Proposed supplements and amendments to 'A Manual of Standardized Terminology, Techniques and Scoring System for Sleep Stages of Human Subjects', the Rechtschaffen & Kales (1968) standard

Sleep enhances explicit recollection in recognition memory

Recognition memory is considered to be supported by two different memory processes, i.e., the explicit recollection of information about a previous event and an implicit process of recognition based on an acontextual sense of familiarity. Both types of memory supposedly rely on distinct memory systems. Sleep is known to enhance the consolidation of memories, with the different sleep stages affecting different types of memory. In the present study, we used the process-dissociation procedure to compare the effects of sleep on estimates of explicit (recollection) and implicit (familiarity) memory formation on a word-list discrimination task. Subjects studied two lists of words before a 3-h retention interval of sleep or wakefulness, and recognition was tested afterward. The retention intervals were positioned either in the early night when sleep is dominated by slow-wave sleep (SWS), or in the late night, when sleep is dominated by REM sleep. Sleep enhanced explicit recognition memory, as compared with wakefulness (P < 0.05), whereas familiarity was not affected by sleep. Moreover, explicit recognition was particularly enhanced after sleep in the early-night retention interval, and especially when the words were presented with the same contextual features as during learning, i.e., in the same font (P < 0.05). The data indicate that in a task that allows separating the contribution of explicit and implicit memory, sleep particularly supports explicit memory formation. The mechanism of this effect appears to be linked to SWS.

Common scale-invariant patterns of sleep-wake transitions across mammalian species

Although mammals of different species have different sleep patterns, brief sleep-wake transitions commonly are observed across species and appear to occur randomly throughout the sleeping period. The dynamical patterns and functions of these brief awakenings from sleep are not well understood, and they often are viewed as disruptions (random or pathologic) of the sleep process. In this article, we hypothesize that brief awakenings from sleep may reflect aspects of the endogenous sleep control mechanism and thus may exhibit certain robust dynamical patterns across species. We analyze sleep recordings from mice, rats, cats, and humans, and we compare the distributions of sleep and wake episode durations. For all four species, we find that durations of brief wake episodes during the sleep period exhibit a scale-free power-law behavior with an exponent alpha that remains the same for all species (alpha approximately equal to 2.2). In contrast, sleep episode durations for all four species follow exponential distributions with characteristic time scales, which change across species in relation to body mass and metabolic rate. Our findings suggest common dynamical features of brief awakenings and sleep durations across species and may provide insights into the dynamics of the neural circuits controlling sleep.

Review article: sleep and its relationship to gastro-oesophageal reflux

Gastro-oesophageal reflux disease (GERD) is among the most common gastrointestinal conditions in the USA. For most symptomatic patients, reflux events occur during both daytime and night-time hours. Whereas daytime reflux events tend to be frequent but brief, reflux events that occur during sleep are comparatively less frequent but significantly longer. Longer oesophageal acid-clearance and acid-mucosal contact times during sleep are at least partly due to several physiological changes associated with sleep, including dramatic declines in saliva production and frequency of swallowing, decreased conscious perception of heartburn and consequent arousal and clearance behaviours, and slower gastric emptying. Obstructive sleep apnea syndrome and obesity seem to predispose some patients to nocturnal GERD, and the presence of either of these conditions may help to identify patients with symptoms consistent with GERD. Recognition and treatment of night-time GERD are important because it can be associated with decreased quality of life (including sleep disruption) and increased risk of serious oesophageal and respiratory complications.

[Snoring/sleep apnea--surgically curable]

INTRODUCTION

Obstructive sleep apnea (OSA) is characterized by nocturnal collapsing of the upper airways. Nasal continuous positive airway pressure (nCPAP) ventilation is the gold standard in the treatment of obstructive sleep apnea syndrome (OSAS). Long-term compliance rates do not exceed more than 60 to 70%. Alternative multi-level surgeries are of interest, combining procedures at the level of the base of tongue and the soft palate in order to stabilize the airway. Preliminary results suggested the hyoid suspension as one part of the multi-level surgery concept to be of high effectiveness. Therefore this study investigated the outcome of the hyoid suspension and compared it with the CPAP therapy.

METHODS

Between March 2001 and February 2003, 66 patients with OSA were treated with a hyoid suspension in combination with surgeries at the base of tongue, the soft palate or the nose (always performed by the same surgeon). All patients underwent a pre- and postoperative polysomnography in the sleep lab. Daytime sleepiness was assessed using the Epworth Sleepiness Scale (ESS). Mean age was 52,1 years, the mean body mass index (BMI) was 28,04 kg/m(2).

RESULTS

The mean apnea-hypopnea-index (AHI) was 38,9121,10/h before operation and 19,25+/-19,64/h after operation (p<0,0001). More statistically significant changes were found for the arousal index, the oxygen saturation and the ESS (p<0,05). After surgery 57,6% of the subjects (38/66) were regarded as cured (reduction of AHI > or =50% and below 15/h). Another 21,2% (14/66) improved (reduction of AHI >20%). Altogether 78,8% of the patients were counted as responders.

CONCLUSION

Multi-level surgeries based on the hyoid suspension show the effectiveness of this concept. This surgical strategy could be equal to the CPAP mask, especially in cases of CPAP intolerance.

Melatonin advances the circadian timing of EEG sleep and directly facilitates sleep without altering its duration in extended sleep opportunities in humans

The rhythm of plasma melatonin originating from the pineal gland and driven by the circadian pacemaker located in the suprachiasmatic nucleus is closely associated with the circadian (approximately 24 h) variation in sleep propensity and sleep spindle activity in humans. We investigated the contribution of melatonin to variation in sleep propensity, structure, duration and EEG activity in a protocol in which sleep was scheduled to begin during the biological day, i.e. when endogenous melatonin concentrations are low. The two 14 day trials were conducted in an environmental scheduling facility. Each trial included two circadian phase assessments, baseline sleep and nine 16 h sleep opportunities (16.00-08.00 h) in near darkness. Eight healthy male volunteers (24.4 +/- 4.4 years) without sleep complaints were recruited, and melatonin (1.5 mg) or placebo was administered at the start of the first eight 16 h sleep opportunities. During melatonin treatment, sleep in the first 8 h of the 16 h sleep opportunities was increased by 2 h. Sleep per 16 h was not significantly different and approached asymptotic values of 8.7 h in both conditions. The percentage of rapid eye movement (REM) sleep was not affected by melatonin, but the percentage of stage 2 sleep and sleep spindle activity increased, and the percentage of stage 3 sleep decreased. During the washout night, the melatonin-induced advance in sleep timing persisted, but was smaller than on the preceding treatment night and was consistent with the advance in the endogenous melatonin rhythm. These data demonstrate robust, direct sleep-facilitating and circadian effects of melatonin without concomitant changes in sleep duration, and support the use of melatonin in the treatment of sleep disorders in which the circadian melatonin rhythm is delayed relative to desired sleep time.

The role of sleep in changing our minds: a psychologist's discussion of papers on memory reactivation and consolidation in sleep

The group of papers on memory reactivation and consolidation during sleep included in this volume represents cutting edge work in both animals and humans. They support that the two types of sleep serve different necessary functions. The role of slow wave sleep (SWS) is reactivation of the hippocampal-neocortical circuits activated during a waking learning period, while REM sleep is responsible for the consolidation of this new learning into long-term memory. These studies provide further insights into mechanisms involved in brain plasticity. Robeiro has demonstrated the upregulation of an immediate-early gene (IEG zif 268) to waking levels, which occurs only in REM and only in connection with new learning. McNaughton and his group have identified electrical indicators that the hippocampus and neocortex are talking to each other by testing the coactivation of hippocampal sharp wave bursts in SWS and shifts from down to up states of activation in the neocortex. In human studies Smith's group reports work on individual differences such as intelligence and presleep alcohol that affect postsleep performance, and Stickgold and collaborators report that a short nap will improve performance if it contains REM sleep. Payne and Nadel suggest that the recall benefit associated with REM sleep may be due to its association with increased cortisol levels. These papers are important not only in their individual contributions but also in revitalizing the work coordinating waking and sleep. This promises to further the understanding of how our unique capacity to learn from experience and modify our behavior takes place.

Reverberation, storage, and postsynaptic propagation of memories during sleep

In mammals and birds, long episodes of nondreaming sleep ("slow-wave" sleep, SW) are followed by short episodes of dreaming sleep ("rapid-eye-movement" sleep, REM). Both SW and REM sleep have been shown to be important for the consolidation of newly acquired memories, but the underlying mechanisms remain elusive. Here we review electrophysiological and molecular data suggesting that SW and REM sleep play distinct and complementary roles on memory consolidation: While postacquisition neuronal reverberation depends mainly on SW sleep episodes, transcriptional events able to promote long-lasting memory storage are only triggered during ensuing REM sleep. We also discuss evidence that the wake-sleep cycle promotes a postsynaptic propagation of memory traces away from the neural sites responsible for initial encoding. Taken together, our results suggest that basic molecular and cellular mechanisms underlie the reverberation, storage, and propagation of memory traces during sleep. We propose that these three processes alone may account for several important properties of memory consolidation over time, such as deeper memory encoding within the cerebral cortex, incremental learning several nights after memory acquisition, and progressive hippocampal disengagement.

Posttraining increases in REM sleep intensity implicate REM sleep in memory processing and provide a biological marker of learning potential

Posttraining rapid eye movement (REM) sleep has been reported to be important for efficient memory consolidation. The present results demonstrate increases in the intensity of REM sleep during the night of sleep following cognitive procedural/implicit task acquisition. These REM increases manifest as increases in total number of rapid eye movements (REMs) and REM densities, whereas the actual time spent in REM sleep did not change. Further, the participants with the higher intelligence (IQ) scores showed superior task acquisition scores as well as larger posttraining increases in number of REMs and REM density. No other sleep state changes were observed. None of the pretraining baseline measures of REM sleep were correlated with either measured IQ or task performance. Posttraining increases in REM sleep intensity implicate REM sleep mechanisms in further off-line memory processing, and provide a biological marker of learning potential.

Increased deep sleep in a medication-free, detoxified female offender with schizophrenia, alcoholism and a history of attempted homicide: case report

BACKGROUND

Psychiatric sleep research has attempted to identify diagnostically sensitive and specific sleep patterns associated with particular disorders. Both schizophrenia and alcoholism are typically characterized by a severe sleep disturbance associated with decreased amounts of slow wave sleep, the physiologically significant, refreshing part of the sleep. Antisocial behaviour with severe aggression, on the contrary, has been reported to associate with increased deep sleep reflecting either specific brain pathology or a delay in the normal development of sleep patterns. The authors are not aware of previous sleep studies in patients with both schizophrenia and antisocial personality disorder.

CASE PRESENTATION

The aim of the present case-study was to characterize the sleep architecture of a violent, medication-free and detoxified female offender with schizophrenia, alcoholism and features of antisocial personality disorder using polysomnography. The controls consisted of three healthy, age-matched women with no history of physical violence. The offender's sleep architecture was otherwise very typical for patients with schizophrenia and/or alcoholism, but an extremely high amount of deep sleep was observed in her sleep recording.

CONCLUSIONS

The finding strengthens the view that severe aggression is related to an abnormal sleep pattern with increased deep sleep. The authors were able to observe this phenomenon in an antisocially behaving, violent female offender with schizophrenia and alcohol dependence, the latter disorders previously reported to be associated with low levels of slow wave sleep. New studies are, however, needed to confirm and explain this preliminary finding.

Nonlinear analysis of EEG during NREM sleep reveals changes in functional connectivity due to natural aging

The spatial organization of nonlinear interactions between different brain regions during the first NREM sleep stage is investigated. This is achieved via consideration of four bipolar electrode derivations, Fp1F3, Fp2F4, O1P3, O2P4, which are used to compare anterior and posterior interhemispheric interactions and left and right intrahemispheric interactions. Nonlinear interdependence is detected via application of a previously written algorithm, along with appropriately generated surrogate data sets. It is now well understood that the output of neural systems does not scale linearly with inputs received and, thus, the study of nonlinear interactions in EEG is crucial. This approach also offers significant advantages over standard linear techniques, in that the strength, direction, and topography of the interdependencies can all be calculated and considered. Previous research has linked delta activity during the first NREM sleep stage to performance on frontally activating tasks during waking hours. We demonstrate that nonlinear mechanisms are the driving force behind this delta activity. Furthermore, evidence is presented to suggest that the aging brain calls upon the right parietal region to assist the pre-frontal cortex. This is highlighted by statistically significant differences in the rates of interdependencies between the left pre-frontal cortex and the right parietal region when comparing younger subjects (<23 years) with older subjects (>60 years). This assistance has been observed in brain-imaging studies of sleep-deprived young adults, suggesting that similar mechanisms may play a role in the event of healthy aging. Additionally, the contribution to the delta rhythm via nonlinear mechanisms is observed to be greater in older subjects.

Learning increases human electroencephalographic coherence during subsequent slow sleep oscillations

Learning is assumed to induce specific changes in neuronal activity during sleep that serve the consolidation of newly acquired memories. To specify such changes, we measured electroencephalographic (EEG) coherence during performance on a declarative learning task (word pair associations) and subsequent sleep. Compared with a nonlearning control condition, learning performance was accompanied with a strong increase in coherence in several EEG frequency bands. During subsequent non-rapid eye movement sleep, coherence only marginally increased in a global analysis of EEG recordings. However, a striking and robust increase in learning-dependent coherence was found when analyses were performed time-locked to the occurrence of slow oscillations (<1 Hz). Specifically, the surface-positive half-waves of the slow oscillation resulting from widespread cortical depolarization were associated with distinctly enhanced coherence after learning in the slow-oscillatory, delta, slow-spindle, and gamma bands. The findings identify the depolarizing phase of the slow oscillations in humans as a time period particularly relevant for a reprocessing of memories in sleep.

Postural effects on pharyngeal protective reflex mechanisms

STUDY OBJECTIVES

Pharyngeal muscle dilators are important in obstructive sleep apnea pathogenesis because the failure of protective reflexes involving these muscles yields pharyngeal collapse. Conflicting results exist in the literature regarding the responsiveness of these muscles during stable non-rapid eye movement sleep. However, variations in posture in previous studies may have influenced these findings. We hypothesized that tongue protruder muscles are maximally responsive to negative pressure pulses during supine sleep, when posterior tongue displacement yields pharyngeal occlusion.

DESIGN

We studied all subjects in the supine and lateral postures during wakefulness and stable non-rapid eye movement sleep by measuring genioglossus and tensor palatini electromyograms during basal breathing and following negative pressure pulses.

SETTING

Upper-airway physiology laboratory of Sleep Medicine Division, Brigham and Women's Hospital.

SUBJECTS/PARTICIPANTS

17 normal subjects.

MEASUREMENTS AND RESULTS

We observed an increase in genioglossal responsiveness to negative pressure pulses in sleep as compared to wakefulness in supine subjects (3.9 percentage of maximum [%max] +/- 1.1 vs 4.4 %max +/- 1.0) but a decrease in the lateral decubitus position (4.1 %max +/- 1.0 vs 1.5 %max +/- 0.4), the interaction effect being significant. Despite this augmented reflex, collapsibility, as measured during negative pressure pulses, increased more while subjects were in the supine position as compared with the lateral decubitus position. While the interaction between wake-sleep state and position was also significant for the tensor palatini, the effect was weaker than for genioglossus, although, for tensor palatini, baseline activity was markedly reduced during non-rapid eye movement sleep as compared with wakefulness.

CONCLUSION

We conclude that body posture does have an important impact on genioglossal responsiveness to negative pressure pulses during non-rapid eye movement sleep. We speculate that this mechanism works to prevent pharyngeal occlusion when the upper airway is most vulnerable to collapse eg, during supine sleep.

The sleep slow oscillation as a traveling wave

During much of sleep, virtually all cortical neurons undergo a slow oscillation (<1 Hz) in membrane potential, cycling from a hyperpolarized state of silence to a depolarized state of intense firing. This slow oscillation is the fundamental cellular phenomenon that organizes other sleep rhythms such as spindles and slow waves. Using high-density electroencephalogram recordings in humans, we show here that each cycle of the slow oscillation is a traveling wave. Each wave originates at a definite site and travels over the scalp at an estimated speed of 1.2-7.0 m/sec. Waves originate more frequently in prefrontal-orbitofrontal regions and propagate in an anteroposterior direction. Their rate of occurrence increases progressively reaching almost once per second as sleep deepens. The pattern of origin and propagation of sleep slow oscillations is reproducible across nights and subjects and provides a blueprint of cortical excitability and connectivity. The orderly propagation of correlated activity along connected pathways may play a role in spike timing-dependent synaptic plasticity during sleep.

Using a wrist-worn device based on peripheral arterial tonometry to diagnose obstructive sleep apnea: in-laboratory and ambulatory validation

STUDY OBJECTIVES

To assess the accuracy of a wrist-worn device (Watch_PAT 100) to diagnose obstructive sleep apnea in the home.

DESIGN

Participants completed 2 overnight diagnostic studies with the test device: 1 night in the laboratory with concurrent polysomnography and 1 night in the home with only the Watch_PAT. The order of the laboratory and home study nights was random. The frequency of respiratory events on the PSG was quantified using indexes based on 2 definitions of hypopnea: the respiratory disturbance index (RDI) using American Academy of Sleep Medicine Task Force criteria for clinical research, also referred to as the Chicago criteria (RDI.C), and the Medicare guidelines (RDI.M). The Watch_PAT RDI (PAT RDI) and oxygen desaturation index (PAT ODI) were then evaluated against the polysomnography RDI.C and RDI.M, respectively, for both Watch_PAT diagnostic nights, yielding IN-LAB and HOME-LAB comparisons.

SETTING

Sleep laboratory affiliated with a tertiary-care academic medical center.

PATIENTS

30 patients referred with suspected OSA.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

The polysomnography and PAT measures were compared using the mean [2 SD] of the differences and the intra-class correlation coefficient (ICC). The receiver-operator characteristic curve was used to assess optimum sensitivity and specificity and calculate likelihood ratios. For the IN-LAB comparison, there was high concordance between RDI.C and PAT RDI (ICC = 0.88, mean difference 2.5 [18.9] events per hour); RDI.M and PAT ODI (ICC = 0.95, mean difference 1.4 [12.9] events per hour; and sleep time (ICC = 0.70, mean difference 7.0 [93.1] minutes) between the test device and PSG. For the HOME-LAB comparison, there was good concordance between RDI.C and PAT RDI (ICC = 0.72, mean difference 1.4 [30.1] events per hour) and RDI.M and PAT ODI (ICC = 0.80, mean difference 1.6 [26.4] events per hour) for the test device and PSG. Home studies were performed with no technical failures.

CONCLUSIONS

In a population of patients suspected of having obstructive sleep apnea, the Watch_PAT can quantify an ODI that compares very well with Medicare criteria for defining respiratory events and an RDI that compares favorably with Chicago criteria for defining respiratory events. The device can be used with a low failure rate for single use in the lab and home for self-administered testing.

CPAP compliance in sleep apnea patients with and without laboratory CPAP titration

Advances in auto-adjusting positive airway pressure technology for obstructive sleep apnea now permit this treatment to be initiated outside of the sleep laboratory environment, bypassing the need for laboratory-based titration studies. Thus far, little research has addressed how such developments may affect compliance to continuous positive airway pressure (CPAP). We tested the effect of laboratory CPAP exposure and technologist support in a retrospective chart review of 98 veterans with obstructive sleep apnea to determine whether patients who received standard laboratory CPAP titration complied better with CPAP than did patients who received no laboratory CPAP titration. Fifty patients underwent standard technician-attended polysomnography (PSG) with CPAP titration, and 48 patients underwent unattended PSG with no laboratory trial of CPAP (first CPAP exposure was at home). Objective CPAP compliance measures were obtained from CPAP units at follow-up visits. Attended-PSG patients wore CPAP significantly longer per night on average (5.0 hours vs 3.9 hours) and tended to wear CPAP on more nights (76.5% vs 64.2%) compared with unattended-PSG patients. These findings suggest that patients' sleep laboratory experience with CPAP and the support and education provided by sleep technologists are important factors in facilitating CPAP compliance.

Residual sleepiness after N2O sedation: a randomized control trial [ISRCTN88442975]

BACKGROUND: Nitrous oxide (N2O) provides sedation for procedures that result in constant low-intensity pain. How long do individuals remain sleepy after receiving N2O? We hypothesized that drug effects would be apparent for an hour or more. METHODS: This was a randomized, double blind controlled study. On three separate occasions, volunteers (N = 12) received 100% oxygen or 20% or 40% N2O for 30 min. Dependent measures included the multiple sleep latency test (MSLT), a Drug Effects/Liking questionnaire, visual analogue scales, and five psychomotor tests. Repeated measures analysis of variance was performed with drug and time as factors. RESULTS: During inhalation, drug effects were apparent based on the questionnaire, visual analogue scales, and psychomotor tests. Three hours after inhaling 100% oxygen or 20% N2O, subjects were sleepier than if they breathed 40% N2O. No other drug effects were apparent 1 hour after inhalation ceased. Patients did not demonstrate increased sleepiness after N2O inhalation. CONCLUSION: We found no evidence for increased sleepiness greater than 1 hour after N2O inhalation. Our study suggests that long-term effects of N2O are not significant.

Parasomnias and sleep disordered breathing in Caucasian and Hispanic children - the Tucson children's assessment of sleep apnea study

BACKGROUND

Recent studies in children have demonstrated that frequent occurrence of parasomnias is related to increased sleep disruption, mental disorders, physical harm, sleep disordered breathing, and parental duress. Although there have been several cross-sectional and clinical studies of parasomnias in children, there have been no large, population-based studies using full polysomnography to examine the association between parasomnias and sleep disordered breathing. The Tucson Children's Assessment of Sleep Apnea study is a community-based cohort study designed to investigate the prevalence and correlates of objectively measured sleep disordered breathing (SDB) in pre-adolescent children six to 11 years of age. This paper characterizes the relationships between parasomnias and SDB with its associated symptoms in these children.

METHODS

Parents completed questionnaires pertaining to their child's sleep habits. Children had various physiological measurements completed and then were connected to the Compumedics PS-2 sleep recording system for full, unattended polysomnography in the home. A total of 480 unattended home polysomnograms were completed on a sample that was 50% female, 42.3% Hispanic, and 52.9% between the ages of six and eight years.

RESULTS

Children with a Respiratory Disturbance Index of one or greater were more likely to have sleep walking (7.0% versus 2.5%, p < 0.02), sleep talking (18.3% versus 9.0%, p < 0.006), and enuresis (11.3% versus 6.3%, p < 0.08) than children with an Respiratory Disturbance Index of less than one. A higher prevalence of other sleep disturbances as well as learning problems was observed in children with parasomnia. Those with parasomnias associated with arousal were observed to have increased number of stage shifts. Small alterations in sleep architecture were found in those with enuresis.

CONCLUSIONS

In this population-based cohort study, pre-adolescent school-aged children with SDB experienced more parasomnias than those without SDB. Parasomnias were associated with a higher prevalence of other sleep disturbances and learning problems. Clinical evaluation of children with parasomnias should include consideration of SDB.

Reactive oxygen metabolites (ROMs) as an index of oxidative stress in obstructive sleep apnea patients

STUDY OBJECTIVES

Obstructive sleep apnea syndrome (OSA) is accompanied by oxygen desaturation and arousal from sleep. Free oxygen radicals are highly reactive molecules which could be produced by the OSA phenomenon of hypoxia/reoxygenation: cyclical alterations of arterial oxygen saturation with oxygen desaturation developing in response to apneas followed by resumption of oxygen saturation during hyperventilation. On the basis of these considerations, it was hypothesized that OSA may be linked to increased oxidative stress.

MATERIAL AND METHODS

Twenty-six participants gave an interview during which a physician asked them about their age, smoking habits, and symptoms such as excessive daytime sleepiness and snoring. Physical examination and polysomnography were performed during their hospitalization. Reactive oxygen metabolites (ROMs) were measured in blood samples by the diacron reactive oxygen metabolites (D-ROM) test.

RESULTS

Twenty-one out of 26 subjects had an apnea/hypopnea index greater than 5 (OSA group). The measurement of free radicals was high in OSA patients. Furthermore, ROMs values in OSA patients were linearly correlated with the apnea/hypopnea index (R = 0.426; p = 0.042). The predictive value of a positive D-ROM test is 81%.

CONCLUSIONS

ROMs were elevated in patients with OSA. When OSA was severe, similarly the value of ROMs in blood samples was enhanced, and the probable underlying mechanism for these events is the hypoxia/reoxygenation phenomenon.

Variables affecting the occurrence of gastroesophageal reflux in obstructive sleep apnea patients

A number of recent studies have suggested that apnea and/or hypopnea episodes may be in a causal relationship with nocturnal gastroesophageal reflux (GER) episodes in obstructive sleep apnea (OSA) patients. In this study, we addressed the possible factors that may affect the occurrence of reflux events in OSA patients. For this reason, we investigated respiratory and sleep parameters in OSA patients with or without nocturnal GER episodes. Nineteen patients who were referred to the sleep laboratory for suspected sleep apnea were included in the study. All subjects underwent polysomnographic evaluation simultaneously with distal and proximal esophageal pH monitoring. During the recording period, a total of 134 reflux events, 134 from distal probes and none from proximal probes, were recorded. We divided patients into two groups: (1) nocturnal GER-positive patients ( n=8; age: 41.9+/-11.9) and (2) nocturnal GER-negative patients ( n=11; age: 45.4+/-3.3). We compared demographic, respiratory and sleep parameters between the two groups. Then we analysed the time relation between GER episodes and obstructive respiratory events. The two groups were matched by age and body mass index. Sleep and respiratory parameters were not different between the two groups. In conclusion, we suggested that age, body mass index and the severity of disease in obstructive sleep apnea patients are not effective determinants of gastroesophageal reflux. There is no sufficient evidence to accept arousals and obstructive apneas as primary causes of gastroesophageal reflux and vice versa. And finally, sleep macroorganisation has no impact on the occurrence of GER in OSAS.

Lack of presaccadic positivity before rapid eye movements in human REM sleep

Differences between oculomotor control of rapid eye movements (REMs) in REM sleep and that of saccades in wakefulness were examined electrophysiologically in human adults. Fourteen healthy young volunteers participated in the study. Brain potentials were recorded from the scalp and time-locked to the onsets of saccades and REMs during a visually triggered saccade task and natural nocturnal sleep. In wakefulness, presaccadic positivity (PSP) appeared at centro-parietal sites starting about 150 ms before saccades. In REM sleep, no PSP was found but a slow negative potential (pre-REM negativity: PRN) appeared at the prefrontal sites. The findings suggest that the generation of REMs does not involve the cortical process reflected in the PSP but is associated with a different neural process reflected in the PRN.

Low acetylcholine during slow-wave sleep is critical for declarative memory consolidation

The neurotransmitter acetylcholine is considered essential for proper functioning of the hippocampus-dependent declarative memory system, and it represents a major neuropharmacological target for the treatment of memory deficits, such as those in Alzheimer's disease. During slow-wave sleep (SWS), however, declarative memory consolidation is particularly strong, while acetylcholine levels in the hippocampus drop to a minimum. Observations in rats led to the hypothesis that the low cholinergic tone during SWS is necessary for the replay of new memories in the hippocampus and their long-term storage in neocortical networks. However, this low tone should not affect nondeclarative memory systems. In this study, increasing central nervous cholinergic activation during SWS-rich sleep by posttrial infusion of 0.75 mg of the cholinesterase inhibitor physostigmine completely blocked SWS-related consolidation of declarative memories for word pairs in human subjects. The treatment did not interfere with consolidation of a nondeclarative mirror tracing task. Also, physostigmine did not alter memory consolidation during waking, when the endogenous central nervous cholinergic tone is maximal. These findings are in line with predictions that a low cholinergic tone during SWS is essential for declarative memory consolidation.

Sleep-dependent theta oscillations in the human hippocampus and neocortex

Hippocampal theta waves recorded during rapid eye movement (REM) sleep are thought to play a critical role in memory consolidation in lower mammals, but previous attempts to detect similar theta oscillations in the human hippocampus have been unsuccessful. Using subdural and depth recordings from epileptic patients, we now report the first evidence of state-dependent hippocampal theta waves (4-7 Hz) in humans. Unlike the continuous theta in rodents, however, these oscillations were consistently observed during REM sleep in short (approximately 1 sec) bursts and during transitions to wake in longer epochs. Theta waves were also observed in the basal temporal lobe and frontal cortex during transitions from sleep to wake and in quiet wakefulness but not in REM, and they were not coherent with hippocampal theta oscillations. The absence of functional coupling between neocortex and hippocampus during theta periods indicates that multiple theta generators exist in the human brain, and that they are dynamically regulated by brain state. Gamma oscillations were also present during REM theta bursts, but the fluctuations in gamma power were not associated with theta phase, pointing out another significant difference between rodent and human theta properties. Together, these findings suggest that the generation mechanisms of theta oscillations in humans might have evolved from tonic to phasic in hippocampus during REM sleep and extended from hippocampus to cortex, where they appear in certain wakefulness-related states.

The sleep-improving effects of doxepin are paralleled by a normalized plasma cortisol secretion in primary insomnia. A placebo-controlled, double-blind, randomized, cross-over study followed by an open treatment over 3 weeks

RATIONALE

In primary care, sedating antidepressants are often used for treating insomnia, although their underlying sleep-promoting mechanisms are only incompletely understood. Since enhanced evening and nocturnal plasma cortisol levels are supposed to maintain insomniac sleep complaints, a functional link between sleep and cortisol secretion in the mode of action of antidepressants in insomnia might be suspected.

OBJECTIVES

We therefore investigated the effects of the tricyclic antidepressant doxepin on nocturnal sleep and plasma cortisol concentration in ten patients (age 41.3+/-9.5 years) with chronic primary insomnia between 1700 hours and 0800 hours.

METHODS

Single infusions of placebo and 25 mg doxepin were applied following a double-blind, randomized cross-over design. Afterward, all patients received 25 mg doxepin p.o. for 3 weeks in an open-study design.

RESULTS

Both doxepin application forms improved sleep significantly and reduced mean cortisol levels from 9.0+/-1.7 microg/l (single placebo i.v.) to 7.5+/-1.6 microg/l (single doxepin i.v.) or 7.6+/-2.0 microg/l (subchronic doxepin p.o.). The duration of the quiescent period of the cortisol rhythm was significantly prolonged following both doxepin administrations compared with placebo.

CONCLUSIONS

The results implicate that the sleep-improving effects of doxepin are mediated at least in part by a normalization of hypothalamic-pituitary-adrenal axis functions. Although in some patients rebound insomnia and specific side effects must be considered, our findings give a further rationale for the use of antidepressants in the treatment of primary insomnia.

Nocturnal sleep, daytime sleepiness, and quality of life in stable patients on hemodialysis

BACKGROUND

Although considerable progress has been made in the treatment of chronic kidney disease, compromised quality of life continues to be a significant problem for patients receiving hemodialysis (HD). However, in spite of the high prevalence of sleep complaints and disorders in this population, the relationship between these problems and quality of life remains to be well characterized. Thus, we studied a sample of stable HD patients to explore relationships between quality of life and both subjective and objective measures of nocturnal sleep and daytime sleepiness

METHODS

The sample included forty-six HD patients, 24 men and 22 women, with a mean age of 51.6 (10.8) years. Subjects underwent one night of polysomnography followed the next morning by a Multiple Sleep Latency Test (MSLT), an objective measure of daytime sleepiness. Subjects also completed: 1) a brief nocturnal sleep questionnaire; 2) the Epworth Sleepiness Scale; and, 3) the Quality of Life Index (QLI, Dialysis Version) which provides an overall QLI score and four subscale scores for Health & Functioning (H&F), Social & Economic (S&E), Psychological & Spiritual (P&S), and Family (F). (The range of scores is 0 to 30 with higher scores indicating better quality of life.)

RESULTS

The mean (standard deviation; SD) of the overall QLI was 22.8 (4.0). The mean (SD) of the four subscales were as follows: H&F - 21.1 (4.7); S&E - 22.0 (4.8); P&S - 24.5 (4.4); and, F - 26.8 (3.5). H&F (rs = -0.326, p = 0.013) and F (rs = -0.248, p = 0.048) subscale scores were negatively correlated with periodic limb movement index but not other polysomnographic measures. The H&F subscale score were positively correlated with nocturnal sleep latency (rs = 0.248, p = 0.048) while the H&F (rs = 0.278, p = 0.030) and total QLI (rs = 0.263, p = 0.038) scores were positively associated with MSLT scores. Both of these latter findings indicate that higher life quality is associated with lower sleepiness levels. ESS scores were unrelated to overall QLI scores or the subscale scores. Subjective reports of difficulty falling asleep and waking up too early were significantly correlated with all four subscale scores and overall QLI. Feeling rested in the morning was positively associated with S&E, P&S, and Total QLI scores.

CONCLUSION

Selected measures of both poor nocturnal sleep and increased daytime sleepiness are associated with decreased quality of life in HD patients, underscoring the importance of recognizing and treating these patients' sleep problems.

The renin-angiotensin-aldosterone system in patients with depression compared to controls--a sleep endocrine study

BACKGROUND

Hypercortisolism as a sign of hypothamamus-pituitary-adrenocortical (HPA) axis overactivity and sleep EEG changes are frequently observed in depression. Closely related to the HPA axis is the renin-angiotensin-aldosterone system (RAAS) as 1. adrenocorticotropic hormone (ACTH) is a common stimulus for cortisol and aldosterone, 2. cortisol release is suppressed by mineralocorticoid receptor (MR) agonists 3. angiotensin II (ATII) releases CRH and vasopressin from the hypothalamus. Furthermore renin and aldosterone secretion are synchronized to the rapid eyed movement (REM)-nonREM cycle.

METHODS

Here we focus on the difference of sleep related activity of the RAAS between depressed patients and healthy controls. We studied the nocturnal plasma concentration of ACTH, cortisol, renin and aldosterone, and sleep EEG in 7 medication free patients with depression (1 male, 6 females, age: (mean +/-SD) 53.3 +/- 14.4 yr.) and 7 age matched controls (2 males, 5 females, age: 54.7 +/- 19.5 yr.). After one night of accommodation a polysomnography was performed between 23.00 h and 7.00 h. During examination nights blood samples were taken every 20 min between 23.00 h and 7.00 h. Area under the curve (AUC) for the hormones separated for the halves of the night (23.00 h to 3.00 h and 3.00 h to 7.00 h) were used for statistical analysis, with analysis of co variance being performed with age as a covariate.

RESULTS

No differences in ACTH and renin concentrations were found. For cortisol, a trend to an increase was found in the first half of the night in patients compared to controls (p < 0.06). Aldosterone was largely increased in the first (p < 0.05) and second (p < 0.01) half of the night. Cross correlations between hormone concentrations revealed that in contrast to earlier findings, which included only male subjects, in our primarily female sample, renin and aldosterone secretion were not coupled and no difference between patients and controls could be found, suggesting a gender difference in RAAS regulation. No difference in conventional sleep EEG parameters were found in our sample.

CONCLUSION

Hyperaldosteronism could be a sensitive marker for depression. Further our findings point to an altered renal mineralocorticoid sensitivity in patients with depression.

The effects of self-awakening on heart rate activity in a short afternoon nap

OBJECTIVES

This study examined whether anticipatory changes exist in heart rate prior to awakening from a nap by means of self-awakening. The effects of self-awakening on sleepiness after the short nap were also studied.

METHOD

Nine students participated in 3 experimental conditions: (1) the control condition, in which participants watched television instead of taking a short nap; (2) the self-awakening condition, in which participants tried to wake up approximately 15 min after 'lights off' (criterion range: 15+/-5 min) and (3) the forced-awakening condition, in which participants were instructed to sleep for 30 min, but were awoken by the experimenter after 15 min.

RESULTS

In the self-awakening condition, heart rate gradually increased approximately 3 min before awakening. The error response ratio of the auditory-oddball task and the duration of doze time during the task were less after both types of nap conditions than in the control condition. Subjective sleepiness, which is measured after awakening, was lowest in the self-awakening condition.

CONCLUSIONS

The results of this experiment suggest that self-awakening prepares autonomic activation that facilitates a more smooth transition from sleep to awakening, and reduces sleepiness after naps.

Quality of life in nonorganic and organic sleep disorders: II. Correlation with objective and subjective quality of sleep and awakening

OBJECTIVE

The purpose of this study of 100 patients suffering from sleep-disorders was to determine correlations between their subjective health-related quality of life (HRQoL) and objective variables in sleep initiation and maintenance, sleep architecture, objective quality of awakening, psychophysiological parameters and subjective quality of sleep and awakening.

METHODS

Objective measurements were obtained from overnight diagnostic polysomnography. Subjective HRQoL was determined from the Quality of Life Index (QLI, Mezzich and Cohen) completed prior to the adaptation night. Other measurements included subjective and objective quality of sleep and awakening (psychometry) the evening before and morning after polysomnographic investigations.

RESULTS

63% of the patients were suffering from nonorganic and 37% from organic sleep disorders (SDs). Within the first group, nonorganic insomnia predominated; within the second, sleep apnea. Subjective HRQoL correlated well with subjective sleep and awakening quality, especially in nonorganic SDs. There were only a few correlations of objective measurements with subjective HRQoL: in the total group of SD patients HRQoL correlated with sleep stage S2, and in nonorganic SDs with attention scores and psychophysiological measurements (mainly the pulse rate in the evening and morning).

CONCLUSION

Our findings suggest only a weak relationship between objective sleep variables and subjective HRQoL in both organic and nonorganic SDs. However, we found various significant correlations of HRQoL with subjective measurements of sleep, especially in nonorganic SDs.

Quality of life in nonorganic and organic sleep disorders: I. Comparison with normative data

Subjective health-related quality of life (HRQoL) was investigated in 100 patients with disturbed sleep (39 women aged 52 +/- 13 years and 61 men aged 53 +/- 10 years) referred to the sleep laboratory and compared with HRQoL in 100 normal healthy adults. Measurements included the Quality of Life Index (QLI) (Mezzich and Cohen), and objective (polysomnographic) and subjective (psychometric) quality of sleep and awakening. Statistical analysis (Mann-Whitney U-test) showed HRQoL to be significantly reduced in sleep disorders (SDs), with a more pronounced reduction in nonorganic than in organic SDs. Patients with nonorganic hypersomnia were more disturbed than those with nonorganic insomnia. Within organic SDs, patients with apnea were more disturbed than those with obstructive snoring. Out of ten elementary HRQoL components, seven were disturbed in SDs: physical well-being, psychological well-being, self-care and independent functioning, occupational functioning, interpersonal functioning, personal fulfillment, and overall quality of life. No differences between patients and normal healthy subjects where found in the components social support, community and services support or spiritual fulfillment. Patients suffering from nonorganic SDs had significantly worse scores in physical and psychological well-being and overall quality of life than those with organic SDs. Patients with both SDs and additional diagnoses of affective disorders had more profoundly reduced HRQoL than those with anxiety disorders. Follow-up of 51 patients (31 with nonorganic SDs and 20 with organic SDs) one year after sleep laboratory investigation and subsequent treatment found significantly improved HRQoL compared with pre-treatment. Moreover, patients diagnosed and treated in the sleep laboratory showed lower re-hospitalization rats.

Early postnatal development of sensory gating

Sensory gating represents the nervous system's ability to inhibit responding to irrelevant environmental stimuli. In order to characterize the early development of acoustic sensory gating, suppression of auditory evoked potential component P1 (i.e. P50) in response to paired clicks was measured during REM sleep in healthy infants (1-4 months) that were without genetic risk for disrupted sensory gating function (i.e. having a relative with schizophrenia). As a group, the subjects exhibited significant response suppression. A correlation between increasing age and stronger response suppression was uncovered, even within this restricted age range. Parallel changes in sleep physiology could not be ruled out as the explanation for this change. Nevertheless, these results demonstrate that the neural circuits underlying sensory gating are functional very early in postnatal development.

Nasal continuous positive airway pressure improves quality of life in obesity hypoventilation syndrome

We studied the quality of life of obesity hypoventilation syndrome (OHS) by comparing it with age- and body mass index-matched patients without hypoventilation and age-matched obstructive sleep apnea (OSA) patients with body mass index (BMI) under 30, and the efficacy of nasal continuous positive airway pressure (CPAP) therapy for 3 to 6 months on the quality of life in these patients. Prospectively recruited patients from six sleep laboratories in Japan were administered assessments of the general health status by the Short-Form 36 Health Survey (SF-36) and subjective sleepiness by the Epworth Sleepiness Scale (ESS). Compared with matched healthy subjects, OHS and OSA patients not yet treated had worse results on the ESS scores and the SF-36 subscales for physical functioning, role limitations due to physical problems, general health perception, energy/vitality, role limitations due to emotional problems, and social functioning. The ESS scores of OHS patients were worse than those of the OSA groups including the age- and BMI-matched OSA patients. In the SF-36 subscales of OHS patients, only the subscale of social functioning showed worse results compared with that of BMI-matched OSA patients. After 3 to 6 months of treatment, ESS scores and these SF-36 subscales in all three patient groups improved to the normal level. These results suggested that the quality of life of OHS before nasal CPAP was significantly impaired and that nasal CPAP for OHS improved the quality of life associated with the improvement of daytime sleepiness to the level of the other OSA patients.

Changes in depressive symptoms after continuous positive airway pressure treatment for obstructive sleep apnea

It is generally believed that obstructive sleep apnea (OSA) causes depression in some patients, yet it is unknown whether this depression is an actual clinical phenomenon or purely a result of overlapping somatic/physical symptoms shared by both disorders. The present study investigated changes in both somatic and affective/cognitive symptoms of depression associated with the introduction of continuous positive airway pressure (CPAP) treatment for OSA. Participants were 39 outpatients (35 males, 4 females) with no current or past mental health problems, diagnosed with OSA in a hospital sleep disorders clinic. The Beck Depression Inventory (BDI) was administered prior to treatment and again 3 months after CPAP. Total BDI scores improved after CPAP, independent of objectively monitored CPAP compliance rates. Both somatic and affective/ cognitive symptoms of depression improved in a similar manner after treatment. Our findings suggest that depressive symptoms experienced by OSA patients are not solely the result of physical OSA symptoms but include a mood component as well. We introduce a hypothetical model to conceptualize the relationship between OSA and depression.

Grouping of spindle activity during slow oscillations in human non-rapid eye movement sleep

Based on findings primarily in cats, the grouping of spindle activity and fast brain oscillations by slow oscillations during slow-wave sleep (SWS) has been proposed to represent an essential feature in the processing of memories during sleep. We examined whether a comparable grouping of spindle and fast activity coinciding with slow oscillations can be found in human SWS. For negative and positive half-waves of slow oscillations (dominant frequency, 0.7-0.8 Hz) identified during SWS in humans (n = 13), wave-triggered averages of root mean square (rms) activity in the theta (4-8 Hz), alpha (8-12 Hz), spindle (12-15 Hz), and beta (15-25 Hz) range were formed. Slow positive half-waves were linked to a pronounced and microV (23.4%; p < 0.001, with reference to baseline) at the midline central electrode (Cz). In contrast, spindle activity was suppressed during slow negative half-waves, on average by -0.65 +/- 0.06 microV at Cz (-22%; p < 0.001). An increase in spindle activity 400-500 msec after negative half-waves was more than twofold the increase during slow positive half-waves (p < 0.001). A similar although less pronounced dynamic was observed for beta activity, but not for alpha and theta frequencies. Discrete spindles identified during stages 2 and 3 of non-rapid eye movement (REM) sleep coincided with a discrete slow positive half-wave-like potential preceded by a pronounced negative half-wave (p < 0.01). These results provide the first evidence in humans of grouping of spindle and beta activity during slow oscillations. They support the concept that phases of cortical depolarization during slow oscillations, reflected by surface-positive (depth-negative) field potentials, drive the thalamocortical spindle activity. The drive is particularly strong during cortical depolarization, expressed as surface-positive field potentials.

The efficacy of a mandibular advancement splint in relation to cephalometric variables

The efficacy of a titratable mandibular advancement splint (MAS) for the management of obstructive sleep apnea (OSA) was investigated in relation to supine cephalometric variables. Fourteen adults with diagnosed OSA were recruited following an initial polysomnogram. Supine cephalographic radiographs were taken at baseline and subjects wore the MAS nightly for 6 to 8 weeks. The polysomnogram and cephalogram were repeated with the MAS at maximal titration. The MAS resulted in complete or partial treatment response in all subjects as measured by the improvement in mean apnea/hypopnea index (AHI) (baseline AHI 34 +/- 22/hr, with MAS 10 +/- 5/hr; p = 0.001). The perpendicular distance between the hyoid bone and the mandibular plane (HYML) measured in awake subjects decreased with the MAS (baseline HYML 25.3 +/- 7.8 mm, with MAS 16.5 +/- 9.6 mm; p = 0.002). Baseline HYML was the only cephalometric variable associated with a successful clinical outcome. It was strongly linked to improvements in AHI (adjusted R(2) = 0.37, p = 0.012) and arousals (adjusted R(2) = 0.455, p = 0.005). We conclude that the MAS is an effective therapy for OSA and baseline HYML is an important predictor of improvement. Improvements in AHI may be explained by the MAS maintaining the new or existing relationship of the hyoid and its surrounding structures, thus preventing obstruction in the upper airway during sleep.

Sleep forms memory for finger skills

Practicing a motor skill triggers a process of memory consolidation that continues for hours after practice has ended, and becomes manifest in an improved skill at later testing. We used a sequential motor task (finger-to-thumb opposition task) to show that, in humans, the formation of motor skill memories essentially benefits from sleep. Independent of whether placed during daytime or nighttime, sleep after practice enhanced speed of sequence performance on average by 33.5% and reduced error rate by 30.1% as compared with corresponding intervals of wakefulness. The effect of sleep after learning proved to be stable when retesting was postponed for another night, to exclude effects of sleep loss and to assure that all subjects had sufficient sleep before retrieval testing. Also, the consolidating effect of sleep was specific for the motor sequence learned. It did not generalize to a similar sequence containing identical movement segments in a different order. Retention periods of wakefulness improved performance only moderately and only if placed during daytime. The observations demonstrate a critical role of sleep for storing and optimizing motor skills.

Learning-dependent increases in sleep spindle density

Declarative memory consolidation is enhanced by sleep. In the investigation of underlying mechanisms, mainly rapid eye movement (REM) sleep and slow-wave sleep have been considered. More recently, sleep stage 2 with sleep spindles as a most prominent feature has received increasing attention. Specifically, in rats hippocampal ripples were found to occur in temporal proximity to cortical sleep spindles, indicating an information transfer between the hippocampus and neocortex, which is supposed to underlie the consolidation of declarative memories during sleep. This study in humans looks at the changes in EEG activity during nocturnal sleep after extensive training on a declarative learning task, as compared with a nonlearning control task of equal visual stimulation and subjectively rated cognitive strain. Time spent in each sleep stage, spindle density, and EEG power spectra for 28 electrode locations were determined. During sleep after training, the density of sleep spindles was significantly higher after the learning task as compared with the nonlearning control task. This effect was largest during the first 90 min of sleep (p < 0.01). Additionally, spindle density was correlated to recall performance both before and after sleep (r = 0.56; p < 0.05). Power spectra and time spent in sleep stages did not differ between learning and nonlearning conditions. Results indicate that spindle activity during non-REM sleep is sensitive to previous learning experience.

Stages of sleep after psychoemotional tension: the individual character of changes

This report describes complex psychophysiological studies of nocturnal sleep in healthy humans in normal concentrations and after emotional tension. A series of contemporary methods was used: questionnaires, psychological tests, motor tests, and polysomnography with heart rate recording. These experiments showed that psychoemotional tension induced changes mainly in the structure of the first sleep cycle, decreasing the proportion of the second stage of slow sleep in total nocturnal sleep, led to a redistribution of delta sleep, increasing delta sleep in the second half of nocturnal sleep, and suppressed the mechanisms underlying the organization of the phases of rapid sleep. Psychoemotional tension affected human cerebrovisceral functions, for example inducing increases in the frequency and variability of the heart rhythm during nocturnal sleep. The nature of these changes in sleep structure and autonomic responses depended on the personality characteristics of the individual person. Thus, the individual approach to the question of psychoemotional stress in sleep disturbances is, we believe, the most appropriate.

Sleep states differentiate single neuron activity recorded from human epileptic hippocampus, entorhinal cortex, and subiculum

Animal models of epilepsy have shown that synchronous burst firing is associated with epileptogenesis, yet the evidence from human studies linking neuronal synchrony and burst firing to epileptogenesis remains equivocal. Sleep-wake states have been shown to differentially modulate the generation of epileptiform EEG spikes between brain regions of greater and lesser seizure-generating potential, providing information that helps to identify the primary epileptogenic region. Using these state-dependent mechanisms to assist us in identifying neuronal correlates of human epilepsy, we recorded interictal neuronal activity from mesial temporal lobe (MTL) areas in epileptic patients implanted with depth electrodes required for medical diagnosis during polysomnographically defined sleep-wake states. Results show that single neurons recorded ipsilateral to seizure-initiating MTL ("epileptic") areas had significantly higher firing rates (p = 0.01) and burst propensity (p = 0.01) and greater synchrony of discharges (p = 0.003) compared with neurons recorded from contralateral non-seizure-generating MTL ("non-epileptic") areas. In particular, during episodes of slow wave sleep (SWS) and rapid eye movement (REM) sleep, epileptic hippocampal neurons had significantly higher burst rates compared with non-epileptic hippocampal neurons (both p = 0.01). In contrast, during episodes of wakefulness (Aw), no difference in burst firing between epileptic and non-epileptic hippocampal neurons was observed. Furthermore, synchronous firing was significantly higher between epileptic MTL neurons compared with non-epileptic MTL neurons during SWS (p = 0.04) and REM sleep (p = 0.02), but no difference in neuronal synchrony was found between epileptic and non-epileptic neurons during Aw. These results provide evidence that sleep states differentially modulate abnormal epileptogenic neuronal discharge properties within human MTL and confirm that neuronal burst firing and enhanced neuronal synchrony observed in experimental animal models of epilepsy characterizes human epilepsy as well.

Effects of prolonged waking-auditory stimulation on electroencephalogram synchronization and cortical coherence during subsequent slow-wave sleep

Evidence suggests that sleep homeostasis is not only dependent on duration of previous wakefulness but also on experience- and/or use-dependent processes. Such homeostatic mechanisms are reflected by selective increases in the duration of a sleep stage, modifications to electrophysiological-metabolic brain patterns in specific sleep states, and/or reactivation to neuronal ensembles in subsequent sleep periods. Use-dependent sleep changes, apparently different from those changes caused by memory consolidation processes, are thought to reflect neuronal restoration processes after the sustained exposure to stimulation during the preceding wakefulness. In the present study, we investigated changes in the brain electrical activity pattern during human sleep after 6 hr of continuous auditory stimulation during previous wakefulness. Poststimulation nights showed a widespread increase of spectral power within the alpha (8-12 Hz) and sleep spindle (12-15 Hz) frequency range during slow-wave sleep (SWS) compared with the baseline night. This effect was mainly attributable to an enhanced EEG amplitude rather than an increase of oscillations, except for temporal (within alpha and sleep spindles) and parietal regions (within sleep spindles) in which both parameters contributed equally to the increase of spectral energy. Power increments were accompanied by a strengthening of the coherence between fronto-temporal cortical regions within a broad frequency range during SWS but to the detriment of the coherence between temporal and parieto-occipital areas, suggesting underlying compensatory mechanisms between temporal and other cortical regions. In both cases, coherence was built up progressively across the night, although no changes were observed within each SWS period. No electrophysiological changes were found in rapid eye movement sleep. These results point to SWS as a critical brain period for correcting the cortical synaptic imbalance produced by the predominant use of specific neuronal populations during the preceding wakefulness, as well as for synaptic reorganization after prolonged exposure to a novel sensory experience.

The characteristics of five patients with obstructive sleep apnea whose apnea-hypopnea index deteriorated after uvulopalatopharyngoplasty

The objective of this retrospective, consecutive, case series design study was to determine the number of unselected patients with obstructive sleep apnea (OSA) who deteriorated after uvulopalatopharyngoplasty (UPPP). Sixteen of 27 patients at the Sleep Clinic at Veterans Affairs Medical Center who underwent UPPP for OSA and who completed both a pre- and postpolysomnogram were studied. After comparing the apnea-hypopnea index (AHI) before and after UPPP, three groups of patients were identified: deteriorators, unchanged, and improvers. In five patients (31%), the AHI increased by more than 10% after UPPP (deteriorators); in four (25%), the AHI showed a change in either direction of less than 10% (unchanged); and in the remaining seven (44%), the AHI decreased by more than 10% after UPPP (improvers). The AHI deteriorated in five of 16 (31%) unselected patients with OSA in our clinic population who underwent UPPP. The mean pre-UPPP AHI was lower in the patients who deteriorated relative to all other patients (P = 0.02). We suggest that patients who undergo UPPP should have a post-UPPP polysomnogram to determine whether they have improved or deteriorated after the procedure and that alternative forms of treatment may be needed in some patients.

Improvement of CPAP Therapy by a Self-Adjusting System

The first generation of Auto CPAP devices caused respiratory arousal by apnoes, hypopnoeas, incomplete obstructions and pressurechanges. The new, second generation of CPAP devices which is based on forced oscillation technique will change the pressure with slower velocity and before the respiratory arousal reaction will occur (1, 9, 10). Fifty patients with severe sleep apnoea (AHI 66+/-26 /h) were treated with both, constant- CPAP (continous positive airway pressure) or Auto CPAP under polysomnographic control in a randomised order. The Auto CPAP based on forced oscillation technique reduced the number of apnoeas and hypopnoeas as did most of the other Auto CPAP systems to AHI 2.5+/-5.9 /h (p<0.05). In comparison to Auto CPAP of the first generation it also decreased the number of respiratory arousal reactions caused by apnoeas and hypopnoeas. However there is still a significant difference to number of arousal detected with constant CPAP (p<0.01). In conclusion although the new generation of Auto CPAP reduced the number of respiratory arousals compared to first generation, we did not find a therapeutical benefit for patients with severe SAS.

Effects of melatonin administration on daytime sleep after simulated night shift work

Disturbed sleep and on-the-job sleepiness are widespread problems among night shift workers. The pineal hormone melatonin may prove to be a useful treatment because it has both sleep-promoting and circadian phase-shifting effects. This study was designed to isolate melatonin's sleep-promoting effects, and to determine whether melatonin could improve daytime sleep and thus improve night time alertness and performance during the night shift. The study utilized a placebo-controlled, double-blind, cross-over design. Subjects (n=21, mean age=27.0 +/- 5.0 years) participated in two 6-day laboratory sessions. Each session included one adaptation night, two baseline nights, two consecutive 8-h night shifts followed by 8-h daytime sleep episodes and one recovery night. Subjects took 1.8 mg sustained-release melatonin 0.5 h before the two daytime sleep episodes during one session, and placebo before the daytime sleep episodes during the other session. Sleep was recorded using polysomnography. Sleepiness, performance, and mood during the night shifts were evaluated using the multiple sleep latency test (MSLT) and a computerized neurobehavioral testing battery. Melatonin prevented the decrease in sleep time during daytime sleep relative to baseline, but only on the first day of melatonin administration. Melatonin increased sleep time more in subjects who demonstrated difficulty in sleeping during the day. Melatonin had no effect on alertness on the MSLT, or performance and mood during the night shift. There were no hangover effects from melatonin administration. These findings suggest that although melatonin can help night workers obtain more sleep during the day, they are still likely to face difficulties working at night because of circadian rhythm misalignment. The possibility of tolerance to the sleep-promoting effects of melatonin across more than 1 day needs further investigation.

Misinterpretation of sleep-breathing disorder by periodic limb movement disorder

We report a case of misinterpretation of sleep-disordered breathing due to periodic limb movement disorder. A 67-year-old man was diagnosed with sleep-disordered breathing and subsequently placed on treatment with nasal continuous positive airway pressure (CPAP). The initial diagnostic evaluation did not include measurement of anterior tibialis electromyogram. The respiratory disturbance index of the initial evaluation was 23. After a brief period of nasal CPAP use, the patient discontinued the treatment because no significant change in daytime alertness was noted and signs of CPAP-related insomnia appeared. The patient was restudied polysomnographically with monitoring of anterior tibialis electromyograms. This study identified 392 leg movements of which 65% were associated with brief EEG arousal from sleep. Double-blind analysis of respiratory disturbance and leg movements yielded a total number of 360 arousals in the overnight recording. Eighty-five percent of all respiratory events could be associated with central hypoventilation following periodic limb movement-associated EEG arousal. No significant hypoxia was recorded with these events. We hypothesize that chemoreceptor stimulation secondary to EEG arousal during sleep is responsible for this central hypoventilation. This case report highlights that recording and scoring of leg movements must be an integral part of polysomnographic evaluations.

Effect of hypoxia on the hypopnoeic and apnoeic threshold for CO(2) in sleeping humans

1. Rhythmic breathing during sleep requires that P(CO2) be maintained above a sensitive hypocapnic apnoeic threshold. Hypoxia causes periodic breathing during sleep that can be prevented or eliminated with supplemental CO(2). The purpose of this study was to determine the effect of hypoxia in changing the difference between the eupnoeic P(CO2) and the P(CO2) required to produce hypopnoea or apnoea (hypopnoea/apnoeic threshold) in sleeping humans. 2. The effect of hypoxia on eupnoeic end-tidal partial pressure of CO(2) (P(ET,CO2)) and hypopnoea/apnoeic threshold P(ET,CO2) was examined in seven healthy, sleeping human subjects. A bilevel pressure support ventilator in a spontaneous mode was used to reduce P(ET,CO2) in small decrements by increasing the inspiratory pressure level by 2 cmH2O every 2 min until hypopnoea (failure to trigger the ventilator) or apnoea (no breathing effort) occurred. Multiple trials were performed during both normoxia and hypoxia (arterial O(2) saturation, S(a,O2) = 80 %) in a random order. The hypopnoea/apnoeic threshold was determined by averaging P(ET,CO2) of the last three breaths prior to each hypopnoea or apnoea. 3. Hypopnoeas and apnoeas were induced in all subjects during both normoxia and hypoxia. Hypoxia reduced the eupnoeic P(ET,CO2) compared to normoxia (42.4 +/- 1.3 vs. 45.0 +/- 1.1 mmHg, P < 0.001). However, no change was observed in either the hypopnoeic threshold P(ET,CO2) (42.1 +/- 1.4 vs. 43.0 +/- 1.2 mmHg, P > 0.05) or the apnoeic threshold P(ET,CO2) (41.3 +/- 1.2 vs. 41.6 +/- 1.0 mmHg, P > 0.05). Thus, the difference in P(ET,CO2) between the eupnoeic and threshold levels was much smaller during hypoxia than during normoxia (-0.2 +/- 0.2 vs. -2.0 +/- 0.3 mmHg, P < 0.01 for the hypopnoea threshold and -1.1 +/- 0.2 vs. -3.4 +/- 0.3 mmHg, P < 0.01 for the apnoeic threshold). We concluded that hypoxia causes a narrowing of the difference between the baseline P(ET,CO2) and the hypopnoea/apnoeic threshold P(ET,CO2), which could increase the likelihood of ventilatory instability.

Upper-airway collapsibility: measurements and sleep effects

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is characterized by repetitive pharyngeal collapse during sleep. Several techniques have been proposed to assess the collapsibility of the upper airway in awake humans, but sleep-wake comparisons have rarely been attempted and there are few studies comparing OSA patients to control subjects. We sought to compare two collapsibility measurement techniques between normal and apneic subjects, and between wakefulness and sleep.

DESIGN

We conducted three studies. First, we examined whether collapsibility assessed by negative pressure pulses (NPPs) during wakefulness reflected values during sleep in 21 normal subjects. Second, we determined in these normal subjects whether collapsibility during sleep assessed by NPPs was predictive of collapsibility measured by inspiratory resistive loading (IRL). Finally, we compared upper-airway collapsibility between apnea patients (n = 22) and normal volunteers (n = 38) during wakefulness by NPPs.

SETTING

Clinical and research laboratories at the Brigham and Women's Hospital.

PARTICIPANTS

Two populations of normal subjects (n = 21 and n = 38) and OSA patients (n = 22).

MEASUREMENTS AND RESULTS

Collapsibility during wakefulness, as measured by NPPs, correlated significantly with collapsibility during sleep (r = 0.62; p = 0.003). There was also a significant correlation between the two measures of collapsibility (IRL and NPP) during sleep (r = 0.53; p = 0.04). Both measures revealed a significant increase in pharyngeal collapsibility during sleep as compared to wakefulness. Finally, apnea patients had significantly greater pharyngeal collapsibility than control subjects during wakefulness (p = 0.017).

CONCLUSIONS

These data suggest that upper-airway collapsibility measured during wakefulness does provide useful physiologic information about pharyngeal mechanics during sleep and demonstrates clear differences between individuals with and without sleep apnea.

Insomnia, self-medication, and relapse to alcoholism

OBJECTIVE

This study was an investigation of the frequencies of insomnia and its self-medication with alcohol in a group of alcoholic patients, as well as the relationship of these variables to alcoholic relapse.

METHOD

The subjects were 172 men and women receiving treatment for alcohol dependence. They completed a sleep questionnaire, measures of alcohol problem severity and depression severity, and polysomnography after at least 2 weeks of abstinence.

RESULTS

On the basis of eight items from the Sleep Disorders Questionnaire, 61% of the subjects were classified as having symptomatic insomnia during the 6 months before treatment entry. Compared to patients without insomnia, patients with insomnia were more likely to report frequent alcohol use for sleep (55% versus 28%), had significantly worse polysomnographic measures of sleep continuity, and had more severe alcohol dependence and depression. Among 74 alcoholics who were followed a mean of 5 months after treatment, 60% with baseline insomnia versus 30% without baseline insomnia relapsed to any use of alcohol, a significant difference. Insomnia remained a robust predictor of relapse after application of logistic regression analysis to control for other variables. A history of self-medicating insomnia with alcohol did not significantly predict subsequent relapse.

CONCLUSIONS

The majority of alcoholic patients entering treatment reported insomnia symptoms. Given the potential link between insomnia and relapse, routine questions about sleep in clinical and research settings are warranted.

Emotional memory formation is enhanced across sleep intervals with high amounts of rapid eye movement sleep

Recent studies indicated a selective activation during rapid eye movement (REM) sleep of the amygdala known to play a decisive role in the processing of emotional stimuli. This study compared memory retention of emotional versus neutral text material over intervals covering either early sleep known to be dominated by nonREM slow wave sleep (SWS) or late sleep, in which REM sleep is dominant. Two groups of men were tested across 3-h periods of early and late sleep (sleep group) or corresponding retention intervals filled with wakefulness (wake group). Sleep was recorded polysomnographically. Cortisol concentrations in saliva were monitored at acquisition and retrieval testing. As expected, the amount of REM sleep was about three times greater during late than during early retention sleep, whereas a reversed pattern was observed for SWS distribution (P < 0.001). Sleep improved retention, compared with the effects of wake intervals (P < 0.02). However, this effect was substantial only in the late night (P < 0.005), during which retention was generally worse than during the early night (P < 0.02). Late sleep particularly enhanced memory for emotional texts. This effect was highly significant in comparison with memory for neutral texts (P < 0.01) and in comparison with memory after late and early wake intervals (P < 0.001). Cortisol concentration differed between early and late retention intervals but not between sleep and wake conditions. Results are consonant with a supportive function of REM sleep predominating late sleep for the formation of emotional memory in humans.

An endogenous circadian rhythm of respiratory control in humans

Many physiological and behavioural functions have circadian rhythms - endogenous oscillations with a period of approximately 24 h that can occur even in the absence of sleep. We determined whether there is an endogenous circadian rhythm in breathing, metabolism and ventilatory chemosensitivity in humans. Ten healthy, adult males were studied throughout 4 days in a stable laboratory environment. After two initial baseline days (16 h wakefulness plus 8 h sleep) that served to achieve a steady state, subjects were studied under constant behavioural and environmental conditions throughout 41 h of wakefulness. Ventilation, metabolism and the magnitude of the hypercapnic ventilatory response (HCVR) were measured every 2 h. Individuals' data were aligned according to circadian phase (core body temperature minimum; CBTmin) and averaged. In the group average data, there was a significant and large amplitude circadian variation in HCVR slope (average of +/-0.4 l min-1 mmHg-1; corresponding to +/-12.1 % of 24 h mean), and a smaller amplitude rhythm in the HCVR x-axis intercept (average of +/-1.1 mmHg; +/-2.1 % of 24 h mean). Despite a significant circadian variation in metabolism (+/-3.2 % of 24 h mean), there were no detectable rhythms in tidal volume, respiratory frequency or ventilation. This small discrepancy between metabolism and ventilation led to a small but significant circadian variation in end-tidal PCO2 (PET,CO2; +/-0.6 mmHg; +/-1.5 % of 24 h mean). The circadian minima of the group-averaged respiratory variables occurred 6-8 h earlier than CBTmin, suggesting that endogenous changes in CBT across the circadian cycle have less of an effect on respiration than equivalent experimentally induced changes in CBT. Throughout these circadian changes, there were no correlations between HCVR parameters (slope or x-axis intercept) and either resting ventilation or resting PET,CO2. This suggests that ventilation and PET,CO2 are little influenced by central chemosensory respiratory control in awake humans even when at rest under constant environmental and behavioural conditions. The characteristic change in PET,CO2 during non-rapid eye movement sleep was shown to be independent of circadian variations in PET,CO2, and probably reflects a change from predominantly behavioural to predominantly chemosensory respiratory control. This study has documented the existence and magnitude of circadian variations in respiration and respiratory control in awake humans for the first time under constant behavioural and environmental conditions. These results provide unique insights into respiratory control in awake humans, and highlight the importance of considering the phase of the circadian cycle in studies of respiratory control.