Ontogeny of delta activity during human sleep

The Future of Sleep Staging, Revisited

In 1996, I published a paper entitled "The Future of Sleep Staging". At this time, paper and ink records were the standard way of recording sleep records. Computerised systems had only recently become commercially available. The original article was a response to those initial computer-based systems, pointing out the potential limitations of the systems. Now, digital sleep recording is ubiquitous and software and hardware capabilities have improved immeasurably. However, I will argue that despite 50 years of progress, there has not been an increase in the accuracy of sleep staging. I will propose that this is due to the limitations of the task that we have set the automatic analysis methods.

Interrater reliability of sleep stage scoring: a meta-analysis

STUDY OBJECTIVES

We evaluated the interrater reliabilities of manual polysomnography sleep stage scoring. We included all studies that employed Rechtschaffen and Kales rules or American Academy of Sleep Medicine standards. We sought the overall degree of agreement and those for each stage.

METHODS

The keywords were "Polysomnography (PSG)," "sleep staging," "Rechtschaffen and Kales (R&K)," "American Academy of Sleep Medicine (AASM)," "interrater (interscorer) reliability," and "Cohen's kappa." We searched PubMed, OVID Medline, EMBASE, the Cochrane library, KoreaMed, KISS, and the MedRIC. The exclusion criteria included automatic scoring and pediatric patients. We collected data on scorer histories, scoring rules, numbers of epochs scored, and the underlying diseases of the patients.

RESULTS

A total of 101 publications were retrieved; 11 satisfied the selection criteria. The Cohen's kappa for manual, overall sleep scoring was 0.76, indicating substantial agreement (95% confidence interval, 0.71-0.81; P < .001). By sleep stage, the figures were 0.70, 0.24, 0.57, 0.57, and 0.69 for the W, N1, N2, N3, and R stages, respectively. The interrater reliabilities for stage N2 and N3 sleep were moderate, and that for stage N1 sleep was only fair.

CONCLUSIONS

We conducted a meta-analysis to generalize the variation in manual scoring of polysomnography and provide reference data for automatic sleep stage scoring systems. The reliability of manual scorers of polysomnography sleep stages was substantial. However, for certain stages, the results were poor; validity requires improvement.

CITATION

Lee YJ, Lee JY, Cho JH, Choi JH. Interrater reliability of sleep stage scoring: a meta-analysis. J Clin Sleep Med. 2022;18(1):193-202.

Optimizing computation of overnight decline in delta power: Evidence for slower rate of decline in delta power in insomnia patients

OBJECTIVE

To determine the best of commonly used methods for computing the rate of decline in non-rapid eye movement (NREM) sleep EEG delta power overnight (Delta Decline) in terms of vulnerability to missing data and to evaluate whether this rate is slower in insomnia patients than healthy controls (HC).

METHODS

Fifty-one insomnia patients and 53 HC underwent 6 nights of polysomnography. Four methods for estimating Delta Decline were compared (exponential and linear best-fit functions using NREM (1) episode mean, (2) peak, and (3) total delta power and (4) delta power for all available NREM epochs). The best method was applied to compare groups on linear and exponential rates of Delta Decline.

RESULTS

Best-fit models using all available NREM epochs were significantly less vulnerable to deviation due to missing data than other methods. Insomnia patients displayed significantly slower linear and exponential Delta Decline than HC.

CONCLUSIONS

Computing Delta Decline using all available NREM epochs was the best of the methods studied for minimizing the effects of missing data. Insomnia patients display slower Delta Decline, which is not explained by differences in total sleep time or wake after sleep onset.

SIGNIFICANCE

This study supports using all available NREM epochs in Delta Decline computation and suggests a slower rate in insomnia.

Human longevity is associated with regular sleep patterns, maintenance of slow wave sleep, and favorable lipid profile

Some individuals are able to successfully reach very old ages, reflecting higher adaptation against age-associated effects. Sleep is one of the processes deeply affected by aging; however few studies evaluating sleep in long-lived individuals (aged over 85) have been reported to date. The aim of this study was to characterize the sleep patterns and biochemical profile of oldest old individuals (N = 10, age 85–105 years old) and compare them to young adults (N = 15, age 20–30 years old) and older adults (N = 13, age 60–70 years old). All subjects underwent full-night polysomnography, 1-week of actigraphic recording and peripheral blood collection. Sleep electroencephalogram spectral analysis was also performed. The oldest old individuals showed lower sleep efficiency and REM sleep when compared to the older adults, while stage N3 percentage and delta power were similar across the groups. Oldest old individuals maintained strictly regular sleep-wake schedules and also presented higher HDL-cholesterol and lower triglyceride levels than older adults. The present study revealed novel data regarding specific sleep patterns and maintenance of slow wave sleep in the oldest old group. Taken together with the favorable lipid profile, these results contribute with evidence to the importance of sleep and lipid metabolism regulation in the maintenance of longevity in humans.

Cortical regional differences of delta waves during all-night sleep in schizophrenia

BACKGROUND

Delta sleep is mediated by thalamocortical circuits and is postulated to be abnormal in schizophrenia. Delta wave deficits during sleep have been observed in patients with schizophrenia. Negative symptoms have been reported to reflect frontal lobe dysfunction and to be associated with decreased delta wave sleep. This investigation was undertaken to identify cortical functional abnormalities in patients with schizophrenia shown on the electroencephalogram.

METHODS

We compared seventeen male, medically treated or neuroleptic-naive outpatients with schizophrenia and 18 healthy male volunteers by all-night polysomnography and investigated cortical regional differences of delta waves. All-night sleep data was evaluated by period amplitude analyses. Delta waves during sleep were investigated in bilateral frontal, central, parietal, and occipital regions by computer analysis. The associations between delta waves in all regions and measures of clinical variables were also estimated.

RESULTS

Patients with schizophrenia showed lower total delta wave counts during all-night sleep than did control subjects in all regions. Control subjects showed significantly higher delta wave counts in the right frontal and central region than in the left, which was not observed in patients with schizophrenia. Significant inverse correlations were observed between negative symptom scores and delta wave counts in all regions. Control subjects showed significant inverse correlations between delta wave counts and age, which were not identified in patients with schizophrenia.

CONCLUSIONS

Delta wave deficits in all regions may reflect thalamocortical dysfunction in schizophrenia. Reduced right frontal and central delta wave dominance is suggested to be involved in the pathophysiology of schizophrenia.

Sleep EEG predictors and correlates of the response to cognitive behavioral therapy for insomnia

STUDY OBJECTIVES

Determine the relationship of non-rapid eye movement (NREM) electroencephalographic (EEG) spectral measures and the response to cognitive behavioral therapy (CBT) in primary insomnia (PI).

DESIGN

Patients with PI were randomly assigned to CBT or a placebo intervention (PC). Ambulatory polysomnography was performed before and after treatment.

SETTING

University medical center sleep laboratory.

PARTICIPANTS

Thirty PI patients with sleep maintenance difficulty evident in subjective sleep measures.

INTERVENTIONS

CBT and PC.

RESULTS

CBT led to a more rapid decline in EEG delta power over the night, compared with PC. This change was associated with subjective improvement in response to CBT. Furthermore, lower pretreatment peak EEG delta power in the first NREM cycle and a more gradual decline in delta power predicted a better response to CBT. Increased wake time during the day produced by CBT was correlated with an increase in the steepness of the slope of EEG delta power and subjective improvement. Traditional polysomnography measures were associated with the subjective CBT response to a greater degree among patients whose total sleep time estimates better approximated polysomnography-derived total sleep time. In contrast, changes in all-night averaged NREM EEG spectral indices were more strongly related to subjective improvement in individuals who underestimated total sleep time to a greater extent.

CONCLUSIONS

CBT led to a more rapid decline in EEG delta power over the night. This change is linked to the therapeutic effect of CBT, which appears to occur in conjunction with an increase in homeostatic sleep drive. Traditional polysomnography indices and all-night averaged NREM EEG measures appear to be related to subjective improvements with CBT in subsets of patients with PI.

Sleep evoked delta frequency responses show a linear decline in amplitude across the adult lifespan

Aging is associated with many changes in sleep, with one of the most prominent being a reduction in slow wave sleep. Traditional measures of this phenomenon rely on spontaneous activity and typically confound the incidence and amplitude of delta waves. The measurement of evoked K-complexes during sleep, enable separate assessment of incidence and amplitude taken from the averaged K-complex waveform. The present study describes data from 70 normal healthy men and women aged between 19 and 78 years. K-Complexes were evoked using short auditory tones and recorded from a midline array of scalp sites. Significant reductions with age were seen in the amplitude of the N550 component of the averaged waveform, which represents the amplitude of the K-complex, with linear regression analysis indicating approximately 50% of the variance was due to age. Smaller, yet still significant reductions were seen in the ability to elicit K-complexes. The data highlight the utility of evoked K-complexes as a sensitive marker of brain aging in men and women.

Aging-related sleep changes

Normal aging is accompanied by changes in the sleep quality, quantity, and architecture. Specifically, there appears to be a measurable decrease in the ability of the healthy elderly to initiate and maintain sleep, accompanied by a decrease in the proportion of the deeper, more restorative slow-wave sleep and rapid eye movement sleep. There is epidemiologic evidence that this impaired ability to initiate, maintain, and ultimately achieve good quality, optimal sleep may be a marker of increased mortality and neurocognitive dysfunction. Possible mechanisms related to these age-related changes in sleep include age-related changes in circadian modulation, homeostatic factors, cardiopulmonary function, and endocrine function. This article describes the normal changes in sleep physiology in the elderly.

Reduced frontal asymmetry of delta waves during all-night sleep in schizophrenia

Delta wave deficits during sleep have been observed in patients with schizophrenia. Decreased slow-wave sleep is reported to be associated with negative symptoms. Frontal lobe dysfunction is also believed to underlie negative symptoms of schizophrenia. This study was designed to identify functional abnormalities in schizophrenia manifested on patients' electroencephalograms. Polysomnograph examinations were performed in 12 healthy male volunteers and 11 male outpatients with schizophrenia. We investigated the laterality of frontal cortical delta waves in patients with schizophrenia and in healthy control subjects. Laterality of frontal cortex delta wave counts during all-night sleep was investigated by computer analysis. Total delta wave counts were lower in patients with schizophrenia than in control subjects. Control subjects showed significantly higher delta wave counts in the right frontal cortex than in the left. This asymmetry was not observed in patients with schizophrenia. These findings suggest that reduced right frontal delta wave dominance is involved in the pathophysiology of schizophrenia.

Sleep spindle evolution from infancy to adolescence

OBJECTIVE

To investigate the development of frontally recorded sleep spindles from infancy to adolescence to provide normative data for pediatric sleep medicine.

METHODS

Sleep spindle activity was investigated in 120 healthy subjects aged 3 months to 16 years in 12 age groups. At 2 a.m. (min 1:17 a.m., max 3:18 a.m.) 10 min of NREM 2 was checked. Spindles were visually scored in the electroencephalogram from F4/A1.

RESULTS

The age dependency of interspindle interval, length of spindle, and spindle density, was statistically significant (Kruskal-Wallis p<0.0001). There were U-shaped curves for spindle length, spindle density, and an inverted U-shaped curve for the interspindle interval. Results of the post hoc U-test p<0.05 (Bonferroni corrected, m=66): Spindle length was minimal at 1.7 up to 3.0 years. Spindle density (number of spindles) was minimal between the ages of 1.7 and 2.3 years, thereafter there was a high increase that reached a plateau at age 5 years and remained up to 16 years. Interspindle interval was maximal at 1.7 and 2.3 years.

CONCLUSIONS

Sleep spindle activity changes with maturation in terms of length and density.

SIGNIFICANCE

The establishment of age-related normative data of sleep spindle activity can improve identification of NREM 2 in infancy, childhood, and adolescence, and enable detection of delayed neural maturation and/or sleep instability.

Sleep in Critically Ill Chemically Paralyzed Patients Requiring Mechanical Ventilation

OBJECTIVE

To determine sleep characteristics in patients receiving mechanical ventilation who require a neuromuscular blocking agent (NMBA).

DESIGN

Observational study.

SETTING

Adult medical ICU at a university hospital.

PARTICIPANTS

Eighteen patients with respiratory failure requiring mechanical ventilation were classified into three groups based on medication regimen determined a priori: intermittent sedation (IS), continuous sedation (CS), or CS and an NMBA.

MEASUREMENTS

Twenty-four-hour polysomnography was performed to determine sleep architecture and fragmentation. Measurement of severity of illness, laboratory indexes, patient-care interventions, and drug dosage were compared between groups, and the effects on sleep staging and fragmentation were analyzed. Sleep stages were scored manually using criteria of Rechtschaffen and Kales, as well as by a modified 50-muV voltage criteria for scoring delta activity.

RESULTS

All patients demonstrated abnormal sleep architecture. In each group of patients, the total sleep time (TST) was > 10 h. There was no statistical difference in the delta activity between the two scoring methods; delta activity was increased in all groups: 32.9%, 49.6%, and 43.7% in the IS, CS, and CS/NMBA groups, respectively. Patients receiving NMBAs spent 22% of the sleep period awake. Rapid eye movement sleep could not be detected in the patients receiving NMBAs and was reduced in the other two groups (3.5%). TST, sleep stage, or arousal/awakening index were not statistically correlated with either severity of illness, clinical laboratory indexes, drug dosage, patient-care interventions, or mode of mechanical ventilation.

CONCLUSION

TST during a 24-h period is not reduced in patients requiring mechanical ventilation. Delta activity is increased and may reflect age, drug, or a contributing metabolic process. The effect of wakefulness in patients receiving chemical paralysis on recovery and weaning from mechanical ventilation, and overall clinical outcome is unknown.

Regional differences of the sleep electroencephalogram in adolescents

The sleep electroencephalogram (EEG) was recorded from anterior (Fz/Cz) and posterior (Pz/Oz) bipolar derivations in two developmental groups: 20 pre- or early pubertal (Tanner 1/2, mean age 11.4 +/- 1.1 years, 11 boys) and 20 late pubertal or mature adolescents (Tanner 4/5, 14.1 +/- 1.3 years, 8 boys). A sleep-state independent reduction of EEG power over almost the entire frequency range was present in Tanner 4/5 compared with Tanner 1/2 adolescents. Spectral characteristics of the sleep EEG yielded state- and frequency-dependent regional differences that were similar in both developmental groups. Anterior predominance of power in delta and sigma ranges occurred in non-rapid eye movement sleep. Rapid eye movement sleep EEG power was greater in low delta, alpha, and sigma ranges for the posterior derivation and in theta and beta ranges for the anterior derivation. The decay rate of the sleep homeostatic process--reflected by the exponential decline of the 2-Hz EEG power band across the sleep episode--did not differ for derivations or groups. These results indicate that the nocturnal dynamics of sleep homeostasis are independent of derivation and remain stable across puberty.

The frontal predominance in human EEG delta activity after sleep loss decreases with age

Sleep loss has marked and selective effects on brain wave activity during subsequent recovery sleep. The electroencephalogram (EEG) responds to sleep deprivation with a relative increase in power density in the delta and theta range during non-rapid eye movement sleep. We investigated age-related changes of the EEG response to sleep deprivation along the antero-posterior axis (Fz, Cz, Pz, Oz) under constant routine conditions. Both healthy young (20-31 years) and older (57-74 years) participants manifested a significant relative increase in EEG power density in the delta and theta range after 40 h of sleep deprivation, indicating a sustained capacity of the sleep homeostat to respond to sleep loss in ageing. However, the increase in relative EEG delta activity (1.25-3.75 Hz) following sleep deprivation was significantly more pronounced in frontal than parietal brain regions in the young, whereas such a frontal predominance was diminished in the older volunteers. This age-related decrease of frontal delta predominance was most distinct at the beginning of the recovery sleep episode. Furthermore, the dissipation of homeostatic sleep pressure during the recovery night, as indexed by EEG delta activity, exhibited a significantly shallower decline in the older group. Activation of sleep regulatory processes in frontal brain areas by an extension of wakefulness from 16 to 40 h appears to be age-dependent. These findings provide quantitative evidence for the hypothesis that frontal brain regions are particularly vulnerable to the effects of elevated sleep pressure ('prefrontal tiredness') and ageing ('frontal ageing').

Association between delta waves during sleep and negative symptoms in schizophrenia. Pharmaco-eeg studies by using structurally different hypnotics

We examined the effects of benzodiazepine (BZD) hypnotics and zopiclone (ZPC), a nonbenzodiazepine hypnotic, on sleep and psychiatric symptoms in schizophrenia, as well as the clinical correlates of these variables. Seven male schizophrenic patients chronically taking neuroleptics together with BZD were studied. We replaced BZD with ZPC and performed polysomnography (PSG) and Brief Psychiatric Rating Scale (BRPS) scoring before and after an 8-week ZPC treatment. The replacement of BZD with ZPC increased the mean amplitude of high-amplitude low-frequency delta waves on the frontal derivation recognized by period-amplitude analysis, and it decreased the BPRS negative-symptom score. Under the BZD treatment, the negative-symptom score correlated inversely with the mean amplitude of high-amplitude low-frequency delta waves. This correlation was weak and not significant under the ZPC treatment. Therefore, delta waves during sleep have a close correlation to negative symptoms in schizophrenia, and such a correlation could be influenced by hypnotics. Although these are preliminary findings, it was suggested that, compared with BZD, ZPC might be a beneficial hypnotic in regard to both sleep and negative symptoms of chronic schizophrenic patients.

Asymmetric interhemispheric delta waves during all-night sleep in humans

OBJECTIVE

In order to better understand the asymmetry of brain function during sleep, period-amplitude analysis of delta EEG activity was performed on polysomnograms (PSGs) in normal humans. Twenty healthy, right-handed male volunteers aged 22-35 years (mean age 27.2 years) served as subjects in this study.

METHODS

EEGs were recorded from disc electrodes placed at bilateral frontal, central, parietal, occipital, anterotemporal and posterotemporal (10-20 electrode system) sites using A1+A2 for reference. Period-amplitude analysis was performed by the zero-crossing method using the Medilog Sleep Analyzing Computer.

RESULTS

Delta counts in the right frontal and central regions during all-night sleep were significantly greater than in those of the left; total delta counts of the right frontal region were greater than those of the left in 18 of the 20 subjects. There were no significant differences in delta counts between the left and right hemispheres in parietal, occipital, anterotemporal, and postero-temporal regions.

CONCLUSIONS

These results suggest distinct laterality in the number of delta waves in the frontal and central regions, reflecting functional asymmetry of the brain during sleep.

Laterality of delta waves during all-night sleep

In order to clarify the functional asymmetry of the brain function during sleep, period-amplitude analysis of delta electroencephalogram activity was performed on polysomnograms in 12 right-handed healthy males. Electroencephalograms were recorded from disc electrodes placed at C3, C4, O1 and O2 (10-20 electrode system), using A1 +A2 for reference. Although there were no significant differences in delta counts between O1 and O2, delta counts of C3 were significantly larger than those of C4. These results suggest that there exists distinct laterality in the number of delta waves in the central region, reflecting the functional asymmetry of the brain during sleep.

Effect of age on the sleep EEG: slow-wave activity and spindle frequency activity in young and middle-aged men

The effect of age on sleep and the sleep EEG was investigated in middle-aged men (mean age: 62.0 years) and in young men (mean age: 22.4 years). Even though the older men reported a higher number of nocturnal awakenings, subjective sleep quality did not differ. Total sleep time, sleep efficiency, and slow wave sleep were lower in the middle-aged, while stage 1 and wakefulness after sleep onset were higher. The differences in wakefulness within nonREM-REM sleep cycles was most pronounced in the third and fourth cycle. In the older men, EEG power density in nonREM sleep was reduced in frequencies below 14.0 Hz, whereas in REM sleep age-related reductions were limited to he delta-theta (0.25-7.0 Hz) and low alpha (8.25-10.0 Hz) band. Slow-wave activity (SWA, power density in the 0.75-4.5 Hz range) decreased in the course of sleep in both age groups. The between-group difference in SWA diminished in the course of sleep, whereas the difference in activity in the frequency range of sleep spindles (12.25-14.0 Hz) increased. It is concluded that frequency and state specific changes occur as a function of age, and that sleep dependent decline in SWA and increase in sleep spindle activity are attenuated with age.

A quantitative sleep-EEG study on the effects of benzodiazepine and zopiclone in schizophrenic patients

Polysomnographic examinations (PSG) were performed on 6 male schizophrenic outpatients who were being treated with benzodiazepine (BZD) hypnotics in combination with neuroleptics and 6 healthy male volunteers. In schizophrenic subjects, zopiclone (ZPC), 15 mg/day, was substituted for the BZD hypnotics, and PSGs were recorded again during ZPC therapy. All-night sleep stage scoring was carried out by visual analysis, and computerized period-amplitude analysis of sleep EEG was also performed. The schizophrenics showed marked reduction in the amount of slow-wave sleep (SWS) and in the number of delta half-waves during all-night sleep, especially those with higher amplitude, as compared to the normals. The number of delta half-waves in the patients was markedly reduced during the first sleep cycle. The average amplitude of delta half-waves during all-night sleep in the schizophrenics was significantly lower than that in the normals. The half-wave count of total delta waves in the schizophrenics was higher during treatment with ZPC than with BZDs, although no significant differences were observed in the amount of SWS between the two treatments. Soundness of sleep in the subjective sleep assessment was better evaluated during treatment with ZPC than BZDs. These results suggest that reduction of SWS in schizophrenia may be attributable mainly to the decrease in the number of delta waves with higher amplitude and that ZPC may induce deeper sleep in schizophrenics than BZDs.

Is schizophrenia due to excessive synaptic pruning in the prefrontal cortex? The Feinberg hypothesis revisited

Several lines of evidence support the notion that a substantial reorganization of cortical connections, involving a programmed synaptic pruning, takes place during adolescence in humans. A review of neurobiological abnormalities in schizophrenia indicates that the neurobiological parameters that undergo peripubertal regressive changes may be abnormal in this disorder. An excessive pruning of the prefrontal corticocortical, and corticosubcortical synapses, perhaps involving the excitatory glutamatergic inputs to pyramidal neurons, may underlie schizophrenia. A reciprocal failure of pruning in certain subcortical structures, such as lenticular nuclei, may also occur. Several developmental trajectories, related to early brain insults as well as genetic factors affecting postnatal neurodevelopment, could lead to the illness. These models would have heuristic value and may be consistent with several known facts of the schizophrenic illness, such as its onset in adolescence and the gender differences in its onset and natural course. The relationship between these models and other etiological models of schizophrenia are summarized and approaches to test relevant hypotheses are discussed.

A large scale, high resolution, automated system for rat sleep staging. II. Validation and application

An automated rat sleep staging system was used to describe sleep-waking behaviour in a large number of rats. The computer scorings were validated by visual analysis of a limited set of data by two human raters and the agreement varied between 82 and 100% for homogeneous segments of the different sleep-waking stages. The automated system proved to be very consistent in view of the small variation in placebo values over 110 experiments. The data show that classification of rat sleep waking behaviour into 6 different stages is both advisable and feasible. The experiments further show that rat age (over a range from 0.5 to 2 years) does not greatly affect rat sleep-waking behaviour.

Effects of age on delta and REM sleep parameters

Sleep EEGs were evaluated in 24 men without medical and psychiatric disease segregated into 3 age groups: 21-30, 31-40, and 51-70 years of age. Sleep was evaluated by 3 different methods: traditional sleep stage scoring, computer-assisted delta and rapid eye movement (REM) quantification, and power spectral analysis. Analysis of manually scored sleep variables revealed that age-related changes in sleep were most pronounced in the oldest age group (51-70). Older subjects spent more time awake, had low sleep efficiency and sleep maintenance, displayed a decreased REM latency, and spent less time in delta sleep. Computer quantification further confirmed that the largest drop in delta activity occurred between the 21-30 and the 31-40 year olds. The largest decrease in delta activity occurred to the greatest extent during the first 100 min of sleep (NREM period 1), and was characterized by a shift in the spectral distribution of power towards higher delta frequencies. Total nighttime REM was increased in the 31-40-year-old group as compared to older and younger subjects. This unexpected non-linear trend may reflect a progressive tendency toward 'lightening' of sleep with increasing age. These studies further suggest that the effects of aging should be incorporated into models aiming at explaining the physiology of sleep.

Sleep spindles in normal elderly: comparison with young adult patterns and relation to nocturnal awakening, cognitive function and brain atrophy

Visual measurements of sleep spindles were carried out in 48 elderly and 20 young normal adults. Computed tomography brain scans and psychometric testing were also performed. Earlier findings of reduced spindle abundance, amplitude and duration in the elderly were confirmed. In addition, we demonstrated a linear increase in spindle density and duration across NREMPs in young adults that was absent in the elderly, indicating that age affects the temporal pattern as well as the quantity of spindles. Contrary to what seemed a highly plausible hypothesis, the amount of waking in the elderly was not inversely correlated with spindle abundance, confirming earlier observations (Feinberg et al. 1967) but in a much larger group. This finding suggests that spindle abundance does not reflect the integrity of the systems that maintain the brain in NREM sleep. We also were unable to show any clear evidence that relative preservation of spindles in the elderly is associated with relative preservation of cognitive skills: psychometric performance and spindle measures were, in most instances, not significantly correlated. However, the test of this hypothesis was limited by the high level of function and the narrow range of impairment of these Ss. One intriguing positive finding was the significant inverse relation between ratings of sulcal atrophy and spindle amplitude. This observation suggests an etiology for the reduced amplitude of the sleep EEG in old age. This change is one of the most striking effects of age on brain electrophysiology.

Log amplitude is a linear function of log frequency in NREM sleep eeg of young and elderly normal subjects

The log of the amplitude of EEG waves during NREM sleep is a linear function of the log of their frequency. The slope of this function is reliable within individuals, is significantly less steep in elderly than in young subjects and, in both groups, becomes flatter across successive NREM periods. We interpret these results as consistent with the hypothesis that the function of NREM sleep is to reverse the effects of waking on the brain. According to this model the decreased steepness of slope in the elderly and in later NREM periods reflects the diminishing intensity of these processes. Whatever the correct interpretation, the within-subject consistency of slope values permits their empirical study as a function of experimental manipulations. In addition, the quantitative F-A function established here (A = c/Fb) sets constraints that may prove useful for physiologic models of EEG waves during sleep.

Are there permanent effects of night shift work on sleep?

The sleep structures, patterns and subjective evaluations of 50-60 year old nurses with varying amounts of night shift experience during their nursing careers were compared with the sleep of 50-60 year old females without night shift experience. Seven nurses had extensive prior night shift experience and were currently on night shift schedules, seven nurses had extensive night shift experience but were on current day schedules, five nurses, currently on day schedules, had had limited night shift experience. There were limited differences between the nurses on current day schedules and the non shift women. The current night shift scheduled nurses showed characteristic displaced sleep responses. It was concluded that there is little support for an hypothesis of a permanent effect of night shift work experience on subsequent sleep.

The measurement and characteristics of sleep in older persons

Measures of the sleep structure, patterns and evaluative responses of 40 males and 40 females between the ages of 50-60 years are presented. Measurement methodology is emphasized. The inability to sustain sleep is clearly indexed by the sleep structure measures. These tendencies are greater in the males. The absolute diminution of slow wave sleep is questioned. Sleep pattern measures show wide inter and intra subject variability with few sex differences. Three fourths of the subjects reported naps in a two week period and men report more frequent but shorter naps. The subjective measures have limited concurrent relations to EEG measures and constitute a complex multifaceted content domain. The overall picture is of a system in change characterized by a wide range of individual differences.

Disturbances of sleep and cognitive functioning in patients with dementia

The relationship of sleep, circadian rhythms, and cognitive impairment in dementia patients is briefly reviewed. All-night sleep EEG data were collected in relatively young and relatively unimpaired patients with presumptive Alzheimer's disease and eight age-matched controls. Delta sleep time and Delta sleep % (Stages 3 and 4)--but not REM sleep measures--were significantly reduced in the patients. Implications of these findings are discussed.

Unilateral dopamine deficit and lateral eeg asymmetry: sleep abnormalities in hemi-Parkinson's patients

The hypothesis was tested that unilateral dopamine deficiency leading to the contralateral extrapyramidal syndrome (hemi-parkinsonism) would cause distinctly asymmetric EEG sleep patterns. In 7 hemi-Parkinson's patients 2 nights of sleep were monitored along with pre-sleep waking periods. No medication was given prior to the first night. The second night followed at least 2 months of L-DOPA medication. Although in all patients sleep architecture was disturbed, no statistically significant asymmetries of sleep patterns were obtained. L-DOPA medication improved the quality of sleep. Delta sleep was most visibly improved. Also, post-treatment enhancement of the mean delta power over the parkinsonian hemisphere was supported statistically. The role of dopamine in slow wave sleep control and mechanisms of contralateral hemisphere involvement are discussed.

[Realization of a system which permits automatic analysis of sleep of infants (2-12 months)]

We have developed a system which permits automatic analysis of sleep of infants from 2 to 12 months of age. It is based on the calculation of a score on the basis of 6 parameters weighted according to their importance in determining the different phases of sleep. We use 3 EEG parameters derived from spectral analysis of the Cz-Oz derivation: total spectral energy (Hjorth activity), energy of the delta band, and energy of the beta band, and 3 polygraphic parameters: variability of muscle activity in each minute, variability of the respiratory frequency and presence or absence of rapid eye movements. The analysis provides a list of the sleep phases, minute by minute, and a traditional sleep diagram; we also calculate the successive appearances of the different sleep phases, in 10 min periods, and schematize these results in a diagram which shows the general trend of each sleep phase during the night. When compared with visual analysis, these results are satisfactory, since we observe on average 86.2% agreement in the differentiation of calm, paradoxical and transitional sleep, and 76.4% agreement in the differentiation of stages II, III and IV of calm sleep.

The sleep of older subjects fifteen years later

The EEG sleep of 5 subjects originally recorded in their early 50s was recorded 15 yr. later in their mid-60s. Increased within-sleep awakenings were present and shorter sleep stages. A modified slow wave scoring system resulted in an increased amount rather than the previously established decline in slow wave sleep with aging. Interpretive cautions necessary in extended-time studies are noted. Reliability of awakening measures across time was seen.

Sleep stage responses of older and younger subjects after sleep deprivation

EEG sleep stage measures were obtained on younger subjects (18-22 years) and older subjects (40-50 years) at 9 a.m. after 2 nights of sleep loss. The first 200 min were compared. Both groups displayed sharply reduced latencies and increased stage 4 sleep. The proportionate distribution of stage amounts and numbers was not different. However, the younger group entered slow wave sleep more quickly.

Age-related changes in sleep in depressed and normal subjects

All-night electroencephalographic (EEG) sleep data were examined a function of age in normal control subjects and hospitalized, unmedicated depressed patients with primary affective illness. By analysis of variance, Total Sleep time, Delta Sleep, Sleep Efficiency, Rapid Eye Movement (REM) Sleep, and REM Latency decreased as a function of age, whereas Early Morning Awake time and Intermittent Awake time increased. Compared with normal controls, after the effects of age were covaried out, depressed patients had a greater Sleep Latency, Early Morning Awake time, Intermittent Awake time, Duration and REM Density of the first REM period, and average REM Density for the night, as well as less Sleep Efficiency, less Delta Sleep, and shorter REM Latency, Early Morning Awake time increased with age in depressives but not in normals.

The relationship of alpha and delta EEG frequencies to pain and mood in 'fibrositis' patients treated with chlorpromazine and L-tryptophan

Aspects of sleep stage evaluation and analysis of alpha and delta EEG frequencies in sleep were shown to be related to musculo-skeletal pain and mood disturbance in patients with 'fibrositis syndrome'. Patients were treated at bedtime for 3 weeks with either chlorpromazine, 100 mg (8 patients), or L-tryptophan, 5 g (7 patients). Chlorpromazine, but not L-tryptophan, was associated with increased slow wave sleep and amelioration of pain and mood symptoms. Mean percent time/min or mean percent power/min of alpha frequency during NREM and REM sleep corrlated with overnight increase in pain measures, hostility, and decrease in energy. On the other hand, mean percent time/min of delta in NREM sleep was related to overnight decrease in pain and mean percent delta power/min was associated with decreased anxiety and hostility, and increased energy.