Chronotype and sex effects on sleep architecture and quantitative sleep EEG in healthy young adults

STUDY OBJECTIVES: To evaluate the influence of chronotype (morning types and evening types) on sleep stages and quantitative sleep electroencephalograms when constraints on the sleep schedule are minimal and when sex difference is taken into account. DESIGN: A 48-hour session in the laboratory, including 2 nights of polysomnography, preceded by 7 days of ambulatory actigraphy. SETTING: Chronobiology laboratory. PARTICIPANTS: Twenty-four healthy young subjects: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: A polysomnography night of 8 hours in duration was recorded according to preferred sleep schedule. Sleep-stage analysis revealed that morning types and evening types did not differ in sleep architecture. However, morning-type men showed a higher percentage of stage 1 sleep and lower sleep efficiency than evening-type men. Electroencephalogram spectral analysis was conducted in non-rapid eye movement sleep for 6 frequency bands. Morning types had more spectral power in low sigma (12-14 Hz) compared with evening types. The most robust difference between women and men was found in high sigma (14-16 Hz) and was not present between chronotypes. The decay rate of slow-wave activity (1-5 Hz) tended to be faster in morning types compared with evening types (P = .06). This rate was almost identical for women and men. CONCLUSIONS: These results agree with the hypothesis that homeostatic sleep regulation differs between morning types and evening types, with morning types showing indications of a higher rate of dissipation of sleep pressure during the night. Morningness-eveningness seems to affect sleep in a sex-specific manner, with men being more affected by their chronotype.     

Sleep structure and EEG power density in morning types and evening types during a simulated day and night shift

The objective of this study was to examine circadian and homeostatic regulation of sleep in humans. In 8 morning types (M-types) and in 8 evening types (E-types), sleep was recorded during 3 successive nights and, after shifting sleep to the daytime, during 3 consecutive days. Night sleep was highly similar in the M-types and E-types. Day sleep clearly differed from night sleep in both types: Day sleep was shorter and had a longer first REMS episode. Furthermore, EEG power density recorded during non-REMS in the delta and theta frequency bands was higher during all day-sleep periods. Remarkably, the enhancements did not occur in non-REMS episode 1 but were delayed. This was interpreted as an inhibition of EEG power density at the beginning of sleep, possibly caused by the time course of body temperature and/or by the higher REMS propensity. Also, clear differences between the types became apparent: Only in the E-types, the non-REMS episodes shortened in response to the shift in bedtime, and probably related to this, the time course of EEG power density over consecutive non-REMS episodes became almost flat. It was concluded that the circadian system exerts not only an influence on sleep duration and REMS propensity, but also affects the time course of the non-REMS process.     

Sleep and body temperature in "morning" and "evening" people

Three groups of young, normal sleepers were selected as morning types (MTs), evening types (ETs), and neither types (NTs) as determined by the Horne and Ostberg questionnaire. Sleep and rectal temperatures were recorded under three conditions: baseline nights (Cond. 1), sleep on the recovery day after 1 night of sleep deprivation (Cond. 2), and sleep on the recovery night after 1 night and 1 day of sleep deprivation (Cond. 3). During Conds. 1 and 3, when sleep schedules were self-determined, sleep structure and body temperature were similar in MTs, and ETs, and NTs. During Cond. 2, however, MTs had poorer sleep, i.e., a smaller percentage of REM sleep and more awakenings, than ETs. This difference can be related to the evolution of temperature during Cond. 2; i.e., a temperature increase in the MT and NT and a decrease in the ET.     

Effect of 64 hours of sleep deprivation upon sleep in geriatric normals and insomniacs

Fifty-eight geriatric normal and chronic insomniac sleepers were screened with sleep recordings to define groups of 12 Normal (Sleep Efficiency greater than 85%) and Insomniac (Sleep Efficiency less than 80%) sleepers. All subjects then had 4 baseline sleep nights, 64 hours of total sleep loss, and 4 recovery nights. Insomniacs, had lower sleep efficiencies and less REM than Normals during baseline. Sleep efficiency was high (97%) in both groups on the first recovery night but decreased toward baseline values in both groups between the second (Normal) and fourth (Insomniac) recovery night. The groups had relatively little slow wave sleep, but had a significant increase on the first recovery night. Five Normals and one Insomniac had REM latency of less than 15 min on their first recovery night. This REM latency was found to be significantly correlated with the amount of slow wave sleep on baseline. Decreased REM latency in initial recovery sleep was interpreted as evidence of decreased pressure for slow wave sleep in aging.     

Daytime noise and subsequent night sleep in man

Summary The effects of daytime noise on recovery processes during subsequent undisturbed night sleep were studied in six healthy men (21–27 years), exposed to 80 dB (A) pink noise 8 h per day for 2 days. Sleep EEG, ECG, and respiration were recorded in the laboratory for five consecutive nights: two baseline nights, two nights following noise stimulation, and again one baseline night. Additionally questionnaire data were collected, reflecting a subjective impairment of the recovery function of sleep after noise exposure. EEG sleep data of the first post-noise night showed an increase in slow wave sleep with a simultaneous decrease in stage 2 sleep. During the second post-noise night these changes were less prominent. Three subjects additionally showed an instability in the sleep course coinciding with elevated heart and respiration rates. However, altogether the autonomic parameters were not clearly affected by the noise exposure. The findings support the assumption that strong daytime noise may interfere with subsequent sleep processes.Part of this work was presented at the Sixth European Congress of Sleep Research, Zürich, Switzerland 1982     

The impact of a 4-hour sleep delay on slow wave activity in twins discordant for chronic fatigue syndrome

OBJECTIVES: Chronic fatigue syndrome (CFS) has been associated with altered amounts of slow wave sleep, which could reflect reduced delta electroencephalograph (EEG) activity and impaired sleep regulation. To evaluate this hypothesis, we examined the response to a sleep regulatory challenge in CFS. DESIGN: The first of 3 consecutive nights of study served as laboratory adaptation. Baseline sleep was assessed on the second night. On the third night, bedtime was delayed by 4 hours, followed by recovery sleep. Total available sleep time was held constant on all nights. SETTING: A research sleep laboratory. PARTICIPANTS: 13 pairs of monozygotic twins discordant for CFS. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Power spectral analysis quantified slow wave activity (SWA) in the 0.5-3.9 Hz band in successive NREM periods (stage 2, 3, or 4) on each night. To ensure comparability, analyses were restricted to the first 4 NREM periods on each night. Data were coded for NREM period and twin pair. Repeated-measures analysis of variance (ANOVA) contrasted sleep delay effects across NREM periods between twin pairs. A second ANOVA calculated the SWA in each NREM period in recovery sleep relative to baseline SWA. The 2 groups of twins were similar on baseline SWA power. After sleep delay, CFS twins exhibited significantly less SWA power in the first NREM period of recovery sleep and accumulated a smaller percentage of SWA in the first NREM period than their co-twins. CONCLUSIONS: CFS is associated with a blunted SWA response to sleep challenge, suggesting that the basic sleep drive and homeostatic response are impaired.     

Increased production of evoked and spontaneous K-complexes following a night of fragmented sleep

STUDY OBJECTIVES: To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. DESIGN: 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. SETTING: The sleep research laboratory at the University of Melbourne. PARTICIPANTS: Six young healthy subjects (3 female). INTERVENTIONS: 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. MEASUREMENTS AND RESULTS: 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. CONCLUSIONS: 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.     

Twenty-four-hour structure of sleepiness in morning and evening persons investigated by ultrashort sleep-wake cycle

"Morning" and "evening" persons, defined according to a modified version of the Horne and Ostberg questionnaire, performed the 7/13 min sleep-waking schedule under attempting sleep condition after sleeping for one night in the laboratory, and under the resisting sleep condition after one night of sleep deprivation. Morning types slept significantly more under the attempting sleep condition and showed an earlier rise in nocturnal sleepiness. After sleep deprivation, morning types had a more distinct sleep propensity pattern with well-defined midafternoon and nocturnal sleep gates. In this condition there was a significant interaction between type and time of day with respect to amount of sleep: morning types slept more during the night, and evening types slept more during the day. Based on their amounts of sleep, subjects were also divided into "sleepy" and "alert" types, which were independent from the chronotypology.     

Differential effects of permanent and rotating shifts on self-report sleep length: a meta-analytic review

STUDY OBJECTIVES: The current study used the meta-analytic technique to quantitatively assess the effects of permanent and rotating shift-work schedules on sleep length. DESIGN: A meta-analysis was completed on 36 primary studies resulting in 165 effect sizes. Effect sizes comparing shift-workers to a permanent day shift control group were calculated for permanent evening shifts, permanent night shifts, and morning, evening, and night shifts worked as part of slowly and rapidly rotating shift systems. SETTING: NA PATIENTS OR PARTICIPANTS: NA INTERVENTIONS: NA RESULTS: Permanent night shifts resulted in a decrease, whereas permanent evening shifts resulted in an increase in sleep length. The shifts within rotating schedules followed the same pattern, with the addition of morning shifts having a moderate detrimental effect on sleep length. Furthermore, the speed of shift rotation had an impact. Slowly rotating shifts, in general, had the least detrimental effect on sleep length of the permanent and rotating shift-work schedules studied here. The pattern of effects among morning, evening, and night shifts was the same for rapidly and slowly rotating shifts, with night shifts having the greatest detrimental effect, morning shifts having a moderate detrimental effect and evening shifts having a positive effect on sleep length. In addition, nights on rotating shifts had a greater negative effect on sleep length than permanent night shifts. CONCLUSIONS: Slowly rotating shifts have the least negative impact on sleep length of shift-work schedules including a night shift. However, permanent night shifts could be an alternative shift-work schedule in operational settings that require many workers at night.     

The effect of clustered versus regular sleep fragmentation on daytime function

Previously, we found that regular sleep fragmentation, similar to that found in patients with sleep apnoea/hypopnoea syndrome (SAHS), impairs daytime function. Apnoeas and hypopnoeas occur in groups in patients with REM or posture related SAHS. Thus, we hypothesised that clustered sleep fragmentation would have a similar impact on daytime function as regular sleep fragmentation. We studied 16 subjects over two pairs of 2 nights and 2 days. The first night of each pair was for acclimatisation. On the second night, subjects either had their sleep fragmented regularly every 90 s, or fragmented every 30 s for 30 min every 90 min, the remaining 60 min being undisturbed. We fragmented sleep with tones to produce a minimum 3 s increase in EEG frequency. During the days following each pair of nights we tested subjects daytime function. Total sleep time (TST) and microarousal frequency were similar no both study nights. We found significantly less stage 2 (55 SD 4, 62 +/- 7%; P = 0.001) and more slow wave sleep (21 SD 3, 12 +/- 6%; P < 0.001) on the clustered night. Mean sleep onset latency was similar on MSLT (clustered 10 SD 5, regular 9 +/- 4 min; P = 0.7) and MWT (clustered 32 SD 7, regular 30 +/- 7 min; P = 0.2). There was no difference in subjects mood or cognitive function after either study night. These results suggest that although there is more slow wave sleep (SWS) on the clustered night, similar numbers of sleep fragmenting events produced similar daytime function whether the events were evenly spaced or clustered.     

Passive body heating and sleep: influence of proximity to sleep

Previous studies have found enhanced delta sleep following body heating. This study assessed the influence of body heating as a function of its proximity to sleep. Electroencephalogram (EEG) sleep patterns were compared following body heating (1 h immersion in water at 41 degrees C) at each of four times of day: morning (MO), afternoon (AF), early evening (EE), and late evening (LE), ending just prior to sleep. A delta filter/integrator system provided objective measures of delta content. Relative to baseline nights, whole-night delta sleep was increased by the two evening heating sessions only, particularly LE heating. Following LE, the increased delta occurred primarily in the first sleep cycle, whereas EE heating elicited increased delta distributed across the later sleep cycles (cycles 2-4). Effects on manually staged indices of slow wave sleep (SWS) were confined to increases in Stage 4 in the first sleep cycle following LE heating. Heating just prior to sleep also resulted in a substantial reduction in the duration of the first rapid eye movement sleep period. Sleep onset time was reduced by heating, particularly EE heating. The results indicate that body heating induces temporary changes that affect sleep propensity and both the quantity and temporal distribution of delta activity in the sleep EEG.     

Lower excitability of the corticospinal tract to transcranial magnetic stimulation during lengthening contractions in human elbow flexors

Dynamics of electroencephalographic (EEG) slow wave activity (0.5-4.5 Hz) and body temperature, as estimates, respectively, of the process S and process C, regulating sleep and waking alternate occurrence, were measured during monophasic and biphasic sleep patterns that occurred spontaneously in a 35-year-old woman who lived for 105 days in a winter-type photoperiod (10-14 h light-dark). In monophasic nights, rate of EEG synchronization showed a decreasing trend across the first three non-rapid eye movement (NREM) periods. In biphasic nights, rate of EEG synchronization increased during the third NREM period which precedes the nocturnal awakening. Temperature cycle was not different between biphasic and monophasic nights. Those results confirm that EEG dynamics reflects homeostatic sleep regulatory mechanism, and suggest that the period of prolonged wakefulness in the middle of biphasic night is pre-programmed.     

CNS arousal and neurobehavioral performance in a short-term sleep restriction paradigm

Few studies have investigated waking electrophysiological measures of arousal during sleep restriction. This study examined electroencephalogram (EEG) activity and performance during a 96-hour laboratory protocol where participants slept a baseline night (8 h), were randomly assigned to 3-, 5-, or 8-hour sleep groups for the next two nights sleep restriction (SR1, SR2), and then slept a recovery night (8 h). There were dose-dependent deficits on measures of mood, sleepiness, and reaction time that were apparent during this short-term bout of sleep restriction. The ratio of alpha to theta EEG recorded at rest indicated dose-dependent changes in CNS arousal. At 9:00 hours, both the 3- and 5-hour groups showed EEG slowing (sleepiness) during restriction, with the 3-hour group exhibiting greater deficits. Later in the day at 13:00 hours, the 5-hour group no longer exhibited EEG slowing, but the extent of slowing was more widespread across the scalp for the 3-hour group. High-frequency EEG, a measure of effort, was greater on the mornings following sleep restriction. The 5-hour group had increased beta EEG at central-parietal sites following both nights of restriction, whereas the 3-hour group had increased beta and gamma EEG at occipital regions following the first night only. Short-term sleep restriction leads to deficits in performance as well as EEG slowing that correspond to the amount and duration of sleep loss. High-frequency EEG may be a marker of effort or compensation.     

Effects of different sleep duration on delta sleep in recovery nights

The study assessed the effects of different amounts of sleep restriction on slow wave sleep (SWS) in the ensuing recovery nights. After one adaptation night and an 8-hr baseline night, six healthy men were individually studied during and following five nights in which sleep was reduced to 5, 4, 3, 2, and 1 hr with a 1-week interval between conditions. Bach sleep reduction was followed by an 8-hr recovery night. Finally, a second 8-hr baseline night was recorded. A trend analysis revealed that SWS amount in recovery nights increases with decreasing previous sleep duration. Regression analyses showed that, within each participant, the rebound of SWS after a sleep reduction is predicted better by the total duration of sleep than by the specific amount of SWS lost.     

Sleepiness/alertness on a simulated night shift following sleep at home with triazolam

Physiological sleep tendency during a simulated night shift schedule was examined in 15 middle-aged subjects following daytime sleep after administration of triazolam or placebo. A double-blind, counterbalanced, crossover design involving two tours of five laboratory nights and four daytime home sleep periods was used. Triazolam lengthened daytime sleep as measured by wrist actigraph and improved nighttime alertness as measured by the MSLT. Sleepiness was most profound during the early morning hours (0430 to 0630) but improved significantly across nights for both conditions. Repeated test of sustained wakefulness latencies and simulated assembly line task performance decreased slightly across the night, but there were no significant condition effects. Subjective data tended to support objective measures, although Stanford Sleepiness Scale ratings indicated that subjects did not perceive improved alertness at night after triazolam-aided daytime sleep.     

Selective slow-wave sleep deprivation and time-of-night effects on cognitive performance upon awakening

We evaluated the effects of selective slow-wave sleep (SWS) deprivation and time-of-night factors on cognitive performance upon awakening. Ten normal men slept for 6 consecutive nights in the laboratory: 1 adaptation, 2 baseline, 2 selective SWS deprivation, and 1 recovery night. Cognitive performance was assessed by means of a Descending Subtraction Task after 2, 5, and 7.5 h of sleep. There was an almost complete selective SWS suppression during both deprivation nights, and a significant SWS rebound during the recovery sleep. Regarding cognitive performance, a progressive linear decrease of sleep inertia upon successive awakenings was found during all experimental nights except for the recovery night. In addition, a significant decrease of sleep inertia was observed upon the morning awakening of the second deprivation night for the measure of performance speed, and a significant increase of sleep inertia upon the morning awakening of the recovery night for the measure of performance accuracy. The results show that cognitive performance upon awakening is adversely affected by sleep depth and that, during the sleep-wake transition, cognitive performance accuracy is more impaired than performance speed.     

Subjective sleepiness and physiological sleep tendency in healthy young morning and evening subjects

SUMMARY  The Multiple Sleep Latency Test (MSLT) was performed twice after 8h and after 4h of night sleep in 15 healthy young subjects (mean age: 23 y). Seven subjects could be regarded as morning, 8 subjects as evening types. After 8h of sleep significantly more evening types napped at 08.00 hours and at 12.00 hours. Evening types rated themselves more sleepy on an hourly administered visual analogous scale (VAS). Sleep onset latencies (SOL) decreased, and the amount of Stages 1 and 2 increased in all subjects dependent on the sleep restriction condition. No significant differences between morningness and eveningness concerning SOL and structure of nap structure could be observed. After 4 h of sleep there was a marked increase in subjectively rated sleepiness during the morning hours in both groups.     

The spinal precerebellar nuclei: calcium binding proteins and gene expression profile in the mouse

Sleep restriction is a widespread phenomenon, specifically in adolescents. This study investigated the impact of increasing sleep restriction in adolescents on cortisol levels and daytime sleepiness. Eighty-eight healthy adolescents were randomized to five sleep restriction protocols (four consecutive nights with 9, 8, 7, 6, or 5 h time in bed). Polysomnography (baseline and last experimental night) and multiple sleep latency test (day 6) data were obtained. Saliva cortisol levels were assessed half-hourly in the evening before and in the morning after the baseline and the last experimental night. Four nights of sleep restriction in healthy adolescents lead to a linear increase of objective sleepiness, but had no significant effect on evening or morning cortisol levels. The lack of detrimental effects of sleep restriction on cortisol levels might be due to compensation mechanisms during sleep.     

Yawning in morning and evening types

Yawning occurs more frequently in the early morning and in the late evening, close to sleep onset and after the awakening, and it might be linked to sleep propensity. We aimed to study yawning and its temporal distribution in morning and evening subjects who display different sleep-wake and sleepiness rhythms. Sixteen healthy young adults (8 evening-types and 8 morning-types, matched for age and gender) have been selected and instructed to keep their habitual sleep schedules and to signal every yawning occurrence for three consecutive days. Results show that evening-types yawn more frequently than morning-types, particularly during morning hours. Yawning frequency decreases across daytime in evening-types reaching its lowest level in the early evening and increases thereafter. Instead, in morning-types, yawning frequency remains quite low during daytime and increases in the evening. Moreover, both morning and evening types show a progressive increase of yawning frequency in the hours preceding sleep onset, whereas they differ after the awakening. Evening-types show a higher yawning frequency that remains quite stable in the hours following the awakening, while morning-types display a decline in yawning frequency. Our findings show that the temporal distribution of yawning frequency differs between chronotypes, supporting the hypothesis that differences in sleep-wake rhythm affect yawning, which could represent a behavioural sign of sleep propensity.     

Sleep deprivation suppresses the increase of rapid eye movement density across sleep cycles

We investigated the association between rapid eye movement (REM) density (REMd) and electroencephalogram (EEG) activity during non‐rapid eye movement (NREM) and REM sleep, within the re‐assessment, in a large sample of normal subjects, of the reduction of oculomotor activity in REM sleep after total sleep deprivation (SD). Coherently with the hypothesis of a role of homeostatic sleep pressure in influencing REMd, a negative correlation between changes in REMd and slow‐wave activity (SWA) was expected. A further aim of the study was to evaluate if the decreased REMd after SD affects ultradian changes across sleep periods. Fifty normal subjects (29 male and 21 female; mean age = 24.3 ± 2.2 years) were studied for four consecutive days and nights. Sleep recordings were scheduled in the first (adaptation), second (baseline) and fourth night (recovery). After awakening from baseline sleep, a protocol of 40 h SD started at 10:00 hours. Polysomnographic measures, REMd and quantitative EEG activity during NREM and REM sleep of baseline and recovery nights were compared. We found a clear reduction of REMd in the recovery after SD, due to the lack of REMd changes across cycles. Oculomotor changes positively correlated with a decreased power in a specific range of fast sigma activity (14.75–15.25 Hz) in NREM, but not with SWA. REMd changes were also related to EEG power in the 12.75–13.00 Hz range in REM sleep. The present results confirm the oculomotor depression after SD, clarifying that it is explained by the lack of changes in REMd across sleep cycles. The depression of REMd can not simply be related to homeostatic mechanisms, as REMd changes were associated with EEG power changes in a specific range of spindle frequency activity, but not with SWA.