REM Sleep Episodes Research Articles

Heart rate dynamics during human sleep

To investigate the dynamics of heart rate in the course of sleep and to relate cardiac activity to sleep intensity, the electrocardiogram was recorded concomitantly with the polysomnogram in healthy young males. Heart rate was assessed across consecutive non-REM sleep (NREMS)-REM sleep (REMS) cycles as well as within individual episodes of NREMS and REMS. Within a sleep cycle, heart rate was lower in the NREMS episode than in the subsequent REMS episode. A global declining trend was present over successive NREMS episodes and over successive REMS episodes. A rapid increase of heart rate at the NREMS-REMS transitions was followed by a slow decline that started within the REMS episodes. Heart rate variability was higher in REMS than in NREMS and showed an increasing trend over successive REMS episodes but not over successive NREMS episodes. EEG slow-wave activity (spectral power density in the 0.75–4.5 Hz band), an intensity measure of NREMS, declined across NREMS episodes and was not correlated with heart rate. The global trends and ultradian variations of heart rate may represent sleep state-dependent modulations and circadian variations of the autonomic nervous system, which are not fully reflected in the sleep EEG.

The duration of REM sleep episodes in normal sleep

The distributions of the durations of the first 3 REM sleep episodes have been analysed using a total of 134 overnight sleep recordings from 10 subjects. From investigation of the length of uninterrupted episodes of stage REM, it is shown that arousals to stage 0/1 could play an important part in the process of REM exit, and that by the middle of the sleep period, these arousals probably occur according to a Poisson process. During the first and second REM episodes a more complex process appears to be at work, which could reflect increased pressure for slow wave sleep. These findings suggest that the duration of a REM episode is determined by a process that has a large stochastic element, which is not necessarily tied to REM entry.

Restructuring of sleep and reversal of REM-induced supraspinal hypotonia of respiratory muscles following bilateral phrenicotomy

The long-term effect of diaphragm paralysis on respiratory system function is still not clear. We monitored changes in breathing pattern and the sleep/wake cycle in a dog before and after bilateral phrenicotomy. The post-operative observation extended over 6 months. It was noted that minute ventilation increased during wakefulness and non-REM sleep in the initial 4–6 weeks (compared to pre-surgery period), but decreased during REM sleep, mainly due to inhibition of chest wall and abdominal muscles. These episodes resulted in hypoxemia and frequent arousals. Following this period, there was a restructuring of REM sleep, increasing the frequency of REM sleep and reducing the duration of each REM sleep episode. In addition, the enhanced activity of parasternal and abdominal muscles was persistently seen during REM sleep. These changes in breathing and sleep provided stable ventilation during sleep. We conclude that bilateral phrenicotomy restructures breathing and alters sleep/wake cycle to prevent nocturnal hypoxemia. The mechanisms underlying these changes may reflect plasticity in the control of breathing and REM sleep.

Cortical temperature and EEG slow-wave activity in the rat: analysis of vigilance state related changes.

Vigilance states, cortical temperature (TCRT), and electroencephalograph (EEG) slow-wave-activity (SWA, mean power density in the 0.75-4.0 Hz range) of ten rats were recorded continuously during a baseline day, and two recovery days (Recovery 1 and 2) after 24 h of sleep deprivation (SD). The short term changes of TCRT were analysed within episodes of nonrapid eye movement sleep (NREMS), REM sleep (REMS) and waking (W), and at transitions between vigilance states. SWA was analysed within NREMS episodes and at W to NREMS (WN) transitions. TCRT increased during episodes of W and REMS, and decreased during NREMS episodes. These changes were a function of episode duration, and, for W and NREMS, of TCRT at episode onset. In Recovery 1 the increase in TCRT at NREMS to REMS (NR) and NREMS to W (NW) transitions tended to be attenuated. SWA within NREMS episodes was enhanced after SD. Over all experimental days, the increase of SWA and the decrease of TCRT in NREMS episodes were not correlated. It is concluded that during recovery from SD the changes in TCRT at state transitions were little affected. The lack of a relationship between changes in TCRT and SWA indicates that separate mechanisms underlie the regulation of brain temperature and sleep intensity.

A quantitative analysis of phasic and tonic submental EMG activity in human sleep

Submental muscle activity and slow-wave activity in the EEG (mean power density in the 0.75–4.5-Hz band) were determined for consecutive 20-sec epochs in 34 all-night recordings of human sleep. Muscle activity was quantified by calculating the statistical variance of the digitized electromyogram (EMG). The tonic level of muscle activity was lower in REM sleep (REMS) than in nonREMS, and higher in the first nonREMS episode than in subsequent nonREMS episodes. The tonic EMG level exhibited a significant decreasing trend within the first nonREMS episode but an increasing trend within all subsequent nonREMS episodes. EEG slow-wave activity increased in the first part of all nonREMS episodes and decreased in the first part of all REMS episodes. The absolute or relative difference in muscle activity between two consecutive 20-sec intervals was used for defining EMG arousals. The density of arousals did not differ significantly among nonREMS episodes. Weak and moderate arousals showed an increasing density over consecutive REMS episodes. While arousals were uniformly distributed within REMS episodes, they were concentrated at the beginning and the end of nonREMS episodes.

Simulation of Human Sleep: Ultradian Dynamics of Electroencephalographic Slow-Wave Activity

The typical declining trend of electroencephalographic (EEG) slow-wave activity (SWA) within a sleep period is represented in the two-process model of sleep regulation by an exponentially decaying process (Process S). The model has been further elaborated to simulate not only the global changes of SWA, but also the dynamics within non-rapid-eye-movement (non-REM) sleep episodes. In this new model, the initial intraepisodic buildup of SWA is determined by the combined action of an exponentially increasing process and a saturation process, whereas its fall at the end of an episode is due to an exponentially decreasing process. The global declining trend of SWA over consecutive episodes results from the monotonic decay of the intraepisodic saturation level. In contrast to Process S in the two-process model, this decay is not represented by an exponential function, but is proportional to the momentary level of SWA. REM sleep episodes are triggered by an external function. The model allows one to simulate the ultradian pattern of SWA for baseline nights as well as changes induced by a prolonged waking period, a daytime nap, a partial slow-wave sleep deprivation, or an antidepressant drug.

Thermal Environment, Sleep and Energy Metabolism in Piglets

Heat production, respiratory quotient (RQ) and body temperature were measured in 1- to 9-d old piglets during the individual REM sleep episodes and compared with the respective values obtained in non-rapid-eye-movement (NREM) sleep. Two-hour measurements were carried out in· metabolic respiratory chambers under comfortable ther­ mal conditions and upon exposure to cold. Thermal comfort was provided by heating the flocr to 37°C to 38 °C for 1- to 5-d old piglets and to 34°C to 36 °c for the older animals. The air temperature in the chamber ranged between 25°C and 26 0c. Exposure· to cold was produced by decreasing the floor temperature to 28 cc. Under cold exposure the total duration of REM sleep was reduced by 50 to 60 %. Both. the number of REM sleep episodes. and their duration were decreased. Heat production in REM sleep was invariably reduced. Under exposure to cold this decrease was highly significant (P < 0.01) owing to the disappearance of muscular tremor. However, concurrent decrease in body temperature, recorded in 1- to 3-d old piglets, was not significant. In the thermoneutral environment a significant (P < 0.05) decrease in heat production was observed during REM episodes occurring shortly after food intake. By depressing the postprandial thermogenesis, REM sleep contributes apparently to more effective utilization of the food energy. Lower RQ values observed in REM sleep are related to lower glucose oxidation under muscular atony. Sleep, thermal environment, oxygen consumption, RQ

Sommeil et reves dans l'amnesie de Korsakoff d'origine alcoolique

Sleep and dreams in 15 chronic alcoholic patients with amnesia were compared with sleep and dreams of 15 age- and sex-adjusted normal subjects. The patients were subjected to psychological tests in order to determine their I.Q. and their memory disturbances. All subjects had two nights of polygraphic recordings; the first tested the natural sleep organization. During the second night, they were awakened 7 min after the onset of each REM sleep episode, and, at least once, 20 min after the onset of a stage II episode, in order to record on a tape their dream reports according to a standardized protocol. The sleep patterns of the amnesic patients did not show any significant alteration. However, after wakening during the night, patients exhibited a higher tendency to return to REMS than controls. There was still some dream activity in those patients, although noticeably less frequently, and their dream activity had a very poor verbal expression. However, there was no change with respect to the spatio-temporal organization, sensorial perceptions, motor activity and verbalizations during their dreams.

Sleep suppression following kainic acid-induced lesions of the basal forebrain

We have described elsewhere neurons in the ventral basal forebrain of cats that have elevated discharge rates during sleep and during transitions from waking to sleep, yet have comparatively low discharge rates during waking. These sleep-active neurons may mediate the hypnogenic properties of the basal forebrain. To further evaluate their role in the control of sleep, we examined the effects of basal forebrain lesions produced by microinjections of the relatively cell-selective neurotoxin, kainic acid, on sleep. Lesions were made bilaterally in two regions that contain high densities of sleep-active neurons: the horizontal limb of the diagonal bands of Broca and the lateral preoptic area-substantia innominata. Twelve-hour polygraph recordings were made before and at various intervals after basal forebrain damage in a total of eight cats. The lesions resulted in reduced time spent in deep, nonrapid eye-movement sleep and REM sleep, and increased time spent awake. These abnormalities persisted through 6 to 7 weeks postlesion. Reductions in deep non-REM sleep were due to decreases in bout number, particularly in the number of extended deep non-REM episodes (i.e., those >5 min in duration). The number of REM sleep episodes was also significantly reduced. The average duration of epochs of waking was elevated throughout the postlesion period. Thus, in the postlesion period, cats exhibited an impaired ability to initiate and maintain consolidated periods of sleep, particularly of deeper sleep stages. Lesions were also associated with reduced EEG spindling during sleep. These results are consistent with our hypothesis that sleep-active neurons are a component of a basal forebrain sleep- and EEG-regulating mechanism.

State disorders and state-dependent seizures in amygdala-kindled cats

This study replicated and extended previous work indicating a reciprocal relationship between persistent sleep disorders and seizure susceptibility in amygdala-kindled cats. Eight kindled cats (experimental group) and six nonkindled cats (control group) were assessed for several sleep and waking state parameters. Seizure susceptibility, indexed by thresholds to generalized afterdischarge and tonic-clonic convulsions, was also evaluated in experimental subjects during each of the following states: alert but quiet wakefulness, slow-wave sleep, transitions from slow-wave to REM sleep, and REM sleep. There were two primary findings; (i) slow-wave sleep and transitions from it to REM sleep were disrupted in amygdala-kindled cats whereas REM sleep was normal when an effective transition had been made; and (ii) disturbed states were also more susceptible to generalized seizures than were stable REM sleep and waking episodes, suggesting that abnormal rather than normal sleep created a predisposition for seizures.

Are REM cycles in narcoleptic patients governed by an ultradian rhythm?

Twelve narcoleptic subjects experiencing at least five daytime REM sleep episodes were monitored for 34 consecutive hours in the laboratory starting at 2200 h one evening and ending at 0800 h a day and a half later. There was no significant difference between the length of the daytime and nighttime REM cycles. To test the hypothesis that an underlying rhythm governs REM episodes, a grid was constructed on the basis of the mean and the SD of the daytime cycles (starting at 0800 h the first morning) was projected on the following nighttime and its correspondence with actual night cycles was evaluated. Overall, it was observed that the number of night cycles falling within the projected grid was significantly higher than chance (p less than 0.01), indicating that nighttime REM episodes tended to fall within the same periodicity as their preceding daytime episodes. This observation supports the hypothesis that an underlying basic rest-activity cycle governs REM sleep episodes in narcoleptic subjects.

Tremor at rest episodes in unilaterally 6-OHDA-induced substantia nigra lesioned rats: EEG-EMG and behavior

Twenty male adult Wistar rats were unilaterally lesioned in the substantia nigra (SN) with 6-hydroxydopamine (6-OHDA), and prepared with chronic cortical (ECoG) and neck muscle (EMG) electrodes. Longitudinal study over a period of up to 18 months demonstrated the emergence, in about two-thirds of the rats, of spontaneous repetitive episodes of head and neck tremor during awake at rest, of up to 20 seconds duration each, that were associated with spike and wave-like ECoG activities. These episodes of tremor at rest disappeared during sleep and REM sleep episodes, and also following the i.p. administration of L-DOPA. It is assumed that these tremor at rest episodes are analogous to those reported to occur in primates after experimentally induced dysfunction of the nigro-striatal, extrapyramidal system.

The acetylcholinesterase inhibitor di-isopropyl-fluorophosphate increases REM sleep in rats

In this experiment, rats were treated chronically with moderate doses of the acetylcholinesterase inhibitor di-isopropyl-fluorophosphate (DFP). After an initial injection of 1.0 mg/kg DFP, the rats received a 0.5 mg/kg injection every third day thereafter for a total of 5 injections (13 days). Following the treatment regimen, the rats were found to have increased amounts of REM sleep compared to vehicle control rats. The time spent awake and in slow wave sleep was relatively unaffected. The increase in REM sleep appears to be due to increased numbers of REM sleep episodes and not an increase in the average length of the REM sleep episodes. Furthermore, the increased REM sleep does not appear to be due to REM rebound or to disruptions of circadian rhythm.

Prenatal development of sleep-wake patterns in sheep.

Chronic intrauterine monitoring of electrocortical activity, eye movements, and electromyographic activity of the nuchal muscles has permitted the use of established polygraphic criteria to study the ontogenetic development of organized sleep-wake patterns in the fetal lamb in utero. Sixty-five polygraphic recordings obtained from 21 fetal lambs ranging from 112 to 144 days of gestation (term = 145 days) were analyzed. The results show that the transition from disorganized to organized behavioral state patterns occurs at approximately 115-120 days (0.8 term). The physiologic characteristics of the arousal, quiet sleep (QS), and REM sleep (REMS) states are qualitatively similar to those in the adult. There is initially a high proportion of REMS (greater than 50%), with only 11% time spent in arousal. The direct transition from arousal to REMS without a QS period is frequently seen in the fetus at all ages. Quantitative changes in the distribution of behavioral states continue throughout gestation. There is a significant decrease in the incidence of REMS, with a small increase in arousal and QS. The duration of QS and REMS episodes increases with age until a steady level is achieved by 130 days. There is also an increase in the frequency of occurrence of arousal periods, with no change in episode duration.

Spontaneous awakening from sleep in infants

Spontaneous awakenings from sleep were studied in a group of 20 infants whose sleep-waking patterns were recorded polygraphically for 24 h. While 10 infants were orally fed the other 10 underwent continuous feeding for various gastrointestinal diseases. Spontaneous awakening from sleep was analysed with regard to the prior sleep state, age and feeding condition. Infants awoke preferentially out of REM sleep and less often out of non-REM sleep. The feeding condition had no significant influence on the distribution of awakenings. The propensity for REM awakenings was significantly greater than would have been expected according to the REM sleep amount. This tendency was more pronounced for younger (≦ 3 months) than for older (≧ 4 months) infants. REM sleep episodes which were interrupted by awakenings were significantly shorter than uninterrupted ones, since awakenings occurred predominantly shortly after REM sleep onset. It is proposed that the specific pattern of brain activity during REM sleep facilitates the transition from sleep into the waking state, particularly in the youngest infants.

Spontaneous termination of ad libitum sleep episodes with special reference to REM sleep

The spontaneous terminations of 72 ad libitum sleep episodes, recorded from 9 young adults, were analysed with respect to their proximity to REM sleep periods. Sleep episodes occurred throughout the 24 h day as a result of the experimental design, in which subjects were confined to bed for 60 continuous hours. For the group, sleep terminations occurred from REM sleep significantly more often than would be expected by chance (40% of the time). However, substantial individual differences in ‘style’ of sleep termination were observed, with 4 subjects contributing 82% of all terminations from REM sleep. Such individual differences were noted also in the tendency to exhibit brief interruptions of ongoing REM episodes. Both terminations of sleep from REM and brief interruptions of REM showed a general tendency to occur prior to about halfway through a REM sleep episode. The tendency to awaken differentially from REM sleep is interpreted on the basis of REM sleep providing the optimal physiological conditions for the transition from sleep to waking.

Hypercapnia alters sleep state pattern.

Mild hypercapnia in the adult animal does not affect sleep pattern but more severe hypercapnia in the fetus increases the duration of REM sleep. Adult male rats were exposed daily for 2-3 h sessions at random to 6, 7, and 8% CO2 or room air. Breathing CO2 caused a 60% increase in sleep onset latency, a 28% decrease in sleep duration, but no change in percent time spent in REM. However, the duration of REM sleep episodes increased by 30%. Thus, in both fetal and adult animals severe hypercapnia appears to have a similar effect on sleep pattern.

REM-NREM cycle in the cat may be sleep-dependent.

The periodicity of the rapid eye movement-nonrapid eye movement (REM-NREM) cycle in real time versus compressed sleep was determined by autocorrelation, computed on the sequence of sleep stages in recordings from spontaneously sleeping cats. The resulting autocorrelation function was correlated to damped cosine waves, and the highest squared correlation coefficient (r2) was taken as indicating the most likely periodicity in the data entered for each animal. The periodicity of REM sleep was stronger (significantly higher r2) in the compressed sleep data than in the real-time data, indicating sleep dependency of the REM-NREM cycle. The REM-NREM cycle lengths determined by the autocorrelation technique were not significantly different for the real-time and compressed sleep data. The REM sleep episode interval, defined as the average interval between the start of successive REM sleep episodes, was significantly shorter for real-time sustained sleep than the cycle lengths as determined by the autocorrelation technique. A model is proposed which explains this phenomenon as due to fragmentation of REM sleep within the time periods with high probability for REM sleep. When such fragmentation occurs, the average REM sleep episode interval will not reflect an ultradian REM sleep periodicity.

Nocturnal angina and sleep

1. 1. Nocturnal sleep and electro cardiographic patterns were continously investigated in 20 male patients suffering from nocturnal angina attacks. Sleep pattern was severely disturbed regardless of the presence of ischemic episodes. Sleep Time was reduced because of a large Awakening Time and an Early Final Awakening. Stages 1 and 2 were increased and stages 3, 4 and, less markedly, REM were reduced. 2. 2. Ischemic episodes were more frequently observed between 24:00 and 04:00 without any significant relationship to the sleep stages, thus suggesting the influence of a cronobiologic factor on the distribution of ischemic attacks during the night. 3. 3. Ischemic episodes observed during the hemodynamic monitoring did not show any significant relation to the increase of myocardial oxygen consumption. This observation, together with the lack of relation between REM sleep and ischemic episodes during the night, seem to support the hypothesis of a reversible coronary spasm in the pathogenesis of nocturnal angina.

Distribution of REM Sleep on a 90 Minute Sleep-Wake Schedule

Ten young adult (ages 17-21) volunteers lived on a 90 min sleep-wake schedule for 86 (n = 5) or 96 (n = 5) consecutive 90 min periods. Subjects were permitted to sleep in 30 min episodes separated by 60 min of enforced wakefulness. These bedrest episodes were monitored by electroencephalogram, electro-oculogram, and electromyogram and were scored in 30 sec epochs using standard criteria. REM sleep episodes on this schedule occurred with a clear daily cycle; 74% of REM sleep time occurred during the rising phase of the body temperature cycle. REM showed a marked tendency to recur during alternate bedrest episodes. Finally, REM and slow wave sleep occurred together during only 27 of 910 bedrest episodes. The findings support a circadian influence on the temporal distribution of REM sleep. Neither the sleep-independent nor the sleep-dependent models of REM sleep were supported by findings on the 90 min schedule.