Increased homeostatic response to behavioral sleep fragmentation in morning types compared to evening types

STUDY OBJECTIVES: To evaluate the influence of chronotype on sleep stages and quantitative sleep EEG when sleep pressure is increased and sleep schedule remains constant. DESIGN: A 5-day session comprising an adaptation night, a baseline night, two nights of sleep fragmentation, and a recovery night. SETTING: Chronobiology laboratory. PARTICIPANTS: Twenty-four healthy subjects aged 19-34 years: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women with a habitual sleep duration of 7 to 9 hours. Interventions: Two nights of behavioral sleep fragmentation induced by forced 5-min awakenings every half-hour. MEASUREMENTS AND RESULTS: Each night of polysomnography recording lasted 8 hours and was based on each subject's preferred sleep schedule. On both nights of sleep fragmentation, stage 1 sleep increased, while both total sleep time and minutes of slow wave sleep decreased. No difference was observed in sleep architecture between morning types and evening types during sleep fragmentation nights or during recovery night. Spectral analysis of all-night NREM sleep EEG showed that during the recovery night, morning types had a larger fronto-central increase in low frequency activities and a larger centro-parietal decrease in 14-15 Hz activity than evening types. The largest group difference was for slow wave activity in the fronto-central area during the first part of the sleep episode. CONCLUSIONS: These results add further support to a postulated difference in homeostatic sleep regulation between morning types and evening types, with morning types showing indications of a higher homeostatic response to sleep disruption.     

Motor sequence learning increases sleep spindles and fast frequencies in post-training sleep

STUDY OBJECTIVES: To investigate polysomnographic (PSG) sleep and NREM sleep characteristics, including sleep spindles and spectral activity involved in offline consolidation of a motor sequence learning task. DESIGN: Counterbalanced within-subject design. SETTING: Three weekly visits to the sleep laboratory. PARTICIPANTS: Fourteen healthy participants aged between 20 and 30 years (8 women). INTERVENTIONS: Motor sequence learning (MSL) task or motor control (CTRL) task before sleep. MEASUREMENTS AND RESULTS: Subjects were trained on either the MSL or CTRL task in the evening and retested 12 hours later the following morning on the same task after a night of PSG sleep recording. Total number and duration of sleep spindles and spectral power between 0.5 and 24 Hz were quantified during NREM sleep. After performing the MSL task, subjects exhibited a large increase in number and duration of sleep spindles compared to after the CTRL task. Higher sigma (sigma; 13 Hz) and beta (beta; 18-20 Hz) spectral power during the post-training night's sleep were also observed after the MSL task. CONCLUSIONS: These results provide evidence that sleep spindles are involved in the offline consolidation of a new sequence of finger movements known to be sleep dependent. Moreover, they expand on prior findings by showing that changes in NREM sleep following motor learning are specific to consolidation (and learning), and not to nonspecific motor activity. Finally, these data demonstrate, for the first time, higher fast rhythms (beta frequencies) during sleep after motor learning.     

Circadian and homeostatic sleep regulation in morningness-eveningness

Morningness-eveningness has been associated with the entrained circadian phase. However, we recently identified morning and evening types having similar circadian phases. In this paper, we compared parameters of slow-wave activity (SWA) decay in non-rapid-eye-movement (NREM) sleep between these two subgroups to test the hypothesis that differences in the dynamics of nocturnal homeostatic sleep pressure could explain differences in sleep timing preference. Twelve morning-type subjects and 12 evening-type subjects with evening types (aged 19-34 years) selected using the Morningness-Eveningness Questionnaire were further classified according to the phase of their dim light melatonin onset (DLMO). The six morning types with the earliest DLMO were compared to the six evening types with the latest DLMO ('extreme' phases), and the six morning types with the latest DLMO were compared to the six evening types with the earliest DLMO ('intermediate' phases). Subjects slept according to their preferred sleep schedule. Spectral activity in four midline derivations (Fz, Cz, Pz, Oz) was calculated in NREM sleep and an exponential decay function was applied on SWA data averaged per sleep cycle. In the subjects with intermediate circadian phases, both initial level and decay rate of SWA in Fz were significantly higher in morning than in evening types. No difference appeared between chronotypes of extreme circadian phases. There was no correlation between individual estimates of SWA decay and DLMO. These results support the hypothesis that chronotype can originate from differences in the dissipation of sleep pressure and that homeostatic and circadian processes influence the sleep schedule preference independently.     

The night before night shift: Chronotype impacts total sleep and rapid eye movement sleep during a strategically delayed sleep

Transition to night shift may be improved by strategically delaying the main sleep preceding a first night shift. However, the effects of delayed timing on sleep may differ between chronotypes. Therefore, the study aim was to compare the impacts of chronotype on sleep quality and architecture during a normally timed sleep opportunity and a delayed sleep opportunity. Seventy-two (36 female, 36 male) healthy adults participated in a laboratory study. Participants were provided with a normally timed sleep opportunity (23:00–08:00) and a delayed sleep opportunity (03:00–12:00) over two consecutive nights in a sleep laboratory. Sleep was monitored by polysomnography (PSG), and chronotype was determined from dim light melatonin onset (DLMO). A tertile split of DLMO defined early (20:24 ± 0:42 h), intermediate (21:31 ± 0:12 h), and late chronotype (22:56 ± 0:54 h) categories. Although there was no main effect of chronotype on any sleep measure, early chronotypes obtained less total sleep with delayed sleep than with normally timed sleep (p = 0.044). Intermediate and late chronotypes obtained more rapid eye movement (REM) sleep with delayed sleep than with normally timed sleep (p = 0.013, p = 0.012 respectively). Wake was more elevated for all chronotypes in the later hours of the delayed sleep opportunity than at the start of the sleep opportunity. Strategically delaying the main sleep preceding a first night shift appears to benefit intermediate and late chronotypes (i.e., more REM sleep), but not early chronotypes (i.e., less total sleep). Circadian processes appear to elevate wakefulness for all chronotypes in the later stages of a delayed sleep opportunity.     

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.     

Spectral analysis of the sleep electroencephalogram during adolescence

OBJECTIVES: To describe developmental changes of the human sleep electroencephalogram (EEG) during adolescence using EEG spectral analysis and specifically to compare the nocturnal dynamics of slow-wave activity (EEG spectral power 0.6-4.6 Hz, a marker for sleep homeostatic pressure) in prepubertal and mature adolescents. DESIGN: After 10 nights on a fixed 10-hour sleep schedule without daytime naps, participants were studied during a 10-hour baseline night. SETTING: Data were collected in a 4-bed sleep research laboratory. PARTICIPANTS: Eight prepubertal children (pubertal stage Tanner 1; mean age 11.3 years, SD +/- 1.2, 4 boys) and 8 mature adolescents (Tanner 5; mean age 14.1 years, +/- 1.3, 3 boys). INTERVENTIONS: Not applicable. MEASUREMENTS: All-night polysomnography was performed. Sleep stages were scored according to conventional criteria. EEG power spectra (of derivation C3/A2) were calculated using a fast Fourier transform routine. RESULTS: A reduction of non-rapid eye movement (NREM) sleep stage 4 (by 40.1%) and greater amounts of stage 2 sleep (19.7%) were found in mature compared to prepubertal adolescents. NREM sleep EEG power was lower in the frequency ranges < 7 Hz, 11.8 to 12.6 Hz, and 16.2 to 16.8 Hz in mature adolescents. A reduction of rapid eye movement sleep spectral power was present in the frequency ranges < 8.6 Hz and 9.6 to 15 Hz for mature compared to prepubertal adolescents. Slow-wave activity showed identical dynamics within individual NREM sleep episodes and across the night in both developmental groups. CONCLUSIONS: The homeostatic recuperative drive during sleep remains unchanged across puberty. The decline of slow-wave sleep during adolescence may reflect developmental changes of the brain rather than changes of sleep regulatory processes.     

The circadian and homeostatic modulation of sleep pressure during wakefulness differs between morning and evening chronotypes

The purpose of this study was to evaluate homeostatic and circadian sleep process in 'larks' and 'owls' under daily life conditions. Core body temperature, subjective sleepiness and waking electroencephalogram (EEG) theta-alpha activity (6.25-9 Hz) were assessed in 18 healthy men (nine morning and nine evening chronotypes, 21.4 +/- 1.9 years) during a 36-h constant routine that followed a week of a normal 'working' sleep-wake schedule (bedtime: 23.30 h, wake time: 07.30 h). The phase of the circadian rhythm of temperature and sleepiness occurred respectively, 1.5 h (P = 0.01) and 2 h (P = 0.009) later in evening- than in morning-type subjects. Only morning-type subjects showed a bimodal rhythm of sleep-wake propensity. The buildup of subjective sleepiness, as quantified by linear regression, was slower in evening than in morning types (P = 0.04). The time course of EEG theta-alpha activity of both chronotypes could be closely fitted by an exponential curve. The time constant of evening types was longer than that of morning types (P = 0.03), indicating a slower increase in sleep pressure during extended wakefulness. These results suggest that both the circadian signal and the kinetics of sleep pressure buildup differ between the two chronotypes even under prior naturalistic conditions mimicking the usual working day.     

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.     

Association between sleep and morning testosterone levels in older men

STUDY OBJECTIVES: The circulating testosterone levels of healthy men decline with advancing age. This process is characterized by considerable inter-individual variability, the causes of which are of significant biological and clinical interest but remain poorly understood. Since sleep quantity and quality decrease with age, and experimentally-induced sleep loss in young adults results in hormonal changes similar to those that occur spontaneously in the course of aging, this study examined whether some of the variability in circulating testosterone levels of older men can be related to objective differences in their sleep. DESIGN: Observational study. SETTING: General community and university clinical research center. PARTICIPANTS: Twelve healthy men ages 64 to 74 years. INTERVENTIONS: Three morning blood samples were pooled for the measurement of total and free testosterone. In addition to overnight laboratory polysomnography, wrist activity monitoring for 6-9 days was used to determine the amount of nighttime sleep of the participants in everyday life settings. MEASUREMENTS AND RESULTS: The main outcome measures were total sleep time and morning testosterone levels. Sleep time in the laboratory was correlated with the usual amount of nighttime sleep at home (Pearson's r = 0.842; P = 0.001). Bivariate correlation and multiple linear regression analyses revealed that the amount of nighttime sleep measured by polysomnography was an independent predictor of the morning total (Beta 0.792, P = 0.017) and free (Beta 0.741, P = 0.029) testosterone levels of the subjects. CONCLUSIONS: Objectively measured differences in the amount of nighttime sleep are associated with a significant part of the variability in the morning testosterone levels of healthy older men.     

Polysomnography and self-reported sleep, pain, fatigue, and anxiety in children with active and inactive juvenile rheumatoid arthritis

OBJECTIVE: To compare polysomnography (PSG) and self-reported sleep, symptoms (pain and fatigue), and anxiety between children with active and inactive juvenile rheumatoid arthritis (JRA) and examine relations among sleep, symptoms, and anxiety. METHODS: Two consecutive nights of PSG, self-reported sleep, and symptoms were obtained in 70 children 6-11 years of age with active (n = 35) or inactive (n = 35) JRA. RESULTS: On the second (study) night, PSG and self-reported sleep variables were not different, but pain and fatigue were significantly higher (both p <.02) in children with active compared to inactive disease. In a stepwise regression, age, medications, disease status, anxiety, evening pain, total sleep time, and arousals explained 36% of the variance in fatigue and age, disease status, and evening pain were significant (all p <.04) predictors of fatigue. All children showed longer sleep latency and reduced sleep efficiency on the first night in the laboratory. CONCLUSIONS: Sleep was not altered in children with active JRA, however, the "first night effect" suggests that valid laboratory sleep assessments require an adaptation night.     

Shift work,sleep disturbances and social jetlag in healthcare workers

The aim of this study was to compare chronotype‐ and age‐dependent sleep disturbances and social jetlag between rotating shift workers and non‐shift workers, and between different types of shifts. In the Klokwerk+ cohort study, we included 120 rotating shift workers and 74 non‐shift workers who were recruited from six Dutch hospitals. Participants wore Actigraph GT3X accelerometers for 24 hr for 7 days. From the Actigraph data, we predicted the sleep duration and social jetlag (measure of circadian misalignment). Mixed models and generalized estimation equations were used to compare the sleep parameters between shift and non‐shift workers. Within shift workers, sleep on different shifts was compared with sleep on work‐free days. Differences by chronotype and age were investigated using interaction terms. On workdays, shift workers had 3.5 times (95% confidence interval: 2.2–5.4) more often a short (< 7 hr per day) and 4.1 times (95% confidence interval: 2.5–6.8) more often a long (≥ 9 hr per day) sleep duration compared with non‐shift workers. This increased odds ratio was present in morning chronotypes, but not in evening chronotypes (interaction p‐value < .05). Older shift workers (≥ 50 years) had 7.3 times (95% confidence interval: 2.5–21.8) more often shorter sleep duration between night shifts compared with work‐free days, while this was not the case in younger shift workers (< 50 years). Social jetlag due to night shifts increased with increasing age (interaction p‐value < .05), but did not differ by chronotype (interaction p‐value ≥ .05). In conclusion, shift workers, in particular older workers and morning chronotypes, experienced more sleep disturbances than non‐shift workers. Future research should elucidate whether these sleep disturbances contribute to shift work‐related health problems.     

Interactions of time of day and sleep with between-session habituation and extinction memory in young adult males

Within-session habituation and extinction learning co-occur as do subsequent consolidation of habituation (i.e., between-session habituation) and extinction memory. We sought to determine whether, as we predicted: (1) between-session habituation is greater across a night of sleep versus a day awake; (2) time-of-day accounts for differences; (3) between-session habituation predicts consolidation of extinction memory; (4) sleep predicts between-session habituation and/or extinction memory. Participants (N = 28) completed 4–5 sessions alternating between mornings and evenings over 3 successive days (2 nights) with session 1 in either the morning (N = 13) or evening (N = 15). Twelve participants underwent laboratory polysomnography. During 4 sessions, participants completed a loud-tone habituation protocol, while skin conductance response (SCR), blink startle electromyography (EMG), heart-rate acceleration and heart-rate deceleration (HRD) were recorded. For sessions 1 and 2, between-session habituation of EMG, SCR and HRD was greater across sleep. SCR and HRD were generally lower in the morning. Between-session habituation of SCR for sessions 1 and 2 was positively related to intervening (first night) slow wave sleep. In the evening before night 2, participants also underwent fear conditioning and extinction learning phases of a second protocol. Extinction recall was tested the following morning. Extinction recall was predicted only by between-session habituation of SCR across the same night (second night) and by intervening REM. We conclude that: (1) sleep augments between-session habituation, as does morning testing; (2) extinction recall is predicted by concurrent between-session habituation; and (3) both phenomena may be influenced by sleep.     

The relation between polysomnography and subjective sleep and its dependence on age – poor sleep may become good sleep

Women complain more about sleep than men, but polysomnography (PSG) seems to suggest worse sleep in men. This raises the question of how women (or men) perceive objective (PSG) sleep. The present study sought to investigate the relation between morning subjective sleep quality and PSG variables in older and younger women. A representative sample of 251 women was analysed in age groups above and below 51.5 years (median). PSG was recorded at home during one night. Perceived poor sleep was related to short total sleep time (TST), long wake within total sleep time (WTSP), low sleep efficiency and a high number of awakenings. The older women showed lower TST and sleep efficiency and higher WTSP for a rating of good sleep than did the younger women. For these PSG variables the values for good sleep in the older group were similar to the values for poor sleep in the young group. It was concluded that women perceive different levels of sleep duration, sleep efficiency and wake after sleep onset relatively well, but that older women adjust their objective criteria for good sleep downwards. It was also concluded that age is an important factor in the relation between subjective and objective sleep.     

Sleep laboratory studies on the single-dose effects of serotonin reuptake inhibitors paroxetine and fluoxetine on human sleep and awakening qualities.

Paroxetine is a novel antidepressant drug with selective serotonin (5-HT) reuptake inhibitory properties. In a double-blind placebo-controlled crossover sleep laboratory study the single-dose effects on objective and subjective sleep and awakening qualities were investigated after paroxetine 20, 30 and 40 mg morning doses (PX 20, 30, 40), paroxetine 30 mg evening dose, fluoxetine 40 mg morning dose (FX 40) and placebo in 18 healthy young volunteers. The drugs were orally administered in 2-wk intervals. In addition to each drug night, the adaptation night and washout night were recorded. Polysomnographic investigations (10:30 p.m. to 6:00 a.m.) showed a delayed sleep onset only after the morning intake of paroxetine, PX 40 being statistically different from placebo. Total sleep time and sleep efficiency deteriorated under morning PX 30, PX 40 and evening PX 30 as compared to placebo. The nocturnal wake time and sleep stage 1 increased under the paroxetine. Rapid eye movement (REM) reduction (min and %) occurred dose dependently after all paroxetine doses, but the REM latency was lengthened only after the morning intake. The suppressant effect on REM sleep is characteristic for antidepressants and was still significant in the washout nights following PX 40 and evening PX 30. The only statistically relevant finding under 40 mg fluoxetine referred to the increase of REM latency in both drug and washout nights. In contrast to objective results, subjective sleep quality remained generally unchanged. Attention, concentration and reaction performance improved under paroxetine as compared to baseline. The deterioration of well-being under PX 40 might be related to the appearance of drowsiness and nausea. Blood pressure and pulse rate were unaffected.     

Morning or evening activity improves neuropsychological performance and subjective sleep quality in older adults

STUDY OBJECTIVES: Sleep disturbances and decline in neuropsychological performance are common in older adults. Reduced social and physical activity is likely a contributing factor for these age-related changes in sleep and cognition. We previously demonstrated that a program of structured social and physical activity, with 2 daily activity sessions, 1 in the morning and 1 in the evening for a relatively short period of 2 weeks, improved sleep and neuropsychological performance in community-dwelling older adults. The goals of this pilot study were to determine whether a single daily morning or evening activity session for 2 weeks would also improve sleep and neuropsychological function and whether these effects were dependent on the timing of the activity sessions. DESIGN: We compared the effect of morning or evening structured activity sessions in a repeated-measures crossover design. Subjective mood, neuropsychological performance tasks, and subjective and objective measures of sleep were assessed at baseline and after the intervention. SETTING: All procedures took place in the participant's residence. PARTICIPANTS: Twelve older men and women (74.6 +/- 5.5 years of age). INTERVENTIONS: Subjects participated in 14 days of structured activity sessions in the morning (9:00-10:30 am) or evening (7:00-8:30 pm). Sessions consisted of stretching, low-impact aerobics, and game playing. MEASUREMENTS AND RESULTS: Exposure to either morning or evening activity significantly improved performance on a neuropsychological test battery. Morning activity sessions increased throughput on 4 of 8 performance tasks, while evening activity sessions improved throughput on 7 of the 8 performance tasks. Subjective sleep-quality ratings, measured by the Pittsburg Sleep Quality Index, improved following activity sessions in either the morning or the evening. Objective measures of sleep did not improve when measured by actigraphy or polysomnography. CONCLUSIONS: These results suggest that short-term exposure to either morning or evening social and physical activity improves objective measures of neuropsychological performance and subjective sleep quality in the elderly. Increasing exposure to social and physical activity may be a useful intervention to improve sleep quality and daytime function in older adults.     

Sex differences in brain oscillatory activity during sleep and wakefulness in obstructive sleep apnea

Epidemiological studies consistently show a male predominance in obstructive sleep apnea (OSA). Hormonal differences, breathing control, upper airway anatomy and fat distribution have been proposed as causes of gender differences in OSA. Clinical manifestations are accentuated in men, although white matter structural integrity is affected in women. To the best of our knowledge, no previous studies have explored gender differences in the electrical brain activity features of OSA. Polysomnography was performed on 43 patients with untreated OSA (21 women, 22 men), and power spectral density (1–50 Hz) was compared between groups across sleep and wakefulness at two levels of OSA severity. Severe versus moderate OSA showed decreased power for fast frequencies (25–29 Hz) during wakefulness. OSA men displayed decreased power of a large frequency range (sigma, beta and gamma) during sleep compared with women. Comparisons of men with severe versus moderate OSA presented significantly decreased sigma power during non‐rapid eye movement (NREM) sleep, but significantly increased delta activity during REM sleep. Meanwhile, women with severe versus moderate OSA showed no significant power differences in any condition. These findings indicated a different evolution of brain oscillations between OSA men and women with significant impairment of brain activity related to cognitive processes. Our study emphasizes the importance of understanding the differential effects of sleep disorders on men and women in order to develop more precise diagnostic criteria according to gender, including quantitative electroencephalogram (EEG) analysis tools.     

Toddler behavior following polysomnography: effects of unintended sleep disturbance

STUDY OBJECTIVES: Childhood sleep disorders are consistently shown to affect behavior and cognition, but first-night effects on these measures are generally unknown. We sought to examine how sleep in the home versus the laboratory differed among healthy toddlers and how such differences relate to standardized scores on assessments the morning following polysomnography. DESIGN, SETTING, AND PARTICIPANTS: Twenty healthy 14-month-olds wore actigraphs during nighttime sleep at home for 5 nights preceding and during standard overnight laboratory polysomnography. The Bayley Scales of Infant Development (BSID-II) were administered once the morning after polysomnography. MEASUREMENTS AND RESULTS: All subjects had normal polysomnography. Sleep-start times at home and during polysomnography did not differ, whereas, during polysomnography, subjects awoke earlier (p = .008, d = .58), their total sleep time (p <. 001, d = 1.1) and sleep efficiency (p = .004, d = .57) were reduced, and they had shorter sleep-bout lengths (p = .004, d = .03), less immobility (p = .003, d = .62), and greater average activity during sleep (p <. 001, d = .98). Standardized assessments were not affected by differences between home and polysomnography night sleep, but children with greater emotional regulation difficulty had a lower percentage of immobility (r = -0.67, p = .001) and increased sleep fragmentation (r = -0.60, p = .005) during polysomnography. CONCLUSIONS: Although sleep-onset times were preserved, sleep in the laboratory was disrupted, compared with at home. These differences did not affect standardized scores, but the magnitude of the difference was associated with worse emotional regulation. The effects of sleep disturbance during polysomnography, or the influence of poor emotional regulation on sleep in the laboratory, should be considered in studies of young children.     

Phosphorous31 magnetic resonance spectroscopy after total sleep deprivation in healthy adult men

STUDY OBJECTIVES: To investigate chemical changes in the brains of healthy adults after sleep deprivation and recovery sleep, using phosphorous magnetic resonance spectroscopy. DESIGN: Three consecutive nights (baseline, sleep deprivation, recovery) were spent in the laboratory. Objective sleep measures were assessed on the baseline and recovery nights using polysomnography. Phosphorous magnetic resonance spectroscopy scans took place beginning at 7 am to 8 am on the morning after each of the 3 nights. SETTING: Sleep laboratory in a private psychiatric teaching hospital. PARTICIPANTS: Eleven healthy young men. INTERVENTIONS: Following a baseline night of sleep, subjects underwent a night of total sleep deprivation, which involved supervision to ensure the absence of sleep but was not polysomnographically monitored. MEASUREMENTS AND RESULTS: No significant changes in any measure of brain chemistry were observed the morning after a night of total sleep deprivation. However, after the recovery night, significant increases in total and beta-nucleoside triphosphate and decreases in phospholipid catabolism, measured by an increase in the concentration of glycerylphosphorylcholine, were observed. Chemical changes paralleled some changes in objective sleep measures. CONCLUSIONS: Significant chemical changes in the brain were observed following recovery sleep after 1 night of total sleep deprivation. The specific process underlying these changes is unclear due to the large brain region sampled in this exploratory study, but changes may reflect sleep inertia or some aspect of the homeostatic sleep mechanism that underlies the depletion and restoration of sleep. Phosphorous magnetic resonance spectroscopy is a technique that may be of value in further exploration of such sleep-wake functions.     

The effects of age and gender on sleep EEG power spectral density in the middle years of life (ages 20-60 years old)

The effects of age and gender on sleep EEG power spectral density were assessed in a group of 100 subjects aged 20 to 60 years. We propose a new statistical strategy (mixed-model using fixed-knot regression splines) to analyze quantitative EEG measures. The effect of gender varied according to frequency, but no interactions emerged between age and gender, suggesting that the aging process does not differentially influence men and women. Women had higher power density than men in delta, theta, low alpha, and high spindle frequency range. The effect of age varied according to frequency and across the night. The decrease in power with age was not restricted to slow-wave activity, but also included theta and sigma activity. With increasing age, the attenuation over the night in power density between 1.25 and 8.00 Hz diminished, and the rise in power between 12.25 and 14.00 Hz across the night decreased. Increasing age was associated with higher power in the beta range. These results suggest that increasing age may be related to an attenuation of homeostatic sleep pressure and to an increase in cortical activation during sleep.