Showing papers in "Journal of Sleep Research in 1998"

Memory consolidation during sleep: a neurophysiological perspective

Abstract: In the awake brain, information about the external world reaches the hippocampus via the entorhinal cortex, whereas during sleep the direction of information flow is reversed: population bursts initiated in the hippocampus invade the neocortex. We suggest that neocortico-hippocampal transfer of information and the modification process in neocortical circuitries by the hippocampal output take place in a temporally discontinuous manner associated with theta/gamma oscillations. On the other hand, transfer of the stored representations to neocortical areas is carried by discrete quanta of cooperative neuronal bursts (called sharp wave bursts) initiated in the hippocampus during slow wave sleep. The spatio-temporal participation of principal cells in sharp waves is determined by experience-induced changes in the CA3 recurrent collateral matrix. The co-operative, converging pre-synaptic activity can induce localized fast spikes and associated calcium influx in the apical dendrites of CA1 pyramidal cells, a necessary condition for the induction of synaptic plasticity. In addition, the subcortical effects of hippocampal sharp wave bursts may be critical in the release of various hormones which, in turn, may affect synaptic plasticity. These observations suggest that sleep patterns in the limbic system are essential for the preservation of experience-induced synaptic modifications.

Sleep loss impairs short and novel language tasks having a prefrontal focus

Abstract: Most cognitive tests administered during sleep loss are well rehearsed to remove practice effects. This can introduce tedium and a loss of novelty, which may be the key to the test's subsequent sensitivity to sleep loss, and why it may need only a few minutes administration before sleep loss effects are apparent. There is little evidence to show that any of these tests are actually affected by sleep loss if given de novo, without practice, but using a non-sleep deprived control group. Although the sleep deprivation literature advocates that short, novel and stimulating tests would not be expected to be sensitive to sleep loss, recent sleep loss findings using neuropsychological tests focussing on the prefrontal cortex, indicate that such tests may challenge this maxim. Twenty healthy young adults were randomly assigned to two groups: nil sleep deprivation (control), and 36h continuous sleep deprivation (SD). Two, novel, interesting and short (6 min) language tests, known (by brain imaging) to have predominantly a PFC focus, were given, once, towards the end of SD: (i) the Haylings test – which measures the capacity to inhibit strong associations in favour of novel responses, and (ii) a variant of the word fluency test – innovation in a verb-to-noun association. Subjects were exhorted to do their best. Compared with control subjects both tasks were significantly impaired by SD. As a check on the effects on the Haylings test, a repeat study was undertaken with 30 more subjects randomly divided as before. The outcome was similar. Linguistically, sleep loss appears to interfere with novel responses and the ability to suppress routine answers.

Delayed sleep phase syndrome: A placebo‐controlled cross‐over study on the effects of melatonin administered five hours before the individual dim light melatonin onset

Abstract: In a double-blind placebo-controlled cross-over study, 30 patients with Delayed Sleep Phase Syndrome (DSPS) were included, of whom 25 finished the study. Melatonin 5 mg was administered during two weeks in a double-blind setting and two weeks in an open setting successively or interrupted by two weeks of placebo. The study's impact was assessed by measurements of the 24-h curves of endogenous melatonin production and rectal temperature (n=14), polysomnography (n=22), actigraphy (n=13), sleep log (n=22), and subjective sleep quality (n=25). Mean dim light melatonin onset (DLMO) (±SD), before treatment, occurred at 23.17 hours (±138 min). Melatonin was administered five hours before the individual DLMO. After treatment, the onset of the nocturnal melatonin profile was significantly advanced by approximately 1.5 hour. Body temperature trough did not advance significantly. During melatonin use, actigraphy showed a significant advance of sleep onset and polysomnography, a significant decreased sleep latency. Sleep architecture was not influenced. During melatonin treatment patients felt significantly more refreshed in the morning. These results show that analysis of DLMO of patients suffering from DSPS is important both for diagnosis and therapy. These results are discussed in terms of the biochemistry of the pineal.

Autonomic markers of arousal during sleep in patients undergoing investigation for obstructive sleep apnoea, their relationship to EEG arousals, respiratory events and subjective sleepiness

Abstract: Estimating the degree of sleep fragmentation is an important part of a respiratory sleep study and is conventionally measured using EEG micro arousals or is inferred indirectly from respiratory abnormalities such as apnoeas and desaturations. There is a need for less labour-intensive measures of sleep fragmentation, and transient rises in blood pressure and heart rate may fulfil this role. Forty unselected sleep clinic referrals undergoing investigation for possible obstructive sleep apnoea (OSA) were studied with one night of polysomnography. Three conventional indices of sleep fragmentation (EEG micro arousals, apnoea/hypopnoea index (AHI) and oxygen saturation dip rate (SaO2 dips)) and two autonomic indices (heart rate and blood pressure rises) have been compared. Correlations between these five indices ranged from r=0.38 to r=0.73. Of the two autonomic indices, the correlations for blood pressure rises with SaO2 dips and EEG micro arousals were stronger (r=0.71 and r=0.65, respectively) than those for heart rate rises (0.55 and 0.51). All indices of sleep fragmentation, apart from heart rate rises, were similar in their correlation with subjective sleepiness (r-values 0.21-0.36). Arousals implied from blood pressure rises (using pulse transit time) can be measured easily, are objective, and appear no worse at predicting subjective sleepiness than either EEG micro arousals or AHI. They may therefore provide a useful alternative to manual scoring of micro arousals from the EEG as an index of sleep fragmentation in sleep clinic patients undergoing investigation for possible OSA.

Promoting alertness with a short nap during a night shift

Abstract: The use of a short (< 1 h) nap in improving alertness during the early morning hours in the first night shift was examined under laboratory conditions. The study contained four experimental, non-consecutive night shifts with a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night shift without a nap served as a control condition. Each experimental shift was followed by daytime sleep. Fourteen experienced male shift workers went through all of the experimental conditions. The results showed that the naps improved the ability to respond to visual signals during the second half of the night shift. Physiological sleepiness was alleviated by the early naps, as measured 50 min after awakening, but not at the end of the shift. Subjective sleepiness was somewhat decreased by the naps. The naps produced sleep inertia which lasted for about 10-15 min. Daytime sleep was somewhat impaired by the 50 min naps. The study shows that a nap shorter than 1 h is able to improve alertness to a certain extent during the first night shift.

Correlations among Epworth Sleepiness Scale scores, multiple sleep latency tests and psychological symptoms

Abstract: The aim of this study was to identify factors other than objective sleep tendency associated with scores on the Epworth Sleepiness Scale (ESS). There were 225 subjects, of whom 40% had obstructive sleep apnoea (OSA), 16% had simple snoring, and 4.9% had snoring with sleep disruption (upper airway resistance syndrome); 9.3% had narcolepsy and 7.5% had hypersomnolence without REM sleep abnormalities; 12% had chronic fatigue syndrome; 7.5% had periodic limb movement disorder and 3% had diurnal rhythm disorders. ESS, the results of overnight polysomnography and multiple sleep latency test (MSLT) and SCL-90 as a measure of psychological symptoms were recorded. The ESS score and the mean sleep latency (MSL) were correlated (Spearman rho = -0.30, P or = 10 had poor sensitivity and specificity as a predictor of MSL < 10 min or MSL < 5 min. We conclude that the MSLT and the ESS are not interchangeable. The ESS was influenced by psychological factors by which the MSL was not affected. The ESS cannot be used to demonstrate or exclude sleepiness as it is measured by MSLT.

Increased acth and corticosterone secretion induced by different methods of paradoxical sleep deprivation

Abstract: The methods used to induce paradoxical sleep (PS) deprivation are believed to be stressful. In the present study, two methods were compared in regard to their ability to activate the hypothalamic-pituitary-adrenal (HPA) axis. Animals were placed on multiple large (MLP) or small (MSP) platforms or on single large (SLP) or small (SSP) platforms and blood sampled at the end of a 4-day period of PS deprivation (experiment 1) or on Days 1 (short-term) and 4 (long-term) of PS deprivation (experiment 2). ACTH and corticosterone (CORT) levels were determined by RIA. The results of experiment 1 showed that all experimental animals presented increased ACTH response, compared to controls. CORT levels, however, were only elevated in MSP animals, suggesting increased adrenal sensitivity. Experiment 2 showed that ACTH levels of MSP animals were higher than MLP and SSP animals, and that animals placed on the multiple platform tanks showed the highest ACTH levels on Day 4 of manipulation. CORT levels were elevated in the animals kept over small platforms, and these levels where higher on Day 1 than basal and further elevated on Day 4 of PS deprivation. These results indicate that the multiple platform technique induces a distinct activation of the HPA axis, and that PS deprivation may act as an additional stressor.

Sleep bruxism based on self-report in a nationwide twin cohort

Abstract: The relative roles of genetic and environmental factors in bruxism are not known In 1990 a questionnaire sent to the Finnish Twin Cohort yielded responses from 1298 monozygotic and 2419 dizygotic twin pairs aged 33-60 years We used structural equation modelling to estimate genetic and environmental components of variance in the liability to bruxism There was a significant gender difference both in childhood (P = 0001) and adult (P = 0007) bruxism Females compared to males reported childhood bruxism 'often' 52% vs 41% and 'sometimes' 174% vs 173%, and as adults 'weekly' 37% vs 38% and 'monthly' 39% vs 46%, respectively Bruxism in childhood and adulthood is highly correlated (086 in males and 087 in females) The proportion of total phenotypic variance in liability to bruxism attributed to genetic influences in childhood bruxism was 49% (95% CI 37-60%) in males and 64% (55-71%) in females, and for adults 39% (27-50%) among males and 53% (44-62%) among females The correlation between the genetic effects on childhood bruxism and the genetic effects on adult bruxism was estimated in a bivariate model to be 095 (95% CI 094-096) in males and 089 (088-090) in females Bruxism appears to be quite a persistent trait There are substantial genetic effects on bruxism both in childhood and as adults, which appear to be highly correlated

A field study of age and gender differences in habitual adult sleep

Abstract: The sleep of 52 healthy paid subjects (23 male) divided into three age-bands (20–34, 35–49 and 50–70 y) were recorded at night in their homes for a total of 190 subject-nights while following their normal daily activities and habitual sleep-wake schedule. There was a shortening in both nocturnal total sleep period and total sleep time (TST) with age, the oldest group sleeping 46 min less than the youngest. Also, the mid-point of sleep occurred 32 min earlier in the oldest group compared with the youngest group. The reduction in TST with age was due, in part, to increased wake periods within sleep. The youngest subjects showed more Movement Time which progressively decreased with age while the amount of stage 1 increased with age. The amount of slow-wave sleep (SWS, stages 3+4) was reduced, stage 4 was more than halved, while REM was slightly reduced with age. There were far fewer significant gender differences in the sleep variables: males, particularly in the middle and oldest age bands, had more stage 1 than females, while females had more SWS, particularly stage 3, than males. In general, despite relatively limited subject selection criteria, there was good agreement with previous laboratory-based normative sleep values for the effect of age and gender.

Evening administration of melatonin and bright light: interactions on the EEG during sleep and wakefulness.

Abstract: Both the pineal hormone melatonin and light exposure are considered to play a major role in the circadian regulation of sleep. In a placebo- controlled balanced cross-over design, we investigated the acute effects of exogenous melatonin (5 mg p.o. at 20.40 hours) with or without a 3-h bright light exposure (5000 lux from 21.00 hours-24.00 hours) on subjective sleepiness, internal sleep structure and EEG power density during sleep and wakefulness in healthy young men. The acute effects of melatonin, bright light and their interaction were measured on the first day (treatment day), possible circadian phase shifts were assessed on the post-treatment day. On the treatment day, the evening rise in subjective sleepiness was accelerated after melatonin and protracted during bright light exposure. These effects were also reflected in specific changes of EEG power density in the theta/alpha range during wakefulness. Melatonin shortened and bright light increased sleep latency. REMS latency was reduced after melatonin administration but bright light had no effect. Slow-wave sleep and slow-wave activity during the first non-rapid eye movement (NREMS) episode were suppressed after melatonin administration and rebounded in the second NREMS episode, independent of whether light was co-administered or not. Self rated sleep quality was better after melatonin administration whereas the awakening process was rated as more difficult after bright light. On the post-treatment day after evening bright light, the rise in sleepiness and the onset of sleep were delayed, independent of whether melatonin was co-administered or not. Thus, although acute bright light and melatonin administration affected subjective sleepiness, internal sleep structure and EEG power density during sleep and wakefulness in a additive manner, the phase shifting effect of a single evening bright light exposure could not be blocked by exogenous melatonin.

Slow sleep oscillation, rhythmic K‐complexes, and their paroxysmal developments

Abstract: This paper presents the relations between the slow (< 1 Hz) oscillation (characterizing the activity of corticothalamic networks during quiescent sleep in cats and humans), sleep K-complexes, and some paroxysmal developments of sleep patterns. At the cellular level, the slow oscillation is built up by rhythmic membrane depolarizations and hyperpolarizations of cortical neurons. The EEG expression of this activity is marked by periodic K-complexes which reflect neuronal excitation. The slow oscillation triggers, groups and synchronizes other sleep rhythms, such as thalamically generated spindles as well as thalamically and cortically generated delta oscillations. We discuss the distinctness of the slow (< 1 Hz) and delta (1-4 Hz) oscillations. We also show that the slow cortical oscillation underlies the onset of spike-wave seizures during sleep by transforming the periodic K-complexes into recurrent paroxysmal spike-wave complexes.

The nocturnal secretion of cardiac natriuretic peptides during obstructive sleep apnoea and its response to therapy with nasal continuous positive airway pressure

Abstract: The nocturnal secretion profile of the newly identified natriuretic peptide (NP), brain natriuretic peptide (BNP), was studied in 14 patients with obstructive sleep apnoea syndrome (OSAS) (apnoea hypopnoea index: 60.5 +/- 3.4, mean +/- SE) during two separate nights before and during nasal continuous positive airway pressure (NCPAP) therapy. Plasma levels of NPs (atrial natriuretic peptides; ANP and BNP) were measured at 2-h intervals during sleep. Simultaneously, blood pressure was measured by a non-invasive method (Finapres, Ohmeda, Englewood, CO, USA) and urine was collected for determining volume and catecholamine levels. Urinary and serum sodium concentration were determined before and after the study. Eight non-snoring subjects were also studied for the investigation of normal nocturnal profiles of BNP levels. To understand the discrete secretion profiles of the two NPs during sleep, blood was sampled from an additional seven patients every 5 min over a 30-min period around 00.00 and 04.00 hours before NCPAP. In patients with OSAS, plasma BNP levels increased from the beginning of sleep (22:00 h) to the morning (06:00 h) before NCPAP therapy (P < 0.01, ANOVA). Baseline BNP levels were not significantly correlated with patient's clinical and polysomnographic parameters. However, in the latter half of the sleep period (02:00-06:00 h), increases in BNP levels during the night before NCPAP therapy were significantly correlated with blood pressure elevations (systolic: r = 0.784 P < 0.01, diastolic: r = 0.587 P < 0.01) and with apnoea duration (r = 0.582 P < 0.01). In normal subjects BP and BNP levels were not changed significantly during sleep. Plasma BNP levels were well correlated with concomitant ANP levels (P < 0.001). NCPAP therapy reduced ANP and BNP levels during sleep and in the morning (P < 0.01). Plasma levels of BNP at 5 min intervals before NCPAP therapy revealed few variations. On the other hand, ANP levels fluctuated over the 30-min period. Changes in BNP levels during sleep in the patients with OSAS may be related to blood pressure variations, but may be too small to play a significant physiological role in regulating diuresis in OSAS. Further work is required to determine the precise role of dual natriuretic system in cardiovascular load and natriuresis in OSAS.

Impairment of daytime cerebrovascular reactivity in patients with obstructive sleep apnoea syndrome

Abstract: Several studies have demonstrated a clear association between snoring, sleep apnoea and increased risk of stroke. However, the possible role of sleep apnoea in the pathophysiogenetic mechanisms of cerebrovascular disease is still unknown. Our aim in this study was to investigate cerebral haemodynamic changes during the waking state in eight patients with sleep apnoea syndrome (OSAS) by means of transcranial Doppler (TCD). In particular, we studied cerebral vascular reactivity (CVR) to hypercapnia calculated by means of the breath holding index (BHI). The investigation was performed in the early morning, soon after awakening, and in the late afternoon. Data were compared with those of eight healthy subjects matched for age and vascular risk factors. OSAS patients showed significantly lower BHI values with respect to controls both in the morning (0.56 vs. 1.36; P < 0.0001) and in the afternoon (1.12 vs. 1.53; P < 0.0001). In patients, BHI values in the afternoon were significantly higher than in the morning (P < 0.0001). These data demonstrate a diminished vasodilator reserve in OSAS patients, particularly evident in the morning. This reduction of the possibility of cerebral vessels to adapt functionally in response to stimulation could be linked to hyposensitivity of cerebrovascular chemoreceptors after the continuous stress caused by nocturnal hypercapnia.

Dreaming and insomnia: Dream recall and dream content of patients with insomnia

Abstract: The present study investigated dream recall frequency and dream content of patients with insomnia in comparison to healthy controls. Patients’ dream recall frequency was elevated, due mainly to their heightened frequency of nocturnal awakenings. Dream content seems to reflect waking life stressors found in these patients, i.e. dream emotions were more negative and dreams were characterized by themes of depression, ‘negatives’ in self-description and health themes. Patients taking antidepressants showed lower dream recall frequency than patients without any medication; benzodiazepine intake, however, did not affect dream recall frequency. Both drug groups reported more positively toned dreams than drug-free patients. It is suggested that future studies should use more dreams per subject in order to reduce error variance of the dream content measures and more detailed measures of waking life stress.

Behavioural treatment for sleep problems in children with severe learning disabilities and challenging daytime behaviour: Effect on sleep patterns of mother and child

Abstract: Children with sleep problems present serious management problems to their parents. Such children are also more likely to have additional problems, behavioural disturbance being particularly common. This randomized controlled trial of behavioural interventions for the children's sleep problems was conducted to explore the efficacy and mechanisms of treatment in children with the most extreme forms of problems: severe learning disabilities, severe sleep problems and severe daytime challenging behaviour. Fifteen index families received behavioural advice for the child's sleep problem and compared with 15 matched controls who received no such advice. Repeat assessments of the children's and mothers' sleep were made by parental report as well as actometry. Objective changes in the children's sleep quality and quantity were not seen after treatment. However, mothers in the treatment group reported improvements in the children's sleep problems and had an increased sleeping time themselves following treatment. The results indicate that sleep problems can be successfully treated in this group of children, although the mechanisms of treatment may not be as direct as supposed. This has implications for understanding of sleep problems in children with learning disabilities and also for clinical practice, when considering ways of offering help to these highly 'challenged' families.

Paradoxical sleep as a programming system

Abstract: The concept of ‘psychological individuation’ i.e ‘intraspecific variability’ is essential for evolution as stated by Mayr (1958). It has been recently revived by the study of Bouchard (1990) in homozygous twins separated at birth and reared in different environments. These twins still retain identical psychological idiosyncratic reactions. Even if their brains are almost identical at birth, it is most likely that the different epigenetic stimuli from the external world have differently altered many cerebral synaptic circuitry due to the plasticity of the brain. Therefore, in order to maintain an identical psychological profile, there should be a mechanism which would reinforce the genetic programmation of the central nervous system either in reinforcing or erasing special genetic circuitry which would be stimulated during previous and/or subsequent waking periods. In ectothermic vertebrates, in immature mammals or sometimes in mature birds, this programming can be effectuated by neurogenesis. After neurogenesis has stopped in mammals, paradoxical sleep would be well suited for reinforcing the genetic programming during sleep. The patterns of portogeniculo-occipital (PGO) activity (which depend upon genetic factors) would be responsible for this function, together with the theta activity of the hippo-campus (read out of previous waking events) and fast cortical EEG. This programming would activate all the brain including the pyramidal motor system while movements would be suppressed by the system controlling muscle atonia.

Brain temperature dependent changes in the electroencephalogram power spectrum of humans and animals

Abstract: In animals, changes in brain temperature induce a shift in frequencies in the electroencephalogram (EEG). Given the large decreases in body and brain temperature that occur during hibernation, putative functions that were previously ascribed to certain EEG frequencies are no longer valid because of the progressive shift away from the original frequency. In the present review it is proposed that even moderate temperature changes in humans and animals, such as those across the circadian or menstrual cycle, or induced by drugs, have a significant effect on EEG frequencies and the corresponding power spectrum. Alterations in the relative EEG power spectrum, in studies where body temperature also changes, may not be a direct cause of the treatment under investigation, but a consequence of effects on body or brain temperature. However, these effects on the EEG power spectrum are usually interpreted to result directly from the experimental treatment.

Functional brain imaging of human sleep

Abstract: This paper presents an overview of the contribution of functional brain mapping to the study of human sleep. Early studies were essentially successful in describing the variations of the global level of cerebral metabolism. More recently, regional distribution of cerebral blood flow was reported. The results suggest that the permissive and executive processes of slow wave sleep and REM sleep are similar in humans and in animals. They also show cortical blood flow distributions specific to each sleep stage. The cellular mechanisms underlying the involvement of these cortical areas in sleep are not yet precisely known. They should be looked for by further investigations in animals. Future research in functional neuroimaging will attempt to explore functional and, hopefully, effective connectivity between cerebral areas involved in sleep processes. This final goal will probably require the co-registration of two or more brain imaging techniques to precisely describe the spatio-temporal course of neuronal interactions occurring during sleep.

Sleep apnoea in endocrine diseases

Abstract: The pertinent literature on the prevalence, clinical manifestations and pathogenic mechanisms of sleep apnoea (SA) in endocrine diseases, namely acromegaly, Cushing syndrome, hypothyroidism and diabetes mellitus was reviewed. An increased prevalence is well documented in patients with active and treated acromegaly. While most authors report peripheral obstruction, due to hypertrophy of tongue and pharyngeal tissues, to be the cause of SA in acromegaly, some findings argue for a role of hormone-induced changes of central respiratory control. SA is also more common in hypothyroidism, especially when myxedema is present. The associated edema and myopathy appear to be of pathogenic importance. Thyroxin substitution is frequently effective for the treatment of SA but nCPAP can be necessary initially and in some patients even after remission of clinical signs of hypothyroidism. In Cushing disease and syndrome, parapharyngeal fat accumulation can cause SA, but no epidemiological information is available. In non insulin dependent diabetes (NIDDM), obesity is the common risk factor for both, nocturnal hypoxia and insulin resistance. In IDDM, the development of autonomic neuropathy may predispose to SA. Where treatment of the underlying endocrine disease is unable cure the associated SA, nCPAP is usually the treatment of first choice. More prospective studies are clearly needed to establish prevalences and resolve the controversies regarding pathogenesis.

The clinical diagnosis of the narcoleptic syndrome

Abstract: Sleep-wake habits and control of postural muscle tone were investigated by self-report questionnaire in 183 subjects considered to have the narcoleptic syndrome, 62 subjects with hypersomnia and 10 with obstructive sleep apnoea. Results were compared with those in a group of 188 control subjects with normal sleep wake habits. Excessive daytime sleepiness, determined by the Epworth Sleepiness Scale (ESS), was five times greater in the narcoleptic syndrome than in control subjects (score range 0-24, mean scores +/-SD 19.6+/-3.0; and 4.5+/-3.3 respectively; P<0.001). The propensity to cataplexy, as determined by a rating scale developed to estimate the likelihood of loss of postural tone in response to sudden emotional stimuli, including laughter, was 10 times greater in narcoleptic syndrome than in control subjects (postural atonia total score range 0-600; mean + SD 334+/-122 and 28+/-45, respectively; P<0.001). Narcoleptics had more disturbances of night sleep than controls with episodes of muscle jerking, sleep walking, sleep talking and sleep terrors, as well as sleep paralysis, and higher insomnia self-rating scores. Sleep latency from bedtime to sleep-onset time was shorter in narcoleptics than controls. The hypersomniac group of 62 subjects was heterogeneous. Subsequent investigation showed that 18 subjects (29%) had idiopathic hypersomnia, four (6%) 'incomplete' narcolepsy without cataplexy and 10 (16%) hypersomnia accompanying a mood disorder. The mean ESS scores in this group and in subjects with obstructive sleep apnoea were comparable to those of the narcoleptic syndrome subject group. Mean postural atonia scores were similar to those of control subjects.

Temporal evolution of coherence and power in the human sleep electroencephalogram

Abstract: Coherence analysis of the human sleep electroencephalogram (EEG) was used to investigate relations between brain regions. In all-night EEG recordings from eight young subjects, the temporal evolution of power and coherence spectra within and between cerebral hemispheres was investigated from bipolar derivations along the antero-posterior axis. Distinct peaks in the power and coherence spectra were present in NREM sleep but not in REM sleep. They were situated in the frequency range of sleep spindles (13-14 Hz), alpha band (9-10 Hz) and low delta band (1-2 Hz). Whereas the peaks coincided in the power and coherence spectra, a dissociation of their temporal evolution was observed. In the low delta band, only power but not coherence showed a decline across successive NREM sleep episodes. Moreover, power increased gradually in the first part of a NREM sleep episode, whereas coherence showed a rapid rise. The results indicate that the intrahemispheric and interhemispheric coherence of EEG activity attains readily a high level in NREM sleep and is largely independent of the signal amplitude.

Effect of modafinil on plasma melatonin, cortisol and growth hormone rhythms, rectal temperature and performance in healthy subjects during a 36 h sleep deprivation.

Abstract: Modafinil is an alerting substance which has been used successfully to treat narcolepsy. Nothing is known about its effect on hormone secretions. For this purpose, eight healthy young men were enrolled in a double blind trial to test the effects of modafinil on daily plasma melatonin, cortisol and growth hormone (GH) rhythms. Blood was sampled for hormone assays, every hour during the daytime and every 30 min during the nighttime. In addition, rectal temperature and mental performances were determined during the study which comprised 3 sessions, two weeks apart: a 24 h control session including a night with sleep (S1) and two 48 h sessions S2 and S3 with a sleep-deprived night (N1) followed by a recovery night (N2). Modafinil (300 mg x 2) or placebo were randomly attributed during N1 at 22 h and 8 h. As expected, performance was improved after modafinil administration and body temperature was maintained or increased. Plasma melatonin and cortisol profiles were similar after modafinil and placebo administration. The levels observed during the recovery and the control nights (N2) displayed no difference. For GH, during both sleep deprived nights, secretion was dramatically reduced compared with the control one, although the number of secretory episodes was unchanged. These data show that the alerting property of modafinil is not related to an alteration of hormone profiles and suggest that the acute modafinil administration is devoid of short-term side-effects.

Insomnia in an 80-year-old population: Relationship to medical, psychological and social factors

Abstract: In this study, insomnia in 80-year-olds was related to medical, psychological and social factors. The data were based on examinations every year in people aged between 80 and 89 years. Of 333 people living in the city of Lund and born in 1908, 67% participated. Increased severity of insomnia was significantly associated with use of diuretics, other cardiovascular drugs, hypnotics and laxatives, and with nervousness, difficulty relaxing, anorexia, nausea, constipation, backache, feeling cold, sweating, loss of weight, dizziness, depression, general fatigue, exhaustion, angina pectoris, cardiac insufficiency, worsened objective and subjective health, presence of negative T-waves on ECG, anxiety, total life satisfaction, neuroticism, disbelief in a just world, feeling lonely and lower survival rates. Thus insomnia has widespread associations with different aspects of life in 80-year-olds.

A dose-response study of total sleep time and the ability to maintain wakefulness.

Abstract: The apparent connection between sleep debt, performance decrements and workplace accidents has generated a need for feasible vigilance tests that focus on the quantification of daytime sleepiness in occupational settings. The objective of this study was to evaluate the sensitivity of the Maintenance of Wakefulness Test (MWT) to acute sleep deprivation of various doses. Eight healthy female volunteers, mean age 28.9 years (range 23-36), participated in this laboratory study. After an adaptation night, the subjects were assigned to four counterbalanced, randomly ordered night sleep conditions. These four conditions allowed for a time in bed (TIB) of 0, 2, 4 or 8 h, producing a total sleep time of 0, 113, 218 and 427 min, respectively. The ability to sustain wakefulness was measured after the TIB period at 11.00 and 17.00 hours by the MWT. Analysis of variance with repeated measures was used to study the dependence of MWT sleep latencies on the immediately prior TIB period. Both the latency of stage 1 sleep onset and the appearance of slow eye movements reduced significantly with increased sleep loss. The quantitative relationship between the previous total sleep time and the subsequent MWT sleep latencies followed an exponentially decaying function showing a high sensitivity to acute, severe night sleep loss but low sensitivity to less severe sleep restrictions. It is concluded that the MWT seems to be a sensitive method for the estimation of acute sleep deprivation. The test results appear, however, non-linearly related to the earlier sleep debt.

Changes in sleepiness and body temperature precede nocturnal sleep onset :evidence from a polysomnographic study in young men

Abstract: Recent research has shown a close temporal relationship between the nocturnal decrease in rectal core temperature and the initiation of sleep. However, there is not yet a clear temporal relationship between changes in peripheral and core temperatures and nocturnal sleep onset. We recorded body temperatures in 14 adult males (age +/- SEM = 22.1 +/- 0.6 y), who attended the sleep laboratory for an adaptation night and two counterbalanced experimental sessions. Subjects self-selected lights-out on one experimental night (the Habitual Sleep condition). To determine the relationship between body temperature changes and sleep onset, lights out was delayed until after 01.00 hours on the other experimental night (Delayed Sleep condition). Individual datasets in both conditions were expressed relative to the time of sleep onset in the Habitual Sleep condition only, so that they were aligned at identical clock times. Saliva samples confirmed that mean dim light melatonin onset (DLMO) occurred at 00.10 +/- 00.16 hours in the Delayed Sleep condition, which was after habitual sleep onset at 23.44 +/- 00.08 hours. Rectal core temperature (Tc) decreased significantly over time only in the Habitual Sleep condition (P < 0.01). For the 20 min before habitual sleep onset, Delayed Sleep Tc was on average 0.1 degree C higher than Tc in the Habitual Sleep condition (P < 0.01). The greater decline in Habitual Sleep Tc was associated with significantly increased peripheral hand and foot skin temperatures before sleep (both P < 0.05). Subjective sleepiness measures were higher in the Habitual Sleep onset condition from 150 min prior until sleep onset (P < 0.01). From these results it is reasonable to infer that a sequence of thermoregulatory and sleep propensity changes occur before, but are associated with habitual sleep onset, as the changes are significantly attenuated if sleep is delayed.

Sleep fragmentation and daytime vigilance in patients with OSA treated by surgical maxillomandibular advancement compared to CPAP therapy.

Abstract: Impaired vigilance is a frequent daytime complaint of patients with obstructive sleep apnoea (OSA). To date, continuous positive airway pressure (CPAP) is a well established therapy for OSA. Nevertheless, in patients with certain craniofacial characteristics, maxillomandibular advancement osteotomy (MMO) is a promising surgical treatment. Twenty-four male patients with OSA (pretreatment respiratory disturbance index (RDI) 59.3 SD +/- 24.1 events/h) participated in this investigation. The mean age was 42.7 +/- 10.7 years and the mean body mass index was 26.7 +/- 2.9 kg/m2. According to cephalometric evaluation, all patients had a narrow posterior airway space, more or less due to severe maxillary and mandibular retrognathia. All patients except two were treated first with CPAP for at least 3 months and afterwards by MMO. Two patients only tolerated a CPAP trial for 2 nights. Polysomnographic investigation and daytime vigilance were assessed before therapy, with CPAP therapy and 3 months after surgical treatment. Patients' reports of impaired daytime performance were confirmed by a pretreatment vigilance test using a 90-min, four-choice reaction-time test. The test was repeated with effective CPAP therapy and postoperatively. Daytime vigilance was increased with CPAP and after surgical treatment in a similar manner. Respiratory and polysomnographic patterns clearly improved, both with CPAP and after surgery, and showed significant changes compared to the pretreatment investigation. The RDI decreased significantly, both with CPAP (5.3 +/- 6.0) and postoperatively (5.6 +/- 9.6 events/h). The percentages of non-rapid eye movement Stage 1 (NREM 1) sleep showed a marked decrease (with CPAP 8.2 +/- 3.6% and after MMO 8.2 +/- 4.4% vs. 13.3 +/- 7.4% before treatment), whereas percentages of slow wave sleep increased significantly from 8.0 +/- 6.1% before therapy to 18.2 +/- 12.8 with CPAP and 14.4 +/- 7.3% after MMO. The number of awakenings per hour time in bed (TIB) was significantly reduced after surgery (2.8 +/- 1.3), compared to both preoperative investigation (baseline 4.2 +/- 2.0 and CPAP 3.4 +/- 1.5). Brief arousals per hour TIB were reduced to half with CPAP (19.3 +/- 20.0) and after MMO (19.7 +/- 13.6), compared to baseline (54.3 +/- 20.0). We conclude that the treatment of OSA by MMO in carefully selected cases has positive effects on sleep, respiration and daytime vigilance, which are comparable to CPAP therapy.

Reactivation of neuronal ensembles in hippocampal dentate gyrus during sleep after spatial experience

Abstract: Patterns of neuronal activity recorded in CA1 of the hippocampus and in neocortex during waking-behavior, are reactivated during subsequent slow-wave sleep (SWS). It has been suggested that this reactivation may originate in the hippocampal CA3 region, where modifiable excitatory recurrent connections are abundant and where sharp-waves, in which the reactivation is most robust, appear to arise. The present experiment investigated whether ensemble firing patterns of granule cells in the fascia dentata (FD), an area ‘upstream’ from CA3, are also reactivated during sleep. Populations of FD granule cells were recorded from during spatial behavior and during prior and subsequent SWS. Firing rate correlations between cell-pairs with overlapping place fields were significantly enhanced during post behavioral sleep compared to pre behavioral sleep. Correlations between cells with non-overlapping place fields or which were silent during maze behavior, were not changed. Thus, reactivation of experience-specific correlation states also occurs in granule cells during sleep. Because these cells do not have excitatory interconnections, but form a major input to CA3 pyramidal cells, current models predicted that sleep reactivation would appear first in CA3. There are, however, both extensive polysynaptic excitatory interactions among granule cells and feedback from CA3 pyramidal cells. Granule cells also receive indirect input from neocortical regions known to undergo trace reactivation. Although a simple model for a CA3 origin of the reactivation phenomenon cannot be confirmed, the present results extend our understanding of the generality of this phenomenon.

The siesta culture concept is not supported by the sleep habits of urban mexican students

Abstract: Evidence in support for the concept of the so-called 'siesta culture' is not well developed and has, to date, relied largely on qualitative anthropological data. Presumably such cultures are characterized by a strong tendency for daytime naps and daytime sleepiness, phenomena which may partially represent the effects of geographic, climatic or light conditions and/or cultural influences. In this study we surveyed the nocturnal sleep habits and daytime sleep tendencies of 577 Mexican college students residing in Mexico City (19 degrees N latitude). Results indicated a number of parallels between the reported sleep habits of these students and those reported from other cultures at latitudes far to the north (North America, Europe), such as longer sleep at the weekends, an association between snoring and daytime sleepiness and a lack of relationship between nocturnal sleep duration and the reported tendency to nap. There was some suggestion that these Mexican students may actually nap less when compared to other college student populations. Taken together, these results call into question what is meant by the concept of a 'siesta culture', at least in this urban, educated, upper social economic scale (SES) population, and suggest that future studies in equatorial regions be undertaken to further appreciate the role of climate, photoperiod and/or culture in the tendency for humans to nap during the day.

A new method for detecting state changes in the EEG: exploratory application to sleep data

Abstract: SUMMARY A new statistical method is described for detecting state changes in the electroencephalogram (EEG), based on the ongoing relationships between electrode voltages at different scalp locations. An EEG sleep recording from one NREM-REM sleep cycle from a healthy subject was used for exploratory analysis. A dimensionless function defined at discrete times ti, u(ti), was calculated by determining the log-likelihood of observing all scalp electrode voltages under the assumption that the data can be modeled by linear combinations of stationary relationships between derivations. The u(ti), calculated by using independent component analysis, provided a sensitive, but non-specific measure of changes in the global pattern of the EEG. In stage 2, abrupt increases in u(ti) corresponded to sleep spindles. In stages 3 and 4, low frequency (& 0.6 Hz) oscillations occurred in u(ti) which may correspond to slow oscillations described in cellular recordings and the EEG of sleeping cats. In stage 4 sleep, additional irregular very low frequency (& 0.05‐0.2 Hz) oscillations were observed in u(ti) consistent with possible cyclic changes in cerebral blood flow or changes of vigilance and muscle tone. These preliminary results suggest that the new method can detect subtle changes in the overall pattern of the EEG without the necessity of making tenuous assumptions about stationarity.

Heart rate variability and apnea during sleep in Down's syndrome

Abstract: Autonomic system dysfunction has been reported to occur frequently in patients with Down's syndrome (DS) and is constituted mainly by an imbalance between the sympathetic and vagal systems. The analysis of heart rate variability (HRV) during sleep is a quantitative reliable method for studying such a mechanism, but it has not yet been extensively and adequately applied in DS. In this study, HRV during sleep was evaluated in seven DS patients and in six normal controls, by also controlling for the presence of sleep apnea or arousal. The main results were an increased sympathetic function (low-frequency component of HRV) and a decreased vagal activity (high-frequency component of HRV) in DS with respect to normal controls, during apnea-free periods. Moreover, the presence of apnea, in DS, induced a further significant increase in low-frequency and very low-frequency components of HRV during sleep Stage 2. This study provides additional evidence of a brainstem dysfunctioning in DS, responsible for the abnormal imbalance between the sympathetic and vagal systems and confirms the brainstem involvement already suggested in the literature in order to explain brainstem-auditory evoked potential abnormalities and central sleep apnea in these patients.