Vertex Sharp Waves Research Articles

Admission Clinical and EEG Features Associated With Mortality and Long-term Neurologic and Cognitive Outcomes in Pediatric Cerebral Malaria.

For children with cerebral malaria, mortality is high, and in survivors, long-term neurologic and cognitive dysfunctions are common. While specific clinical factors are associated with death or long-term neurocognitive morbidity in cerebral malaria, the association of EEG features with these outcomes, particularly neurocognitive outcomes, is less well characterized. In this prospective cohort study of 149 children age 6 months to 12 years who survived cerebral malaria in Kampala, Uganda, we evaluated whether depth of coma, number of clinical seizures, or EEG features during hospitalization were associated with mortality during hospitalization, short-term and long-term neurologic deficits, or long-term cognitive outcomes (overall cognition, attention, memory) over the 2-year follow-up. Higher Blantyre or Glasgow Coma Scores (BCS and GCS, respectively), higher background voltage, and presence of normal reactivity on EEG were each associated with lower mortality. Among clinical and EEG features, the presence of >4 seizures on admission had the best combination of negative and positive predictive values for neurologic deficits in follow-up. In multivariable modeling of cognitive outcomes, the number of seizures and specific EEG features showed independent association with better outcomes. In children younger than 5 years throughout the study, seizure number and presence of vertex sharp waves were independently associated with better posthospitalization cognitive performance, faster dominant frequency with better attention, and higher average background voltage and faster dominant background frequency with better associative memory. In children younger than 5 years at CM episode but 5 years or older at cognitive testing, seizure number, background dominant frequency, and the presence of vertex sharp waves were each associated with changes in cognition, seizure number and variability with attention, and seizure number with working memory. In children with cerebral malaria, seizure number is strongly associated with the risk of long-term neurologic deficits, while seizure number and specific EEG features (average background voltage, dominant rhythm frequency, presence of vertex sharp waves, presence of variability) are independently associated with cognitive outcomes. Future studies should evaluate the predictive value of these findings.

ID 322 – Familial Creutzfeldt-Jakob disease. All night v-polysomnography study

Introduction The familial form of Creutzfeldt-Jakob disease (fCJD) is a dominantly inherited prion disease caused by mutations in the prion protein gene. We describe the sleep structure assessed by night v-polysomnography in a patient with Glu200Lys mutation. Patient A 53 y/o bus driver man came to hospital because of loss of memory. Seven months later disartria appeared, followed by ataxia and generalized myoclonus; the illness progressed to stupor and unresponsiveness and finally death after ten months. Results The first EEG showed a continuous focal right parietal epileptiform activity, with normal background activity. Two months later, a pattern of generalized synchronous periodic sharp waves appeared in the awake state. An all night video-polysomnography showed an abnormal sleep structure with no recognition of asleep stages; there were no vertex sharp waves nor spindles or K complex; with no REM sleep during awakenings the background activity was a diffuse low amplitude theta-delta activity, with generalized periodic bi-triphasic sharp waves. Abnormal respiratory events, were present with an apnea-hypopnea index of 79. Conclusion Night polysomnography in fCJD shows a very abnormal sleep structure, with a significant decrease in total sleep time, sleep efficiency, fragmentation, loss of normal sleep graphoelements, loss of REM sleep and periodic breathing with abnormal arousals.

Improving sensitivity of EEG–fMRI studies in epilepsy: The role of sleep-specific activity

Using simultaneous recordings of EEG and functional MRI (EEG–fMRI) in patients with focal epilepsy, recent studies have revealed insufficient sensitivity and a lack of correspondence between epileptic EEG foci and activation patterns in some patients. In this study of children with focal epilepsy, we explore whether sleep-specific activity (sleep spindles, k-complexes and vertex sharp waves) may increase the sensitivity of EEG–fMRI of interictal epileptiform discharges (IED). When considering the sleep-specific activity in a statistical model, it was possible to increase the statistical significance of the activated voxels inside of the expected source of the IED and to reduce the number of activated voxels outside of it. According to this study, it could be worthwhile to include sleep-specific activity into the model by analyzing EEG–fMRI data in epilepsy.

EEG-fMRI: Including sleep-induced potentials in the general linear model improves spatial accordance with epileptic focus

Introduction: Using EEG-fMRI in patients with focal epilepsy, recent studies have demonstrated that the spatial activation-patterns in fMRI associated with interictal epileptifirm discharges (IED) may correspond with epileptic focus. In this study we explore the influence of supplemental including sleep-related activities such as sleep spindles, k-complexes and vertex sharp waves, in the general linear model. The aim was to imvestigate whether this procedure may lead to an increase of significance or result in a better spatial accordance. Methods: We investigated 12 patients, 5–14 years of age (mean 9.3±2.84) with focal epilepsy using 3T fMRI (Philips-Archiva, anatomical T1*, 540 slices of EPI sequences) for about 20min by simultaneously 32-channel-EEG-recording (Brain Products, Gilching, Germany). All children were sedated (chloral hydrate) and in sleep stage 2. MRI-artifacts and ECG-artifacts were removed offline. Markers of IED and sleep-related activities such as sleep-spindles, k-complexes and vertex sharp waves were manually set. FMRI-data were preprocessed using SPM5 (realign, smoothing with 6mm) and normalized (expecting one female because of lesional damage). The first analysis included only epileptic discharges, used as events for the general linear model with canonical hemodynamic response function. The second analysis additionally included sleep-related activities. We compared the maximum t-values of each analysis, the total number of activated voxels and the changes of spatial accordance with the epileptic focus. Results: Compared to analysis 1, analysis 2 demnstrated no significant increment of the maximum t-values (t=0.81, p=0.435), as well as the total number of activated voxels (t=0.43, p=0.678). In 66.6% of cases in analysis 1 a spatial accordance were seen. By including sleep-related activities in the model the accordance increased up to 83.3% of cases. Conclusions: This study shows that including sleep-related activities does not lead to the increase of significance or to a significant change in the total number of activated voxels. But we observed that partially there is an increase of spatial accordance between epileptic focus and activation in fMRI.

The Visual Scoring of Sleep and Arousal in Infants and Children

Age is probably the single most crucial factor determining how humans sleep. Age and level of vigilance significantly influence the electroencephalogram (EEG) and the polysomnogram (PSG). The Pediatric Task Force provide an evidence-based review of the age-related development of the polysomnographic features of sleep in neonates, infants, and children, assessing the reliability and validity of these features, and assessing alternative methods of measurement. We used this annotated supporting text to develop rules for scoring sleep and arousals in infants and children. A pediatric EEG or PSG can only be determined to be normal by assessing whether the EEG patterns are appropriate for maturational age. Sleep in infants at term can be scored as NREM and REM sleep because all the polysomnographic and EEG features of REM sleep are present and quiet sleep, if not NREM sleep, is at least "not REM sleep." The dominant posterior rhythm (DPR) of relaxed wakefulness increases in frequency with age: (1) 3.5-4.5 Hz in 75% of normal infants by 3-4 months post-term; (2) 5-6 Hz in most infants 5-6 months post-term; 3) 6 Hz in 70% of normal children by 2 months of age; and 3) 8 Hz (range 7.5-9.5 Hz) in 82% of normal children age 3 years, 9 Hz in 65% of 9-year-olds, and 10 Hz in 65% of 15-year-old controls. Sleep spindles in children occur independently at two different frequencies and two different scalp locations: 11.0-12.75 Hz over the frontal and 13.0-14.75 Hz over the centroparietal electrodes; these findings are most prominent in children younger than 13 years. Centroparietal spikes are often maximal over the vertex (Cz), less often maximal over the left central (C3) or right central (C4) EEG derivation. About 50% of sleep spindles within a particular infant's PSG are asynchronous before 6 months of age, 30% at 1 year. Based on this, we recommend that: (1) sleep spindles be scored as a polysomnographic signature of NREM stage 2 sleep (N2) at whatever age they are first seen in a PSG, typically present by 2 to 3 months post-term; (2) identify and score sleep spindles from the frontal and centroparietal EEG derivations, especially in infants and children younger than 13 years. NREM sleep in an infant or child can be scored if the dominant posterior rhythm occupies 20% of the 30-second epoch contain 0.5 to 2 Hz >75 microV (usually 100-400 microV) activity as N3. The DPR should be scored in the EEG channel that is best observed, (typically occipital), but DPR reactive to eye opening can be seen in central electrodes. Because sleep spindles occur independently over the frontal and central regions in children, they should be scored whether they occur in the frontal or central regions. Because sleep spindles are asynchronous before age 2 years, simultaneous recording of left and right frontal and central activity may be warranted in children 1-2 years of age. Simultaneous recording of left, right, and midline central electrodes may be appropriate because of the asynchronous nature of sleep spindles before age 2 years, but reliability testing is needed. Evidence has shown that the PSG cannot reliably be used to identify neurological deficits or to predict behavior or outcome in infants because of significant diversity of results, even in normal infants. Normal sleep EEG patterns and architecture are present in the first year of life, even in infants with severe neurological compromise. Increasing evidence suggests that sleep and its disorders play critical roles in the development of healthy children and healthy adults thereafter. Reliability studies comparing head-to-head different scoring criteria, recording techniques, and derivations are needed so that future scoring recommendations can be based on evidence rather than consensus opinion. We need research comparing clinical outcomes with PSG measures to better inform clinicians and families exactly what meaning a PSG has in evaluating a child's suspected sleep disorder.

A Review of Sleep EEG Patterns. Part I: A Compilation of Amended Rules for Their Visual Recognition according to Rechtschaffen and Kales. Eine �bersicht �ber Schlaf-EEG-Muster. Teil I: Eine Zusammenstellung mit erg�nzenden Regeln zu deren visueller Analyse

The reliable evaluation of polysomnographic recordings (PSG) is an essential precondition for good clinical practice in sleep medicine. Although the scoring rules of Rechtschaffen and Kales [86] are internationally well established, they leave some room for different interpretations, and this may contribute to the limited reliability of visual sleep scoring. The German Sleep Society (DGSM) has set up a task force to devise ways to improve scoring reliability in the framework of their quality management programme. The intention was not to revise the rules of Rechtschaffen and Kales (R&K), but to facilitate their reliable application in sleep scoring and to support the development of standardized algorithms for computerized sleep analysis. The task force was formed in September 2004 as a subcommittee of the educational panel of the DGSM: The members of the task force are experienced in sleep scoring and have a background either in physiology, neurology, psychiatry, psychology, or biology. The aim of the task force was to provide interpretation aids and, if needed, specifications or amendments to the R&K rules for the scoring of sleep electroencephalogram (EEG) waveforms and patterns. Decisions were based on the nominal group technique of a nominal panel as the formal consensus-building process. The consensus process was based on scoring and face-to-face discussions of at least 40 examples for each pattern in four 2-day meetings. Relevant EEG patterns for sleep stage scoring are alpha, theta, and delta waves, sleep spindles, K-complexes, vertex sharp waves, and sawtooth waves. If definitions for a given EEG pattern differed in the literature, the nominal group technique resulted in specifications and amended scoring rules for these EEG patterns. A second part including a series of examples with explanatory comments for each of these EEG patterns is under preparation. Amendatory scoring rules of those EEG patterns that are relevant for sleep scoring may contribute to increasing the reliability of visual sleep scoring and to support the development of standardized algorithms for computerized sleep analysis.

Effects of Hypnagogic Imagery on the Event-Related Potential to External Tone0Stimuli

The purpose of this study was to examine the influence of hypnagogic imagery on the information processes of external tone stimuli during the sleep onset period with the use of event-related potentials. Event-related potentials to tone stimuli were compared between conditions with and without the experience of hypnagogic imagery. To control the arousal level when the tone was presented, a certain criterion named the electroencephalogram stage was used. Stimuli were presented at electroencephalogram stage 4, which was characterized by the appearance of a vertex sharp wave. Data were collected in the sleep laboratory at Hiroshima University. Eleven healthy university and graduate school students participated in the study. N/A. Experiments were performed at night. Reaction times to tone stimuli were measured, and only trials with shorter reaction times than 5000 milliseconds were analyzed. Electroencephalograms were recorded from Fz, Cz, Pz, Oz, T5 and T6. There were no differences in reaction times and electroencephalogram spectra between the conditions of with and without hypnagogic imagery. These results indicated that the arousal levels were not different between the 2 conditions. On the other hand, the N550 amplitude of the event-related potentials in the imagery condition was lower than in the no-imagery condition. The decrease in the N550 amplitude in the imagery condition showed that experiences of hypnagogic imagery exert some influence on the information processes of external tone stimuli. It is possible that the processing of hypnagogic imagery interferes with the processing of external stimuli, lowering the sensitivity to external stimuli.

Spindle coma from acute midbrain infarction

Spindle coma is an electroclinical entity in which physiologic sleep patterns, such as sleep spindles in the 9 to 14 Hz range, vertex sharp waves, and K complexes, superimposed on a background of delta and theta activity, occur synchronously in patients with altered consciousness.1 Spindle coma has been associated with structural (traumatic and nontraumatic) and nonstructural causes,2 such as cerebrovascular disease, tumor, surgery, hypoxia, seizure, drug intoxication, metabolic disturbances, and vasovagal syncope.2,3 We report three cases of spindle coma secondary to limited paramedian midbrain infarction, in which the prognosis was favorable. ### Patient 1. A 35-year-old woman presented with decreased consciousness. At the emergency room, she was comatose, with decreased and shallow respiratory effort. She had Takayasu’s disease, diagnosed 15 years previously, and was in remission. Neurologic examination showed vertical gaze ophthalmoplegia, loss of pupillary reflexes, and preserved flexor responses to pain with motor power of Medical Research Council (MRC) grade 2/5. Brain MRI revealed an isolated right paramedian midbrain infarction with thrombosis at the distal …

Slow horizontal eye movement at human sleep onset.

Slow eye movement (SEM) at human sleep onset has been studied as a function of EEG and behavioral state but has not been subjected to systematic physical measurement. This study counted the frequency of horizontal SEM and quantified its physical properties during hypnagogic EEG stages 3-8 (stage 1 sleep). SEM amplitudes, peak velocities, and durations were digitally measured. As in previous studies SEM occurred throughout stage 1 sleep, coinciding with all tonic states and with all phasic events that classically define stage 1. Within stage 1 the physical properties of SEM varied significantly. In hypnagogic stage 3, where EEG alpha dominates up to half of any 30-s epoch, the typical SEM was moderate in amplitude, slow, and short-lasting, and SEM peak velocity described a weak function of SEM amplitude. In stages 5 and 6 combined--characterized by a low-voltage delta-theta EEG, sustained alpha suppression, and no more than one vertex sharp wave (VSW) per 30-s epoch--SEM velocity was maximal, and described a strong function of amplitude. Despite low absolute velocities, stage 5/6 SEM could approximate saccade-like morphologies. In stages 7 and 8 combined, characterized by VSW bursts and incipient spindles or K complexes, SEM was maximal in amplitude and duration but not faster than SEM in stage 5/6. These properties of human SEM are discussed in relation to the anatomy and physiology of SEM in macaque.

Increased Production of Evoked and Spontaneous K-complexes Following a Night of Fragmented Sleep

To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. A 3-night study--night 1 as a baseline night, night 2 as a sleep fragmentation night, followed immediately by night 3 as a recovery night. On nights 1 and 3, approximately 400 auditory stimuli were presented during nonREM sleep in the first two sleep cycles, using stimulus parameters previously found to be optimal for K-complex production. The sleep research laboratory at the University of Melbourne. Six young healthy subjects (3 female). One night of sleep fragmentation. Ten-second auditory tones of up to 110 dB were presented throughout the entire night at approximately 1-minute intervals. Sleep drive was increased on the recovery night, as indicated by increased amounts of slow wave sleep, increased sleep efficiency, and a reduction in stimulus-related alpha activity. The incidence of both evoked and spontaneous K-complexes increased significantly on the recovery night. When K-complex trials were averaged, neither N550 (Fz) amplitude nor latency differed between the 2 nights. When vertex sharp waves were averaged, N350 (Cz) amplitude was increased significantly on the recovery night. The increase in K-complex frequency together with the decrease seen in stimulus-related alpha activity supports the view that they reflect a sleep maintenance, rather than an arousal, response.

Evoked potential components unique to non-REM sleep: relationship to evoked K-complexes and vertex sharp waves

Following the loss of wakeful consciousness, the averaging of responses to stimuli produce evoked potential waveforms with prominent components either unique to or greatly enhanced by non-REM sleep. In the sleep onset periods (stage 1) these are the P2 and N350. Following the establishment of stable sleep (stage 2 and SWS), the N550 and P900 are also prominent. Investigation of the EEG associated with individual responses indicates that a good proportion of stimuli elicit, K-complexes or vertex sharp waves (VSWs) and occasionally will elicit both. Recent work has indicated that the N550 in the averaged response is due to the presence of K-complexes and that the N350 is at least largely due to the presence of VSWs. The large size of these grapho-elements indicates that they are probably produced by a synchronized discharge of multiple neural units. Both are readily observed in the absence of external stimulation and occur as normal components of sleep, indeed the K-complex is used as one of the identifying features of the onset of stable non-REM sleep. The present review details the investigation of these features and their associated evoked potential components, in terms of stimulus features, brain states associated with their production, their scalp topography, and changes as a function of age.

Effect of sleep deprivation on NREM sleep ERPs and related activity at sleep onset

This research assessed the impact of one night of sleep deprivation on the amplitudes of NREM-sleep event-related potentials (NREM ERPs) and on the frequency of occurrence of related electroencephalogram activity including sleep spindles, arousals, K-complexes, and vertex sharp waves (VSWs). The NREM ERPs identified included P220, N350, P450, N550 and P900. During a pre-deprivation night, ten subjects took two 20-min naps separated by a 20-min break at their normal bedtime. Brief tones were presented at three intensity levels (60, 75 and 90 dB) with a 5-s interstimulus interval. Following these naps, subjects were kept awake until their normal bedtime the following day. At that time, they repeated the two-nap procedure. The ERPs obtained for each tone and wake/sleep state for pre- and post-deprivation conditions were analyzed using repeated measures statistical procedures. As anticipated, NREM ERP amplitudes recorded both pre- and post-deprivation increased with tone intensity and with approaching sleep. Also, sleep deprivation was associated with more rapid sleep onset, reduced arousability, and greater spindle production. While sleep deprivation had no effect on the amplitude of P220. Post-deprivation amplitudes of N350, N550 and P900 were greater, especially following the 90-dB tone. There was a corresponding increase in VSWs and K-complexes. These findings are inconsistent with the view that NREM ERPs reflect arousal. The underlying mechanism(s) may facilitate initiation and maintenance of sleep.

Event-related potential measures of the inhibition of information processing: II. The sleep onset period

The loss of consciousness during the sleep onset period is associated with dramatic changes in information processing. Human event-related potentials (ERPs) reflect these changes. Short- and mid-latency ERPs are only minimally affected by sleep onset. On the other hand, long-latency ERPs are very much affected. A negative wave, N1, peaking at approximately 100 ms gradually decreases in amplitude until it reaches baseline level during definitive stage 2 sleep. The changes in N1 are especially apparent when the subject no longer signals awareness of the external stimulus or when stage 1 is dominated by theta activity in the EEG. The positive peaks, P1 and P2, peaking at approximately 50 and 180 ms, respectively, may appear to increase in amplitude (i.e. also be less negative). A long-lasting processing negativity (PN) may overlap and summate with these peaks during the waking state. During sleep onset, the PN dissipates, thus explaining the apparent positive baseline shift in the ERP waveform. In an oddball task, when an alert and awake subject detects a rare, relevant stimulus, a large positive wave, P300, maximum over parietal areas of the scalp, is observed. This P300 is, however, widely dispersed and can be observed over frontal areas of the scalp. When the subject no longer signals detection of this target stimulus, P300 can no longer be recorded. During stage 1, the parietal P300 remains large, providing the subject overtly detects the target. The amplitude of the frontal aspect of P300 is much reduced as response times slow. This may reflect deactivation of the frontal lobes during the sleep onset period. The infrequent change of an otherwise rapidly presented homogenous train of stimuli is associated with another long-lasting negativity, the mismatch negativity (MMN). The MMN also decreases in amplitude during the sleep onset period, reaching baseline level during definitive sleep. The vertex sharp wave (VSW) becomes apparent during the sleep onset period. Associated with the VSW is a late negative ERP, sometimes called the sleep N2 or the N350, peaking between 300 and 350 ms. It is unique to the sleep onset and sleep periods, becoming very large during stage 1-theta or when the subject no longer shows signs of awareness of the external stimulus.

Spindle coma secondary to vasovagal syncope

Spindle coma refers to unconsciousness in association with an electroencephalographic pattern of ‘‘sleep-like’’ activity characterized by spindles in the range 9–14 Hz, intermixed with vertex sharp waves and K-complexes [1]. The first description involved a patient with a tumor infiltrating the hypothalamus and the midbrain near the third ventricle, sparing the thalamus [2]. Spindle coma was later observed in patients with closed head injury [3] and anoxic encephalopathy [4,5] and, more recently, measles encephalitis [6], viral meningoencephalitis [7], drug intoxication (ethanol and imipramine), and diverse structural insults, suggesting that the pattern is nonspecific without prognostic significance [8,9]. A peculiar 11to 14-Hz frontal spindle rhythm with preserved posterior background frequencies has been observed in patients with nontraumatic diffuse encephalopathy with only slightly impaired consciousness [5]. The sites responsible for spindle generation in humans are located in the thalamus and superior frontal regions. In those patients with spindle coma associated with lesions, the characteristic location of the pathology is between the pontomesencephalic junction and thalamus [8,10]. Whereas patients have intact cortical function, they are unarousable because of predominant impairment of the ascending reticular formation at the level of the midbrain. Further, there is no interference with the basic mechanisms of sleep, especially NREM sleep, because the pontine raphe nuclei are typically intact [11,12]. We report a case of spindle coma in a young woman with reversible hypoxic encephalopathy following vasovagal syncope. 2. Case report

An examination of evoked K-complex amplitude and frequency of occurrence in the elderly.

The elderly consistently display lower levels of slow wave sleep (SWS), primarily because of the small amplitude of their delta activity. Given that delta electroencephalogram (EEG) and K-complexes are thought to be generated by the same mechanisms, it was hypothesized that K-complex amplitude and rate of production would be lower in the elderly. K-complex amplitude was assessed by averaging K-complex responses to auditory stimuli, and measuring the amplitude of the N550 component of the averaged evoked response. Ten young (five males and five females; mean age 23.10 +/- 5.36 years) and 10 elderly adults (six males and four females; mean age=75.60 +/- 4.48 years) who were neurologically healthy and free from medication spent two non-consecutive nights in the sleep laboratory. EEG was recorded from six gold plate electrodes (Fz, Fcz, Cz, Cpz, Pz and O2) referenced to A1 + A2. Tone clicks (1000 Hz), of varying intensity from 70 to 100 decibels above measured awake detection threshold, were presented binaurally during stage 2 sleep. Responses were classified according to whether they produced: a K-complex, a vertex sharp wave (VSW), both of these responses or neither response. They were then averaged separately for each response type. The elderly showed a substantially smaller N350 (averaged VSWs) and N550 amplitudes compared with the young subjects. The elderly also showed an augmented but delayed P2 component, followed by a long-lasting positive EEG shift. The smaller amplitude of the averaged K-complex N550 component is consistent with lower delta amplitudes previously reported in the elderly and with the hypothesis that K-complexes and delta activity share the same generator mechanisms. The enhanced P2 component and the long-lasting positive deflection in the EEG in the elderly indicate the existence of age differences other than smaller EEG amplitude.

A negative component superimposed on event-related potentials during light drowsiness.

The present study examined the nature of the negative shift of event-related potential (ERP) recorded during the fully awake state, wakefulness with minor awareness deficit (light drowsiness) and stage 1 of NREM sleep. The cortical responses evoked by two types of auditory stimuli were recorded in nine subjects at the different levels of consciousness described above. A negative component with peak latency of 250-350 msec, N300, was identified in ERP during light drowsiness but not in the fully awake state. In stage 1a (stage 1 without vertex sharp waves), the amplitude of N300 was higher than that in light drowsiness, and it was higher in stage 1b than in stage 1a. The scalp distribution of N300 was predominantly on the vertex. It also confirmed that the vertex sharp wave evoked during stage 1 is maximal on the vertex and its peak latency is approximately 300 msec. Considering the similarity in scalp distribution and peak latency between N300 and vertex sharp wave, it is possible that these electroencephalogram phenomena are generated by an identical synchronizing mechanism in the brain. We assumed that N300 observed during light drowsiness may be an incomplete product of vertex sharp wave.

The process of falling asleep.

The process of falling asleep can best be measured by considering a convergence of behavioural, EEG, physiological and subjective information. Doing so allows one to see sleep processes as they unfold, but relying on any single sleep index can bias the description of this complex process. The studies reviewed do not support the idea that sleep begins "in a moment", but rather that entry into sleep is a continuous, interwoven series of changes which begin in relaxed drowsiness and continue through stage 1, often into the first minutes of stage 2. The transition from waking brain to sleeping brain is traced accurately by Hori's nine-stage EEG system. Event-related potential (ERP) studies map complex changes in information processing as sleep begins, while quantitative EEG investigations have identified important spatiotemporal re-organisations of primary EEG frequencies which take place as one moves from waking to sleeping mode. To consider evidence from multiple levels of analysis, a three step electrophysiological model of central nervous system (CNS) regulation during sleep onset is proposed: initial processes appear to be alpha-related; intermediate processes, poorly studied to date, parallel the development of theta and vertex sharp wave activity, while the processes which terminate wakefulness are sigma sleep spindle-related. Clinical investigations of the sleep onset period in people with narcolepsy, insomnia, depression or sleep apnoea appear to indicate the presence of relatively unique electrophysiological signatures which may be of clinical significance. 2001 Harcourt Publishers Ltd

The investigation of K-complex and vertex sharp wave activity in response to mid-inspiratory occlusions and complete obstructions to breathing during NREM sleep.

To determine whether the cortical response to mid-inspiratory occlusions can be used as a model of the cortical response to obstructive events during sleep; and to determine whether the vertex sharp wave (VSW) and K-complex are exclusive contributors to the N350 and N550 components respectively of the stage 2 sleep event-related potential. Two types of respiratory stimuli were used to elicit evoked potential responses during stage 2 NREM sleep. These were mid-inspiratory occlusions and complete breath obstructions. Trials were grouped according to the type of phasic response elicited; isolated K-complex (KC), VSW associated with a K-complex (VSW/KC), isolated VSW, and no evoked response (other). Evoked responses were averaged separately within these categories. Data were collected in the University of Melbourne Sleep Laboratory. Six young healthy male adults. N/A. Data were recorded from 29 scalp sites referenced to linked ears. Mask pressure (Pm) and airflow were also recorded. Intra-thoracic pressure, as indicated by Pm, reached a more negative level following complete obstructions than brief occlusions. However, both types of respiratory stimuli elicited the two late latency components. Although latency varied across the two respiratory conditions in a manner consistent with the intra-thoracic pressure rise time differences, the elicitation characteristics and topographic distribution of these components did not vary across the two types of stimuli. In addition, an N350 was only present in the average for those categories that included VSWs, while an N550 was only present in those categories that contained K-complexes. Mid-inspiratory occlusions can be used as a model of obstructive events. VSWs contribute exclusively to the N350 component, while K-complexes contribute exclusively to the N550 component.

Topographical characteristics of slow wave activities during the transition from wakefulness to sleep

Objectives: This study examined the topographical characteristics of slow wave(delta and theta) activities during the transition from wakefulness to sleep, using topographic mapping of EEG power and coherence.Methods: Sonography of nocturnal sleep was recorded on 10 male subjects. Each recording, from ‘lights-off’ to 5 min after the appearance of the first sleep spindles, was analyzed. Typical EEG patterns during the transition from wakefulness to sleep were classified into 9 stages (EEG stages).Results and conclusions: Topographic maps of coherence in delta-and theta-band activities demonstrated that the synchronous component at the anterior-central areas of the scalp appeared corresponding with increasing power. The populations of high coherence pairs among total pairs were computed for each band and each EEG stage to examine the regional differences of EEG. The populations of the delta-band activity increased clearly from EEG stage 6 in the anterior-central areas. The populations of the theta-band activity increased clearly from EEG stage 7 in the anterior-central areas. These results suggest that the dominant synchronous component of slow wave activities during the transition from wakefulness to sleep increased as a function of EEG stages in the anterior-central areas and increased clearly after the appearance of vertex sharp waves.

The Roles of Vertex Sharp Waves and K-Complexes in the Generation of N300 in Auditory and Respiratory-related Evoked Potentials During Early Stage 2 NREM Sleep

To determine the scalp topography of the N300 response to stimuli of different modalities and to investigate the relationship of the N300 component to K-complexes and vertex sharp waves seen in the un-averaged EEG. Two experiments were conducted one using auditory; the other using respiratory occlusion stimuli presented during stage 2 sleep. Trials were classified on the basis of whether they produced a K-complex, a vertex sharp wave, or some other response. Auditory stimuli were presented in the form of an oddball paradigm, and averaged separately depending on whether they were "frequent" or "rare". In both experiments, responses were averaged separately based on the appearance of K-complexes, vertex sharps waves, or some "other" response to the stimuli. Data were collected in the Melbourne University Sleep Laboratory. Young healthy male adults, eight in experiment 1 and six in experiment 2. NA. Data were collected from 29 scalp sites. In all cases, N300 amplitude was maximal in the vertex sharp wave averages, despite being clearly present in the averages of K-complexes and "other" responses. The vertex maximal scalp topography of the N300 did not differ across response conditions or as a function of stimulus modality. This is consistent with the N300 being produced by the same intracranial generators in all cases. There were no effects of stimulus or response type on N300 latency. N300 should be viewed as a multi-modal component with a different underlying generator mechanism than that of the K-complex.