Timing the end of nocturnal sleep

One night of partial sleep deprivation affects habituation of hypothalamus and skin conductance responses

Sleep disturbances are prevalent in clinical anxiety, but it remains unclear whether they are cause and/or consequence of this condition. Fear conditioning constitutes a valid laboratory model for the acquisition of normal and pathological anxiety. To explore the relationship between disturbed sleep and anxiety in more detail, the present study evaluated the effect of partial sleep deprivation (SD) on fear conditioning in healthy individuals. The neural correlates of 1) nonassociative learning and physiological processing and 2) associative learning (differential fear conditioning) were addressed. Measurements entailed simultaneous functional MRI, EEG, skin conductance response (SCR), and pulse recordings. Regarding nonassociative learning, partial SD resulted in a generalized failure to habituate during fear conditioning, as evidenced by reduced habituation of SCR and hypothalamus responses to all stimuli. Furthermore, SCR and hypothalamus activity were correlated, supporting their functional relationship. Regarding associative learning, effects of partial SD on the acquisition of conditioned fear were weaker and did not reach statistical significance. The hypothalamus plays an integral role in the regulation of sleep and autonomic arousal. Thus sleep disturbances may play a causal role in the development of normal and possibly pathological fear by increasing the susceptibility of the sympathetic nervous system to stressful experiences.

Deepening sleep by hypnotic suggestion

STUDY OBJECTIVES

Slow wave sleep (SWS) plays a critical role in body restoration and promotes brain plasticity; however, it markedly declines across the lifespan. Despite its importance, effective tools to increase SWS are rare. Here we tested whether a hypnotic suggestion to "sleep deeper" extends the amount of SWS.

DESIGN

Within-subject, placebo-controlled crossover design.

SETTING

Sleep laboratory at the University of Zurich, Switzerland.

PARTICIPANTS

Seventy healthy females 23.27 ± 3.17 y.

INTERVENTION

Participants listened to an auditory text with hypnotic suggestions or a control tape before napping for 90 min while high-density electroencephalography was recorded.

MEASUREMENTS AND RESULTS

After participants listened to the hypnotic suggestion to "sleep deeper" subsequent SWS was increased by 81% and time spent awake was reduced by 67% (with the amount of SWS or wake in the control condition set to 100%). Other sleep stages remained unaffected. Additionally, slow wave activity was significantly enhanced after hypnotic suggestions. During the hypnotic tape, parietal theta power increases predicted the hypnosis-induced extension of SWS. Additional experiments confirmed that the beneficial effect of hypnotic suggestions on SWS was specific to the hypnotic suggestion and did not occur in low suggestible participants.

CONCLUSIONS

Our results demonstrate the effectiveness of hypnotic suggestions to specifically increase the amount and duration of slow wave sleep (SWS) in a midday nap using objective measures of sleep in young, healthy, suggestible females. Hypnotic suggestions might be a successful tool with a lower risk of adverse side effects than pharmacological treatments to extend SWS also in clinical and elderly populations.

Relationships between housing and food insecurity, frequent mental distress, and insufficient sleep among adults in 12 US States, 2009

INTRODUCTION

Housing insecurity and food insecurity may be psychological stressors associated with insufficient sleep. Frequent mental distress may mediate the relationships between these variables. The objective of this study was to examine the relationships between housing insecurity and food insecurity, frequent mental distress, and insufficient sleep.

METHODS

We analyzed data from the 2009 Behavioral Risk Factor Surveillance System in 12 states. Housing insecurity and food insecurity were defined as being worried or stressed "sometimes," "usually," or "always" during the previous 12 months about having enough money to pay rent or mortgage or to buy nutritious meals.

RESULTS

Of 68,111 respondents, 26.4% reported frequent insufficient sleep, 28.5% reported housing insecurity, 19.3% reported food insecurity, and 10.8% reported frequent mental distress. The prevalence of frequent insufficient sleep was significantly greater among those who reported housing insecurity (37.7% vs 21.6%) or food insecurity (41.1% vs 22.9%) than among those who did not. The prevalence of frequent mental distress was also significantly greater among those reporting housing insecurity (20.1% vs 6.8%) and food insecurity (23.5% vs 7.7%) than those who did not. The association between housing insecurity or food insecurity and frequent insufficient sleep remained significant after adjustment for other sociodemographic variables and frequent mental distress.

CONCLUSION

Sleep health and mental health are embedded in the social context. Research is needed to assess whether interventions that reduce housing insecurity and food insecurity will also improve sleep health and mental health.

Chronic stress exposure decreases the cortisol awakening response in healthy young men

Academic examination is a major stressor for students in China. Investigation of stress-sensitive endocrine responses to major examination stress serves as a good model of naturalistic chronic psychological stress in an otherwise healthy population. The cortisol awakening response (CAR) is an endocrine marker of the hypothalamic-pituitary-adrenocortical (HPA) axis in response to stress. However, it remains unknown how chronic examination stress impacts the CAR in a young healthy population To exclude the influence of sex effects on hormone level, the CAR and psychological stress responses were assessed on two consecutive workdays in 42 male participants during their preparations for the Chinese National Postgraduate Entrance Exam (NPEE) and 21 non-exam, age-matched male comparisons. On each day, four saliva samples were collected immediately after awakening, 15 minutes, 30 minutes and 60 minutes after awakening. The waking level (S1), the increase within 30 minutes after awakening (R30), the area under the curve with respect to ground (AUCg), and the area under the curve with respect to increase (AUCi) were used to quantify the CAR. Psychological stress and anxiety were assessed by the Perceived Stress Scale and the Spielberger State-Trait Anxiety Inventory, respectively. Male participants in the exam group had greater perceived stress and anxiety scores relatibe to the non-exam group. Both R30 and AUCi in the exam group were significantly lower than the comparison group and this effect was most pronounced for participants with high levels of perceived stress in the exam group. Perceived stress and anxiety levels were negatively correlated with both R30 and AUCi. Chronic examination stress can lead to the decrease of CAR in healthy young men, possibly due to reduced HPA axis activity under long-term sustained stress.

In pre-school children, sleep objectively assessed via sleep-EEGs remains stable over 12 months and is related to psychological functioning, but not to cortisol secretion

STUDY OBJECTIVES

Cross-sectional studies provide evidence that in pre-schoolers poor sleep is by this age already associated with both poor psychological functioning and an increased cortisol secretion. However, long-term studies on the stability of sleep in pre-schoolers are scarce. The aim of the present study was therefore to investigate objectively assessed sleep in pre-schoolers longitudinally, and to predict sleep, psychological functioning and cortisol secretion prospectively as a function of sleep 12 months earlier.

METHOD

A total of 58 pre-schoolers (mean age: 5.43 years; 47% females) were re-assessed 12 months later (mean age: 6.4 years). Sleep-EEG recordings were performed, saliva cortisol was analysed, and parents and experts rated children's psychological functioning.

RESULTS

Longitudinally, poor objective sleep at age 5.4 years was associated with poor objective sleep and psychological difficulties but not cortisol secretion 12 months later. At age 6.4 years, poor sleep was concurrently associated with greater psychological difficulties and increased cortisol secretion.

CONCLUSION

In pre-schoolers, poor sleep objectively assessed at the age of 5.4 years was associated with poor sleep and psychological difficulties one year later. Data indicate that in pre-schoolers, sleep remains stable over a 12-months-period. Pre-schoolers with poor sleep appear to be at risk for developing further psychological difficulties.

Influences of early shift work on the diurnal cortisol rhythm, mood and sleep: within-subject variation in male airline pilots

We aimed to investigate how early and late work shifts influenced the diurnal cortisol rhythm using a within-subjects study design. Participants were 30 healthy male non-smoking pilots, mean age 39.4, employed by a short-haul airline. The standard rotating shift pattern consisted of 5 early shifts (starting before 0600 h), followed by 3 rest days, 5 late shifts (starting after 1200 h) and 4 rest days. Pilots sampled saliva and completed subjective mood ratings in a logbook 6 times over the day on two consecutive early shift days, two late days and two rest days. Sampling was scheduled at waking, waking+30 m, waking+2.5 h, waking+8 h, waking+12 h and bedtime. Waking time, sleep duration, sleep quality and working hours were also recorded. Cortisol responses were analysed with repeated measures analysis of variance with shift condition (early, late, rest) and sample time (1-6) as within-subject factors. Early shifts were associated with a higher cortisol increase in response to awakening (CAR(i)), a greater total cortisol output over the day (AUC(G)) and a slower rate of decline over the day than late shifts or rest days. Early shifts were also associated with shorter sleep duration but co-varying for sleep duration did not alter the effects of shift on the cortisol rhythm. Both types of work shift were associated with more stress, tiredness and lower happiness than rest days, but statistical adjustment for mood ratings did not alter the findings. Early shift days were associated with significantly higher levels of circulating cortisol during waking hours than late shifts or rest days.

Psychological and environmental correlates of HPA axis functioning in parentally bereaved children: preliminary findings

This study examined bereaved children's HPA-axis functioning (cortisol awakening response; CAR) in relation to psychological distress, coping, and surviving parents' grief reactions. Participants included 38 children (20 girls) with recent parental loss (previous 6 months) and 28 of their surviving caregivers (23 women) who were assessed using self-report instruments and in-person, semistructured interviews. Interviews involved discussions about the child's thoughts and feelings related to the loss. Participants provided 3 saliva samples at home (awakening, 30 minutes later, and evening) over 3 successive days, beginning on the day following the interview. Results show a significant relation between dampening of the child's Day 1 CAR and more symptoms of anxiety (r = -.45), depression (r = -.40), posttraumatic stress (r = -.45), and maladaptive grief (r = -.43), as well as higher levels of avoidant coping (r = -.53). Higher levels of parental maladaptive grief were also associated (r = -.47) with a dampening of the child's Day 1 CAR. Our results raise the possibility that blunted CAR may be a result of accumulating allostatic load and/or a result of emotionally challenging events (discussions regarding the deceased) and their subsequent processing (or lack thereof) within the family, which may be particularly stressful for those bereaved children experiencing high levels of psychological distress, avoidant coping, and parental maladaptive grief.

Effects of chronic khat use on cardiovascular, adrenocortical, and psychological responses to stress in men and women

BACKGROUND

Khat is a psychostimulant plant widely used in Africa and its use has been growing rapidly in Europe and North America.

OBJECTIVES

We investigated effects of chronic khat (Catha edulis) use on cardiovascular, adrenocortical, and psychological responses to acute stress.

METHODS

Chronic khat users and nonusers were compared on physiological measures and mood reports in a cross-sectional, mixed design. Measurements were conducted during 24-hour ambulatory monitoring and during a laboratory session. A total of 152 participants (58 women) were recruited by flyers posted around Sana'a University campus and the surrounding community in Sana'a, Yemen. Salivary cortisol and self-report measures were collected during a 24-hour ambulatory period prior to a lab testing session. In addition, blood pressures (BP), salivary cortisol, and mood measures were assessed during rest and in response to acute mental stress.

RESULTS

Khat users exhibited enhanced evening and attenuated morning cortisol levels, reflecting a blunted diurnal pattern of adrenocortical activity compared to nonusers. Khat users reported greater negative affect during the ambulatory period and during the laboratory session. In addition, they exhibited attenuated BP responses to stress.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

These novel results demonstrate altered adrenocortical activity and increased dysphoric mood among khat users. The extent to which these associations are due to effects of chronic khat use per se or instead reflect predisposing risk factors for khat use is yet to be determined.

Increased cerebral blood flow in the right frontal lobe area during sleep precedes self-awakening in humans

BACKGROUND

Some people can subconsciously wake up naturally (self-awakening) at a desired/planned time without external time stimuli. However, the underlying mechanism regulating this ability remains to be elucidated. This study sought to examine the relationship between hemodynamic changes in oxyhemoglobin (oxy-Hb) level in the prefrontal cortex and sleep structures during sleep in subjects instructed to self-awaken.

RESULTS

Fifteen healthy right-handed male volunteers with regular sleep habits participated in a consecutive two-night crossover study. The subjects were instructed to wake up at a specified time ("request" condition) or instructed to sleep until the morning but forced to wake up at 03:00 without prior notice ("surprise" condition). Those who awoke within ± 30 min of the planned waking time were defined as those who succeeded in self-awakening ("success" group). Seven subjects succeeded in self-awakening and eight failed.No significant differences were observed in the amounts of sleep in each stage between conditions or between groups. On the "request" night, an increase in oxy-Hb level in the right prefrontal cortex and a decrease in δ power were observed in the "success" group around 30 min before self-awakening, whereas no such changes were observed in the "failure" group. On the "surprise" night, no significant changes were observed in oxy-Hb level or δ power in either group.

CONCLUSIONS

These findings demonstrate a correlation between self-awakening and a pre-awakening increase in hemodynamic activation in the right prefrontal cortex, suggesting the structure's contribution to time estimation ability.

Sleep timing may modulate the effect of sleep loss on testosterone

BACKGROUND

Sleep loss has been shown to reduce secretory activity of the pituitary-gonadal axis in men, but the determinants of this effect are unknown.

OBJECTIVE

To discriminate the effects of sleep duration and sleep timing on serum concentrations of luteinizing hormone (LH), testosterone (T) and prolactin (PRL).

METHODS

Fifteen young, healthy men (27·1 ± 1·3 years; BMI, 22·9 ± 0·3 kg/m(2) ) were examined in a condition of sleep time restriction to 4 h (bedtime, 02:45 -07:00 h) for two consecutive nights and in a control condition of 8 h regular sleep (bedtime, 22:45-07:00 h). After the second night, serum concentrations of LH, T and PRL were monitored over a 15-h period. In addition, these hormones were measured in serum samples obtained in a further experiment in eight healthy men (24·5 ± 1·1 years; BMI, 23·7 ± 0·6 kg/m(2) ) in the morning after one night of total sleep deprivation, of 4·5 h sleep (bedtime, 22:30-03:30 h), and of regular 7 h sleep (bedtime, 22:30-06:00 h).

RESULTS

Serum LH, T and PRL concentrations showed characteristic diurnal variations across the 15-h period without any differences between the 4- and 8-h sleep conditions. However, total sleep deprivation and 4·5 h of sleep restricted to the first night-half markedly decreased morning T and PRL concentrations (both P ≤ 0·05).

CONCLUSION

Collectively, our data suggest that the effect of sleep restriction on pituitary-gonadal secretory activity may be modulated by sleep timing. While sleep loss in the early part of the night does not affect T and PRL, early awakening and wakefulness during the second part of the night reduces morning circulating T and PRL concentrations.

[The effects of self-awakening on daytime sleepiness]

This study investigated the effects of self-awakening on daytime sleepiness. Eleven undergraduate and graduate students without the habit of self-awakening participated. They were instructed to follow their usual sleep-wake schedule at home during the experimental weeks and were required to awaken at their usual time by themselves every morning for one week without the aid of an alarm (self-awakening condition) or in response to a telephone call from the experimenter every morning for another one week (forced-awakening condition). On the last day of each week, daytime tests were conducted in the laboratory. The participants would arrive at the laboratory 2 h after awakening, and 1 h later, they performed the auditory simple reaction time task, the digit-symbol substitution task, the letter cancellation test, and the multiple sleep latency test, and assessment of sleepiness, fatigue, comfort, and work motivation every 2 h. In the week when the participants underwent the self-awakening condition, self-awakening had a higher success rate (82%) than failure rate (18%) on the seventh day. In comparison with forced-awakening, self-awakening resulted in an improvement in subjective fatigue; however, sleepiness did not deteriorate.

Pre-schoolers suffering from psychiatric disorders show increased cortisol secretion and poor sleep compared to healthy controls

BACKGROUND

Various studies of child cortisol secretion and sleep show a close association between poor sleep, deterioration of the HPA axis and unfavorable psychological functioning. However, there is little evidence as to whether these associations are clearly present in pre-school children suffering from psychiatric disorders.

METHOD

A total of 30 pre-schoolers suffering from psychiatric disorders (anxiety, adjustment disorders, emotional and attachment disorder; hyperactivity or oppositional disorder) and 35 healthy controls took part in the study. Saliva cortisol secretion was assessed both at baseline and under challenge conditions. Sleep was assessed via activity monitoring for seven consecutive days and nights, using a digital movement-measuring instrument. Parents and teachers completed questionnaires assessing children's cognitive, emotional and social functioning. The Berkeley Puppet Interview provided child-based reports of cognitive-emotional processes.

RESULTS

Compared to healthy controls, children suffering from psychiatric disorders had much higher cortisol secretion both at baseline and under challenge conditions. Sleep was also more disturbed, and parents and teachers rated children suffering from psychiatric disorders as cognitively, emotionally and behaviorally more impaired, relative to healthy controls. Children with psychiatric disorders reported being more bullied and victimized.

CONCLUSIONS

In five-year old children the presence of psychiatric disorders is reflected not only at psychological, social and behavioral, but also at neuroendocrine and sleep-related levels. It is likely that these children remain at increased risk for suffering from psychiatric difficulties later in life.

Contribution of norepinephrine to emotional memory consolidation during sleep

BACKGROUND

There is increasing evidence indicating that slow wave sleep (SWS) supports memory consolidation. This effect may in part originate from phasic noradrinergic (NE) activity occurring during SWS in the presence of tonically lowered NE levels. Here, we examined whether NE supports the consolidation of amygdala-dependent emotional memory during SWS.

METHODS

In a double-blind cross-over study, 15 men learned emotional and neutral materials (stories, pictures) in the evening before a 3-h period of early SWS-rich retention sleep, during which either placebo or clonidine, an α2-adrenoceptor agonist which blocks locus coeruleus NE release, was intravenously infused. Memory retrieval as well as affective ratings and heart rate responses to the pictures were assessed 23 h after learning.

RESULTS

Clonidine reduced plasma NE levels but had no effect on SWS. While retention of story content words and pictures per se remained unaffected, clonidine distinctly blocked the superiority of emotional compared to neutral memory for temporal order, with this superiority of emotional over neutral memories observed only in the placebo condition. Heart rate responses to pictures were not affected, but whereas under placebo conditions familiar negative pictures were rated less arousing and with a more negative valence compared to pictures not seen before; these differences were abolished after clonidine.

CONCLUSION

Given that memory for the temporal order of events depends on the hippocampus to a greater extent than item memory, our findings suggest that NE activity during early SWS-rich sleep facilitates consolidation of memories that involve both, a strong amygdalar and hippocampal component.

Suprachiasmatic nucleus and autonomic nervous system influences on awakening from sleep

Awakening from sleep is a clear example of an event for which (biological) clocks are of great importance. We will review some major pathways the mammalian biological clock uses to ensure an efficient and coordinated wake-up process. First we show how this clock enforces daily rhythmicity onto the hypothalamo-pituitary-adrenal (HPA) axis, via projections to neuroendocrine neurons within the hypothalamus. Next we demonstrate how this brain clock controls plasma glucose concentrations, via projections to sympathetic and parasympathetic pre-autonomic neurons within the hypothalamus. Orexin neurons in the lateral hypothalamus appear to be an important hub in this awakening control network.

Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepiness

Patients with idiopathic hypersomnia never feel fully alert despite a normal or long sleep night. The spectrum of the symptoms is insufficiently studied. We interviewed 62 consecutive patients with idiopathic hypersomnia (with a mean sleep latency lower than 8 min or a sleep time longer than 11 h) and 50 healthy controls using a questionnaire on sleep, awakening, sleepiness, alertness and cognitive, psychological and functional problems during daily life conditions. Patients slept 3 h more on weekends, holidays and in the sleep unit than on working days. In the morning, the patients needed somebody to wake them, or to be stressed, while routine, light, alarm clocks and motivation were inefficient. Three-quarters of the patients did not feel refreshed after short naps. During the daytime, their alertness was modulated by the same external conditions as controls, but they felt more sedated in darkness, in a quiet environment, when listening to music or conversation. Being hyperactive helped them more than controls to resist sleepiness. They were more frequently evening-type and more alert in the evening than in the morning. The patients were able to focus only for 1 h (versus 4 h in the controls). They complained of attention and memory deficit. Half of them had problems regulating their body temperature and were near-sighted. Mental fatigability, dependence on other people for awakening them, and a reduced benefit from usually alerting conditions (except being hyperactive or stressed) seem to be more specific of the daily problems of patients with idiopathic hypersomnia than daytime sleepiness.

The cortisol awakening response in patients remitted from depression

An impressive number of data has been accumulated on dysfunctions of the hypothalamo-pituitary-adrenal (HPA) axis and cortisol hypersecretion in depression. To assess the dynamic HPA functioning, the cortisol awakening response (CAR) is an easily accessible and reliable approach. Some data suggest that elevated CAR in depressed patients has trait-like characteristics. Therefore we investigated whether patients in remission from a depressive episode have elevated CAR compared to control subjects. CAR of thirty-eight patients in remission from depression (11 men, 27 women, age range 24-66) and 52 control participants were analyzed (18 men, 34 women, age range 24-63). All patients had experienced ≥3 previous depressive episodes and were off psychotropic medication since at least 3 months. Saliva samples were collected only once, at home, either on weekend or weekday at 0, 15, 30, 45 and 60 min post-awakening. The area under the curve (AUC) above minimum cortisol concentration displayed large interindividual variability (6.4-fold in remitted patients and 8.1-fold in controls, based on 80% range). Investigation of possible variability factors showed that percent explained variance increased from 3.9% when group was considered alone to 8.8%, 12.3% and 19.2% after adjusting for significant effects of weekday vs. weekend, wake-up time and sleep duration, respectively. According to the latter model, AUC was estimated to be 51% higher in remitted patients than in controls (p = 0.007), while a 21% AUC decrease was associated with a 1-h longer sleep duration (p<0.001). In future studies, detection of between-group differences might benefit from adjusting for sleep duration and other possible confounders.

Diurnal fluctuations in subjective sleep time in humans

Humans have the ability to estimate the passage of time in the absence of external time cues. In this study, we subjected 22 healthy males (aged 21.8±1.9 years) to a 40-min nap trial followed by 80min of wakefulness repeated over 28h, and investigated the relationship between various sleep parameters and the discrepancy (ΔST) of time estimation ability (TEA) during sleep, defined by the difference between actual sleep time (ST) and subjective sleep time (sub-ST) in each nap interval. Both ST and sub-ST were significant diurnal fluctuations with the peak in the early morning (9h after dim-light melatonin onset time, 2h after nadir time of core body temperature rhythm), and subjective sleep duration was estimated to be longer than actual times in all nap intervals (sub-ST>ST). There were significant diurnal fluctuations in discrepancy (sub-ST-ST) of TEA during sleep, and the degree of discrepancy correlated positively with increase in the amount of REM sleep and decrease in the amount of slow-wave sleep. These findings suggest that human TEA operates at a certain level of discrepancy during sleep, and that this discrepancy might be related to the biological clock and its associated sleep architecture.

What constitutes too long of a delay? Determining the cortisol awakening response (CAR) using self-report and PSG-assessed wake time

The cortisol awakening response (CAR) is a burst of cortisol in response to awakening from sleep that is superimposed on the circadian rhythm of cortisol. Determination of the CAR is contingent on the timing of sample collection: a delay between waking and collection of the first sample may affect the rise of the CAR, and could explain equivocal findings reported in the literature. We evaluated the impact of a delay between wake time and collection of waking cortisol samples on the CAR. Two methods were used to identify wake time: polysomnography (PSG) and self-report (S-R). Participants (total n=207, mean age 74.0+/-7.2 years) included bereaved older adults (n=35), caregivers (n=50), patients with insomnia and co-morbid medical disorders (n=68), and the healthy older adults (n=54). We used ANOVA to test if a delay >15 min affected the CAR. We also fitted cubic spline models to assess expected cortisol levels, the expected CAR, and the expected decrease in CAR. Wake times measured by PSG and S-R did not differ significantly. Large delays were observed (for both PSG and S-R) between wake time and collection of the waking cortisol sample (24.8+/-32.2 min for PSG and 28.3+/-49.2 min for S-R). Both statistical methods indicated that a delay >15 min between wake time and first cortisol sample collection significantly affected the CAR (p's<.005); later collection times were associated with smaller CAR values. Later collection times and reduced CAR values may affect the interpretation of clinical associations. Our data also show that S-R assessments of wake time perform equally well to PSG for evaluating adherence with CAR sampling procedures.

Sleep, hormones, and memory

Nocturnal sleep is characterized by a unique pattern of endocrine activity, which comprises reciprocal influences on the hypothalamo-pituitary-adrenal (HPA) and the somatotropic system. During early sleep, when slow wave sleep (SWS) prevails, HPA secretory activity is suppressed whereas growth hormone (GH) release reaches a maximum; this pattern is reversed during late sleep when rapid eye movement (REM) sleep predominates. SWS benefits the consolidation of hippocampus-dependent declarative memories, whereas REM sleep improves amygdala-dependent emotional memories and procedural skill memories involving striato-cortical circuitry. Manipulation of plasma cortisol and GH concentration during sleep revealed a primary role of HPA activity for memory consolidation. Pituitary-adrenal inhibition during SWS sleep represents a prerequisite for efficient consolidation of declarative memory; increased cortisol during late REM sleep seems to protect from an overshooting consolidation of emotional memories.

Human models in acute and chronic stress: assessing determinants of individual hypothalamus-pituitary-adrenal axis activity and reactivity

Stress is one of the most significant health problems in modern societies and the 21st century. This explains a pressing need for investigations into the biological pathways linking stress and health. Besides the locus coeruleus-noradrenaline/autonomic (sympathetic) nervous system ( Chrousos and Gold 1992 ), the hypothalamus-pituitary-adrenal (HPA) axis is the major physiological stress response system in the body. Since alterations in HPA axis regulation under basal conditions and in response to acute stress appear to be a close correlate or even a determining factor of the onset of different diseases or disease progression ( Holsboer 1989 ; Chrousos and Gold 1992 ; Tsigos and Chrousos 1994, 2002 ; Stratakis and Chrousos 1995 ; McEwen 1998 ; Heim et al. 2000a ; Raison and Miller 2003 ), the characterization of an individual's HPA axis activity as well as reactivity pattern to psychosocial stress appears to be of major interest. It is obvious that such a research agenda substantially depends on the availability of appropriate measures. However, since the HPA axis is a highly adaptive system which is characterized by marked inter- and intraindividual variability ( Mason 1968 ; Hellhammer et al. 2009 ), the development of such markers of HPA axis regulation in humans was-and still is-a rather challenging task. In this brief review, we focus on findings on two HPA axis measures, namely the cortisol-awakening response (CAR) to assess HPA axis basal activity and the Trier social stress test (TSST) to investigate HPA axis stress reactivity.

The cortisol awakening response: more than a measure of HPA axis function

In most healthy people morning awakening is associated with a burst of cortisol secretion: the cortisol awakening response (CAR). It is argued that the CAR is subject to a range physiological regulatory influences that facilitate this rapid increase in cortisol secretion. Evidence is presented for reduced adrenal sensitivity to rising levels of ACTH in the pre-awakening period, mediated by an extra-pituitary pathway to the adrenal from the suprachiasmatic nucleus (SCN). A role for the hippocampus in this pre-awakening regulation of cortisol secretion is considered. Attainment of consciousness is associated with 'flip-flop' switching of regional brain activation, which, it is argued, initiates a combination of processes: (1) activation of the hypothalamic pituitary adrenal (HPA) axis; (2) release of pre-awakening reduced adrenal sensitivity to ACTH; (3) increased post-awakening adrenal sensitivity to ACTH in response to light, mediated by a SCN extra-pituitary pathway. An association between the CAR and the ending of sleep inertia is discussed.

The effect of self-awakening from nocturnal sleep on sleep inertia

The present study examined the effects of self-awakening on sleep inertia after nocturnal sleep. Ten undergraduate and graduate students participated in the study. Their polysomnograms were recorded for five consecutive nights; the first, second, and third to fifth nights were adaptation, forced-awakening, and self-awakening nights, respectively. Participants rated sleepiness, fatigue, comfort, and work motivation, and these ratings were followed by switching (7 min) and auditory reaction time tasks (6 min), both before bedtime (15 min) and immediately after awakening (4 min x 15 min). Although reaction times on the auditory were task prolonged, and participants complained of feeling uncomfortable immediately after forced-awakening, reaction times were shortened after self-awakening, and the participants did not complain of feeling uncomfortable on these nights. The results of this study suggest that sleep inertia occurs after forced-awakening and that it can be prevented by self-awakening.

Serotonin transporter polymorphism predicts waking cortisol in young girls

Major Depressive Disorder (MDD) is one of the most prevalent and costly of all psychiatric disorders. The hypothalamic pituitary adrenal (HPA)-axis, which regulates the hormonal response to stress, has been found to be disrupted in depression. HPA dysregulation may represent an important risk factor for depression. To examine a possible genetic underpinning of this risk factor without the confound of current or lifetime depression, we genotyped 84 never-disordered young girls, over a third of whom were at elevated risk for depression, to assess the association between a polymorphism in the promoter region of the serotonin transporter (5-HTT) gene and diurnal variation in HPA-axis activity. This 5-HTT-linked polymorphic region (5-HTTLPR) has been previously found to interact with stress to increase risk for depression. We found 5-HTTLPR to be significantly associated with diurnal cortisol levels: girls who were homozygous for the short-allele had higher levels of waking (but not afternoon or evening) cortisol than did their long-allele counterparts. This finding suggests that genetic susceptibility to HPA-axis dysregulation, especially apparent in levels of waking cortisol, is detectable in individuals as young as 9 years of age.

Early morning rise in hypothalamic-pituitary-adrenal activity: a role for maintaining the brain's energy balance

A profound rise in secretory activity in the early morning hours hallmarks the circadian regulation of the hypothalamic-pituitary-adrenal (HPA) stress axis. Functions and mechanisms underlying this regulation are barely understood. We tested the hypothesis that the early morning rise in HPA axis activity originates in part from a negative energy balance due to nocturnal fasting and concomitant increases in cerebral glucose demands. According to a 2x2 design, healthy men were infused with glucose (4.5mg/kgmin, 2300-0700h) and saline, respectively, during nocturnal sleep (n=9) or wakefulness (n=11). Circulating concentrations of ACTH, cortisol, glucose, insulin, and leptin were measured and food consumption in the next morning was assessed. Independent of sleep, glucose infusion reduced levels of ACTH (P<0.01) and cortisol (P<0.02) during the second night half. In the Sleep group, glucose infusion enhanced rapid eye movement (REM) sleep at the expense of sleep stage 2 (each P<0.05). Glucose infusion increased leptin levels in both groups (P<0.005) and reduced morning food intake in the Wake (P<0.02) but not in the Sleep group (P>0.46). Our findings support the view that increasing energy demands of the brain towards the end of the night essentially contribute to the early morning rise in HPA axis activity. Sleep is not critically involved in this glucose-glucocorticoid feedback loop but may reduce the brain's sensitivity to the anorexigenic effect of enhanced glucose supply.

Salivary cortisol as a biomarker in stress research

Salivary cortisol is frequently used as a biomarker of psychological stress. However, psychobiological mechanisms, which trigger the hypothalamus-pituitary-adrenal axis (HPAA) can only indirectly be assessed by salivary cortisol measures. The different instances that control HPAA reactivity (hippocampus, hypothalamus, pituitary, adrenals) and their respective modulators, receptors, or binding proteins, may all affect salivary cortisol measures. Thus, a linear relationship with measures of plasma ACTH and cortisol in blood or urine does not necessarily exist. This is particularly true under response conditions. The present paper addresses several psychological and biological variables, which may account for such dissociations, and aims to help researchers to rate the validity and psychobiological significance of salivary cortisol as an HPAA biomarker of stress in their experiments.

Dynamics of sleep stage transitions in healthy humans and patients with chronic fatigue syndrome

Physiological and/or pathological implications of the dynamics of sleep stage transitions have not, to date, been investigated. We report detailed duration and transition statistics between sleep stages in healthy subjects and in others with chronic fatigue syndrome (CFS); in addition, we also compare our data with previously published results for rats. Twenty-two healthy females and 22 female patients with CFS, characterized by complaints of unrefreshing sleep, underwent one night of polysomnographic recording. We find that duration of deep sleep (stages III and IV) follows a power-law probability distribution function; in contrast, stage II sleep durations follow a stretched exponential and stage I, and REM sleep durations follow an exponential function. These stage duration distributions show a gradually increasing departure from the exponential form with increasing depth of sleep toward a power-law type distribution for deep sleep, suggesting increasing complexity of regulation of deeper sleep stages. We also find a substantial number of REM to non-REM sleep transitions in humans, while this transition is reported to be virtually nonexistent in rats. The relative frequency of this REM to non-REM sleep transition is significantly lower in CFS patients than in controls, resulting in a significantly greater relative transition frequency of moving from both REM and stage I sleep to awake. Such an alteration in the transition pattern suggests that the normal continuation of sleep in light or REM sleep is disrupted in CFS. We conclude that dynamic transition analysis of sleep stages is useful for elucidating yet-to-be-determined human sleep regulation mechanisms with pathophysiological implications.

Dissociation of ACTH and glucocorticoids

It is increasingly clear that significant differential regulation of pituitary and adrenal gland activation exists, leading to a dissociation of plasma adrenocorticotropic hormone and corticosteroid secretion during fetal, postnatal and adult life. An increasing number of preclinical and clinical studies report dissociation of adrenocorticotropic hormone and cortisol levels in critical illness, inflammation and mental disorders. Mechanisms involve an altered adrenal sensitivity, aberrant receptor expression or modulation of adrenal function by cytokines, vasoactive factors or neuropeptides. The degree of dissociation has been associated with the level of complications of sepsis, surgery, malignant disease and depression. The separation of adrenocorticotropic hormone and corticosteroid secretion is of clinical relevance and should be incorporated into our view on endocrine stress regulation.

Exploration of basal diurnal salivary cortisol profiles in middle-aged adults: associations with sleep quality and metabolic parameters

The use of saliva samples is a practical and feasible method to explore basal diurnal cortisol profiles in free-living research. This study explores a number of psychological and physiological characteristics in relation to the observed pattern of salivary cortisol activity over a 12-h period with particular emphasis on sleep. Basal diurnal cortisol profiles were examined in a sample of 147 volunteers (mean age 46.21+/-7.18 years). Profiles were constructed for each volunteer and explored in terms of the area under the curve (AUC) of the cortisol-awakening response with samples obtained immediately upon waking (0, 15, 30 and 45 min post waking) and at 3, 6, 9 and 12h post waking to assess diurnal decline. Diurnal mean of cortisol was based on the mean of cortisol at time points 3, 6, 9 and 12h post waking. Psychological measures of perceived stress and sleep were collected with concurrent biological assessment of fasting plasma glucose, insulin, blood lipids and inflammatory markers. Blunted cortisol profiles, characterised by a reduced AUC, were observed in the majority (78%) of a middle-aged sample and were associated with significantly poorer sleep quality and significantly greater waist-hip ratio (WHR). Blunted cortisol profiles were further associated with a tendency to exhibit a less favourable metabolic profile. These findings suggest that reduced cortisol secretion post waking may serve as an additional marker of psychological and biological vulnerability to adverse health outcomes in middle-aged adults.