-setting sleep maintenance functions. Micro-arousals are more complex arousal-dependent phasic events in the hierarchy. One class of recurring micro-arousals are preceded by K-complexes, while others, such as phases of spontaneous transitory activation--type micro-arousals-- represent higher levels of arousal, and are associated with EEG desyncronization, increased muscle activity and signs of autonomous arousal. All types of micro-arousals function in a complex interrelationship with another phasic event--sleep spindles--interpreted as microstates inhibiting sensory inflow through the thalamic relay system. Lastly the CAP (cyclic alternating pattern) phenomenon offers a global framework for characterizing and measuring arousal instability. Appearance of CAP sequences reflects arousal instability in a higher duration range than individual micro-arousals. They represent an arousal control mechanism reflecting that all arousing influences set into motion an oscillatory level setting system around the referential state providing a flexible adaptation for the system to defend it against perturbations. The whole arousal (without awakening) hierarchy thus seems to play an essential role in sleep regulation, serving both cyclicity and maintenance of sleep and providing at the same time flexible contact between sleeper and environment--preserving the possibility to wake up in case of any biological danger, and tailoring sleep program according to actual environmental or inner demands. Although at present there are no accepted rules for microstructural evaluation of sleep, microstructural aspects provide a more dynamic picture both about the preprogrammed and reactive changes in sleep. This approach gives us some clues to better understand sleep disorders as well. Several studies concerning microstructural analysis of certain sleep disorders are also reviewed.

Effect of the GABA uptake inhibitor tiagabine on sleep and EEG power spectra in the rat

1. The sleep profiles induced by agonists and agonistic modulators of gamma-aminobutyric acidA (GABA[A]) receptors differ markedly. With regard to GABA(A) agonists, the effects may be due to the fact that these agents are poor substrates for uptake and are therefore likely to activate GABA(A) receptors tonically. To investigate this possibility, we assessed the sleep effects of two doses (2 and 10 mg kg[-1]) of the GABA re-uptake inhibitor tiagabine, administered intraperitoneally at light onset in 8 rats. Electroencephalogram (EEG) and electromyogram were recorded during the first 8 h after the injection. 2. Compared with vehicle, tiagabine had minimal effects on the temporal pattern of non-rapid eye movement sleep (non-REMS) and on the total time spent therein. However, tiagabine dose-dependently elevated EEG activity during non-REMs, most prominently in the lower frequencies (1-8 Hz) and least pronounced in the frequencies between 11 and 16 Hz. During the first 2 h after the injection, 10 mg kg(-1) tiagabine elicited repetitive episodes of hypersynchronous EEG waves during wakefulness and slightly suppressed REMS. Except for these effects, tiagabine hardly influenced the time spent in and EEG activity during wakefulness and REMS. 3. The effects of tiagabine on state-specific EEG activity were qualitatively very similar to those elicited by GABA(A) agonists. These findings support the hypothesis that the influence of GABA(A) agonists on EEG signals may be caused by tonic stimulation of GABA(A) receptors.

The intermediate stage and paradoxical sleep in the rat: influence of three generations of hypnotics

Paradoxical sleep in the rat, cat and mouse is preceded and sometimes followed by a short-lasting intermediate stage characterized by high-amplitude anterior cortex spindles and low-frequency hippocampal theta rhythm. Several neurophysiological arguments suggest that the intermediate stage corresponds to a brief functional disconnection of the forebrain from the brainstem. This paper is devoted to the review of quantitative and qualitative influences of three generations of hypnotics on the intermediate stage-paradoxical sleep couple. Barbiturates, first-generation hypnotics, extend the intermediate stage at the expense of paradoxical sleep. Three benzodiazepines are compared, two with a short half-life (triazolam and midazolam) and one with a long half-life (diazepam). They also decrease sleep occurrence latency and increase the intermediate stage at the expense of paradoxical sleep, except for midazolam, which increases both the intermediate stage and paradoxical sleep at low dose. Zolpidem and zopiclone, hypnotics of third generation, decrease paradoxical sleep but the intermediate stage never substitutes for paradoxical sleep. The results are discussed in relationship to the functional aspects of this turning-point period of sleep.

Muscimol and midazolam do not potentiate each other's effects on sleep EEG in the rat

The interaction of a gamma-aminobutyric acid-A (GABAA) receptor agonist and a benzodiazepine-type modulator of GABAA receptors on sleep was investigated. Low doses of muscimol (0.3 mg/kg) and the benzodiazepine midazolam (1.5 mg/kg) were administered alone and in combination, in random order, to eight rats. All injections were given intraperitoneally at light onset. Electroencephalogram (EEG) and electromyogram were recorded during the first 6 h post injection. Compared with vehicle, muscimol hardly affected the time spent in non-rapid eye movement sleep (non-REMS) and REMS, but significantly enhanced EEG activity in the frequency range between 2 and 6 Hz during non-REMS. Midazolam significantly increased the time spent in non-REMS, reduced EEG activity at frequencies < 12 Hz, and elevated EEG activity in most higher frequencies during this state. The combined administration of muscimol and midazolam affected non-REMS-specific EEG activity in an unexpected fashion: the effects were intermediate between those of muscimol and midazolam. These results indicate that muscimol and midazolam have dissimilar effects on EEG within non-REMS and demonstrate that midazolam does not augment but attenuates the muscimol-induced changes in sleep EEG. Our data are at variance with established mechanisms, according to which agonistic modulators would have similar effects and should potentiate the effects of GABAA agonists. The present data suggest that application of agonists and agonistic modulators of GABAA receptors causes differential net effects on sleep parameters.

Dynamics of EEG spindle frequency activity during extended sleep in humans: relationship to slow-wave activity and time of day

The dynamics of EEG spindle frequency activity (SFA; spectral power density in the 12.25-15.0 Hz range) and its relationship to slow-wave activity (SWA; 0.75-4.5 Hz) were investigated in long sleep episodes (> 12 h). Young healthy men went to bed at either 19:00 h (early sleep; prior waking 36 h, n = 9) or 24:00 h (late sleep; prior waking 17 h, n = 8). In both nights, SWA in non-rapid-eye-movement sleep (NREMS) decreased over the first three to four 1.5-h intervals and remained at a low level in the subsequent five to six 1.5-h intervals. In contrast, the changes of SFA were more variable and differed between the lower (12.25-13.0 Hz), middle (13.25-14.0 Hz) and higher frequency bin (14.25-15.0 Hz). A pronounced influence of time of day was present in the lower and higher SFA bin, when the dynamics were analyzed with respect to clock time. In both the early and late sleep condition, power density in the lower bin was highest between 2:00 and 5:00 h in the morning and decreased thereafter. In the higher bin, power density was low in the early morning hours and increased as sleep was extended into the daytime hours. The results provide further evidence for a frequency-specific circadian modulation of SFA which becomes more evident at a time when SWA is low.

Changes in sleep spindle activity of subject with chronic somatosensitive and sensorial deficits. Preliminary results

We investigated the effects of the somatosensitive and sensory afferent inputs on the thalamic generators of sleep spindles (SS) in adult subjects affected by posterior funiculi lesions (five subjects), deafness (four subjects) or blindness (four subjects). The density, duration and frequency of SS, as well as the index of spindling, were analyzed during stage 2 NREM. The results show that the subjects with somatosensitive and sensorial lesions spent much more time on SS activity than the control group (eight subjects), and had a significantly increased density (< .0001), duration (< .0005) and index of spindling (< .0001). On the other hand, the frequency of spindling was little modified (< .05). Moreover, among the three groups of patients, those with somatosensitive deficits showed the greatest SS activity. In conclusion, our results suggest that the thalamic generators of SS are markedly modulated by peripheral inputs in man.

Flunitrazepam effects on human sleep EEG spectra: Differences in NREM, REM and individual responses

Flunitrazepam (FNZ) (4mg), an intermediate type benzodiazepine (BDZ) hypnotic, was administered orally to five healthy male subjects (Ss) for seven consecutive nights. Sleep EEG from the baseline night (BLN), the initial drug night (IDN), the fourth and the seventh drug nights (4DN, 7DN) was subjected to fast Fourier transform (FFT) analysis. During NREM sleep of 4DN and 7DN the sigma band (11.0-12.5 Hz) activity was similarly enhanced in every S. In REM of 4DN and 7DN beta band (23.0-29.0 Hz) was enhanced, but with larger variations among Ss. High intra-individual consistency of the relative EEG power patterns on 4DN and 7DN was observed. These results suggest that 1) EEG responses to FNZ are different in sleep states; explorations of these differences may provide better understandings of sleep mechanisms, and 2) individual variations in EEG responses may reflect individual variations of the BDZ receptor system. These methods may be useful for exploring receptor changes in neuropsychiatric disorders.

Melatonin effect on daytime sleep in men: suppression of EEG low frequency activity and enhancement of spindle frequency activity

The effect of melatonin (5 mg, p.o.) on electroencephalographic (EEG) activity during sleep was investigated in eight men in a placebo-controlled cross-over design. Melatonin was administered immediately prior to a 4-h daytime sleep episode (13-17 h) after a partial sleep deprivation. The non-REM sleep stages and REM sleep duration were not significantly affected. Melatonin enhanced EEG power density in non-REM sleep in the 13.75-14.0 Hz bin (i.e., within the frequency range of sleep spindles), and reduced activity in the 15.25-16.5 Hz band. In the first 2 h spectral values within the 2.25-5.0 Hz range were reduced. These changes in the EEG are to some extent similar to those induced by benzodiazepine hypnotics and to the contribution of the endogenous circadian pacemaker to the spectral composition of the sleep EEG when sleep occurs at night.

Quantitative description of EEG periodicities during stationary sleep stages

A quantitative method was applied in order to assess variations in EEG activities during sleep. Three classes of variations were distinguished: variations connected with sleep-stage changes (class 1), higher-frequency variations described by the envelope of frequency-band activities (class 2), intermediate-frequency variations, corresponding to periods from 4 to 120 s (class 3). For each class, parameters characterizing the frequency spectra were computed. These parameters were mathematically simple and clear in their meaning, since they measured power, modulation index and mean squared frequency. A statistical comparison of the mean values of the parameters during different sleep stages evidenced a certain number of significant shifts in each of the three classes. The most important class-1 and class-2 variations were described by our parameters with high levels of significance. The results obtained for class 3 were in agreement with visual observations reported in the literature, such as the progressive increase in the interval between successive arousals from sleep onset to Stage 4 and the frequent occurrence of cyclic alternating patterns during Stage 2 epochs immediately preceding REM sleep.

Sleep in a sitting position: effect of triazolam on sleep stages and EEG power spectra

The effect of triazolam (0.25 mg) and placebo was investigated in healthy, male subjects who slept in a sitting position. After the intake of placebo, sleep efficiency, rapid eye movement (REM) sleep and subjective sleep quality were lower than in the preceding sleep episode in bed, while stage 1 and REM sleep latency were higher. Triazolam did not prevent this impairment of sleep. However, in comparison with the placebo condition, the percentage of slow wave sleep was higher in the first third of the night, and in the morning sleep was rated as more quite. EEG power density in nonREM sleep was reduced in the frequency range of 1.25-10.0 Hz and enhanced in the range of sleep spindles (12.25-13.0 Hz). These changes were still present in the last third of the night. In REM sleep, triazolam reduced spectral activity in some frequency bins between 4.25 and 10.0 Hz. The sitting position itself affected the nonREM sleep spectra, since the placebo level in the 2.25-21.0-Hz range exceeded the baseline level. We conclude that a 0.25 mg dose of triazolam does not effectively counteract a posture-induced sleep disturbance, but induces changes in the EEG spectra which are typical for benzodiazepine receptor agonists.

Dynamic relationships between sleep spindles and delta waves during a NREM period

All-night sleep EEGs from 7 normal young male adults were analyzed by a waveform recognition method using FFT-IFFT band pass filters. The total durations of sleep spindles and sleep delta waves in each 20-s epoch were measured and plotted on an X-Y graph with lines connecting the points in time sequence (dynamic two-component plot). The relationship between these two measures within a single NREM period showed three dynamic phases and one stationary period. In the first phase, spindles increased while delta remained at low level or increased slightly. In the second phase delta increased greatly while spindles decreased. In the third phase, delta decreased while spindles remained at a low level. There was a stationary period between the second and third phases, when delta maintained a higher level and spindles maintained a lower level. These dynamic descriptions reflect the underlying physiological mechanisms more directly than static sleep stages. They should also permit finer analyses of sleep in psychiatric and neurological disorders.

Effects of zopiclone on slow wave sleep and spontaneous K-complexes for normal healthy young adults

Benzodiazepine (BZD) hypnotics have been known to decrease, to some degree, human slow wave sleep (SWS) although they elevate the arousal threshold during sleep. Zopiclone (ZPC), a cyclopyrrolone hypnotic, has attracted the interest of sleep researchers because an increase in human SWS has been reported. Since the increase has not been fully confirmed by all of the studies, the authors investigated the effects of ZPC 10 mg on SWS and the K-complexes for 7 healthy young adults because there is evidence indicating that delta waves consisting of SWS and the spontaneous K-complexes are identical. SWS and st. 4 sleep did not decrease on any of the ZPC nights but st. 3 sleep showed a tendency to reduce on the 1st ZPC night. The frequency of the K-complexes decreased significantly on the 2nd ZPC night and tended to reduce on the 1st ZPC night. Moreover, a significant positive correlation was noted between the decrease rates of SWS and the K-complexes on both the ZPC nights. The authors, therefore, could not obtain any findings suggesting an increase in SWS with ZPC.

Arousals without awakening--dynamic aspect of sleep

K complex as an elementary form of arousal was investigated by evoked K complexes. The components building up evoked K complexes and topographical sleep-level differences and influence of the kind of cognitive elaboration were analysed. Evidences are presented supporting that K complex represents a cascade of events originating from sources of different topography and probably by a different kind of elaboration activated in a certain order requested by the nature and context of the eliciting stimuli. The power spectra of evoked arousals--including K complexes--were investigated. The poststimulus spectral pattern is characterized by a short initial power elevation and a following reduction of all frequency bands except a simultaneous but prolonged (5-20 s) and strong (50%) power reduction at the 13-14 Hz sigma spindle band. This phenomenon seems to be a common feature in different stages of slow wave sleep. This stimulus-related microstate could serve as a transitory stand-by state ready to reach higher arousal rapidly while maintaining the continuity of sleep; hence, the inhibition of spindle activity could provide a phasically improved thalamocortical sensory inflow after environmental stimuli. A microstructural scheme of arousals without awakening has been delineated.

Improved procedure of complex demodulation and an application to frequency analysis of sleep spindles in EEG

Complex demodulation is a local version of harmonic analysis that enables the amplitude and phase of particular frequency components of a time series to be described as functions of time. The paper presents a computational procedure involving complex demodulation with interpolation of data in the frequency domain. A computational procedure comprising repeated use of complex demodulation is also presented. This is used to estimate the optimum choice of the demodulating frequency which considerably influences the measurement of the instantaneous amplitude and phase of the underlying process. The usefulness of this procedure is verified by computer simulation. An example of applying this procedure to the estimation of the centre and the instantaneous frequencies of sleep spindles in the EEG (electroencephalogram) is presented. By using the procedure developed here, several partially overlapping sleep spindles are detected and correctly separated. The paper also presents an approach to separating and analysing transient time series (such as overlapping sleep spindles) by using an accurate frequency processing technique.

Effects of generalized interictal EEG discharges on sleep stability: assessment by means of cyclic alternating pattern

Generalized interictal EEG discharges are influenced by a biphasic (phase A and B) modality of arousal control during non-rapid eye movement (REM) sleep termed cyclic alternating pattern (CAP). Each phase A and the following phase B compose a CAP cycle. The percentage ratio of total CAP time to total non-REM sleep time is the CAP rate, a sleep parameter that measures the instability and fragmentation of sleep. Since CAP exerts a powerful influence on generalized interictal EEG discharges during sleep, the polysomnograms of seven epileptic patients affected by a clinically active form of primary generalized epilepsy were matched with those of seven healthy volunteers of the same age and sex to assess the influence of interictal discharges on sleep organization. No remarkable differences emerged when the traditional polysomnographic parameters were compared between the two groups. However, the epileptic patients showed significantly higher CAP rate values (52.7 vs. 34.6%; p less than 0.003), indicating a greater arousal instability in the sleep records of these subjects. Within the epileptic group, the CAP cycles that included at least one interictal paroxysm were significantly longer than those without EEG discharges (31.2 vs. 25.4 s; p less than 0.007). The selective lengthening of CAP cycles is likely due to an exaggeration of the natural activating power of phase A when coupled with EEG paroxysms and an intensification of the inhibitory properties of the following phase B. The dynamic relationships and differences between spindles in animals, k-complexes, and slow-wave bursts in humans may have a functional linkage with epileptic phenomena during sleep.

Sleep spindles in epilepsy

Spindles are a ubiquitous phenomenon in sleep, but their physiology and the effects of neurologic disorder on their frequency and amplitude are incompletely understood. We compared the incidence of three commonly defined spindle types (14-15 Hz, 12-13 Hz, and 10 Hz) and the frequency and amplitude of spindles during Stage II sleep in 50 patients with complex partial, partial and secondarily generalized, and primary generalized seizures, with and without interictal behavioral symptoms. All patients had 12-13 Hz and 14-15 Hz spindles of symmetric character in C3-A1 and C4-A2 derivations during prolonged sleep-deprived EEG recordings, which were normal except for partial or generalized epileptiform activity. Seventy-one per cent of complex partial seizure patients had 10 Hz spindles, and they occurred in 50% of the other two groups, predominating among those with interictal behavioral symptoms in all groups. Spindle frequency was significantly less in patients with generalized epilepsy than with partial seizures, and patients with complex partial seizures and partial seizures with secondary generalization differed significantly in spindle frequency. Spindle frequency was significantly lower with polypharmacy than with monotherapy. Patients whose regimens included phenobarbital had significantly lower spindle frequencies and spindle frequencies differed significantly between phenytoin and carbamazepine. Differences in spindle frequency may be due to residual medication effects, underlying encephalopathy or physiological differences between partial and generalized epilepsy.

Sigma (12-15 Hz) and delta (0.3-3 Hz) EEG oscillate reciprocally within NREM sleep

Sleep EEG in the sigma and delta frequency bands was subjected to spectral analysis in 8 normal young adults. In each subject, power density of sigma and delta oscillated reciprocally during NREM sleep, confirming an observation made initially with period/amplitude analysis. In REM sleep, power density for both frequency bands was at its lowest levels. Correlation coefficients between power density of delta vs. 1/sigma for all artifact-free 20-s epochs of NREM sleep/night were highly significant for each subject. These results show that cyclic oscillation of EEG within sleep is not limited to delta frequencies. The reciprocal relation of sigma to delta holds implications for the EEG mechanisms of NREM sleep. This dynamic pattern may also prove useful for sleep stage scoring and for a finer empirical analysis of sleep in psychiatric and neurological disorders.