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.     

The reliability of nocturnal vaginal blood flow

Fourteen subjects participated in a sleep study designed to document the reliability of measurements of REM-related vaginal blood-flow changes. Several standard sleep parameters were also examined for comparison with vaginal measures. The most reliable vaginal measure was the maximal change in disengorgement for a given REM period averaged across a night of REM periods. The reliability of this measure compared favorably with that of a highly reliable computerized measure of REM density. It is suggested that nocturnal vaginal blood-flow measures have sufficient reliability to be useful in the differential diagnosis of organic and psychogenic sexual dysfunction.This study was supported in part by a training grant to the Department of Clinical Psychology, University of Florida, Gainesville (USPHS532DE07133-02), and a grant from the NIH (USPHSCA26364R073241-29) to the second author.     

Memory consolidation during sleep: interactive effects of sleep stages and HPA regulation

Sleep is critically involved in the consolidation of previously acquired memory traces. However, nocturnal sleep is not uniform but is subject to distinct changes in electrophysiological and neuroendocrine activity. Specifically, the first half of the night is dominated by slow wave sleep (SWS), whereas rapid eye movement (REM) sleep prevails in the second half. Concomitantly, hypothalamo-pituitary-adrenal (HPA) activity as indicated by cortisol release is suppressed to a minimum during early sleep, while drastically increasing during late sleep. We have shown that the different sleep stages and the concomitant glucocorticoid release are interactively involved in the consolidation of different types of memories. SWS-rich early sleep has been demonstrated to benefit mainly the consolidation of hippocampus-dependent declarative memories (i.e. facts and episodes). In contrast, REM sleep-rich late sleep was shown to improve in particular emotional memories involving amygdalar function, as well as procedural memories (for skills) not depending on hippocampal or amygdalar function. Enhancing plasma glucocorticoid concentrations during SWS-rich early sleep counteracted hippocampus-dependent declarative memory consolidation, but did not affect hippocampus-independent procedural memory. Preventing the increase in cortisol during late REM sleep-rich sleep by administration of metyrapone impaired hippocampus-dependent declarative memory but enhanced amygdala-dependent emotional aspects of memory. The data underscore the importance of pituitary-adrenal inhibition during early SWS-rich sleep for efficient consolidation of declarative memory. The increase in cortisol release during late REM sleep-rich sleep may counteract an overshooting consolidation of emotional memories.     

A daytime nap containing solely non-REM sleep enhances declarative but not procedural memory

The specialized role that sleep-specific brain physiology plays in memory processing is being rapidly clarified with a greater understanding of the dynamic, complex, and exquisitely orchestrated brain state that emerges during sleep. Behaviorally, the facilitative role of non-REM (NREM) sleep (primarily slow wave sleep) for declarative but not procedural memory performance in humans has been demonstrated in a number of nocturnal sleep studies. However, subjects in these studies were tested after periods of sleep that contained REM sleep in addition to NREM sleep, and comparison wake groups were subjected to mild sleep deprivation. To add some clarity to the findings of these nocturnal studies, we assessed performance on declarative and procedural memory tasks following a daytime training-retest interval containing either a short nap that included NREM without REM sleep, or wakefulness. Consistent with previous findings we show that, after a comparatively brief sleep episode, subjects that take a nap improve more on a declarative memory task than subjects that stay awake, but that improvement on a procedural memory task is the same regardless of whether subjects take a nap or remain awake. Slow wave sleep was the only sleep parameter to correlate positively with declarative memory improvement. These findings are discussed with reference to the general benefits of napping and within the broader context of a growing literature suggesting a role for NREM-specific physiology for the processing of declarative memory.     

Spatial and reversal learning in the Morris water maze are largely resistant to six hours of REM sleep deprivation following training

This first test of the role of REM (rapid eye movement) sleep in reversal spatial learning is also the first attempt to replicate a much cited pair of papers reporting that REM sleep deprivation impairs the consolidation of initial spatial learning in the Morris water maze. We hypothesized that REM sleep deprivation following training would impair both hippocampus-dependent spatial learning and learning a new target location within a familiar environment: reversal learning. A 6-d protocol was divided into the initial spatial learning phase (3.5 d) immediately followed by the reversal phase (2.5 d). During the 6 h following four or 12 training trials/day of initial or reversal learning phases, REM sleep was eliminated and non-REM sleep left intact using the multiple inverted flowerpot method. Contrary to our hypotheses, REM sleep deprivation during four or 12 trials/day of initial spatial or reversal learning did not affect training performance. However, some probe trial measures indicated REM sleep-deprivation-associated impairment in initial spatial learning with four trials/day and enhancement of subsequent reversal learning. In naive animals, REM sleep deprivation during normal initial spatial learning was followed by a lack of preference for the subsequent reversal platform location during the probe. Our findings contradict reports that REM sleep is essential for spatial learning in the Morris water maze and newly reveal that short periods of REM sleep deprivation do not impair concurrent reversal learning. Effects on subsequent reversal learning are consistent with the idea that REM sleep serves the consolidation of incompletely learned items.     

Sleep physiology and psychological aspects of the fibrositis (fibromyalgia) syndrome

Fibrositis (fibromyalgia) patients were compared with normal controls in terms of electrophysiology (EEG), self-report indicants of awakening, quality of sleep, behaviourally signalled awakenings, and Symptom Check List 90R (SCL-90R) scores. The results differentiated fibrositis patients from normal controls in terms of SCL-90R scores, with fibrositis patients showing significantly more psychopathology. Fibrositis patients had more alpha EEG sleep and less REM and Stage 1 sleep. They were better able to recall their behaviourally signalled awakenings the following morning and reported qualitatively less satisfying sleep than the normal controls. The alpha EEG sleep anomaly may reflect a vigilant arousal state during nocturnal sleep and result in the daytime experience of unrefreshing sleep, psychologic distress, that re-enforces the perpetuation of the sleep-related symptoms.     

Electroencephalographic and autonomic alterations in subjects with frequent nightmares during pre-and post-REM periods

Abnormal arousal processes, sympathetic influences, as well as wake-like alpha activity during sleep were reported as pathophysiological features of Nightmare Disorder. We hypothesized that in Nightmare Disorder, wake-like cortical activity and peripheral measures linked to arousals would be triggered by physiological processes related to the initiation of REM periods. Therefore, we examined electroencephalographic (EEG), motor and autonomous (cardiac) activity in a group of nightmare (NM) and healthy control (CTL) subjects during sleep-state-transitions while controlling for the confounding effects of trait anxiety. Based on the second-nights’ polysomnographic recordings of 19 Nightmare Disordered (NM) and 21 control (CTL) subjects, we examined the absolute power spectra focusing on the alpha range, measures of heart rate variability (HRV) and motor (muscle tone) activity during pre-REM and post-REM periods, separately. According to our results, the NM group exhibited increased alpha power during pre-REM, but not in post-REM, or stable, non-transitory periods. While CTL subjects showed increased HRV during pre-REM periods in contrast to post-REM ones, NM subjects did not exhibit such sleep state-specific differences in HRV, but showed more stable values across the examined sleep stages and less overall variability reflecting generally attenuated parasympathetic activity during sleep-state-transitions and during stable, non-transitory NREM states. These differences were not mediated by waking levels of trait anxiety. Moreover, in both groups, significant differences emerged regarding cortical and motor (muscle tone) activity between pre-REM and post-REM conditions, reflecting the heterogeneity of NREM sleep. Our findings indicate that NM subjects’ sleep is compromised during NREM–REM transitions, but relatively stabilized after REM periods. The coexistence of sleep-like and wake-like cortical activity in NM subjects seems to be triggered by REM/WAKE promoting neural activity. We propose that increased arousal-related phenomena in NREM–REM transitions might reflect altered emotional processing in NM subjects.     

Delta and spindle components in the integrated EEG during nocturnal sleep for infants with developmental disabilities

The delta and spindle components in the integrated EEG for 121 infants with developmental disabilities (from 4 mo. to 6 yr. of age: M=1.79, SD=0.14; 57 girls and 64 boys) were studied throughout nocturnal sleep. In 80 (66.1%, Group A) of 121 subjects, periodic changes of delta and spindle rhythm powers were noted in measurements of EEG made during sleep. In 28 (23.1%, Group B), delta but not spindle rhythm powers were found, and in the remaining 13 subjects (10.7%, Group C) neither delta nor spindle rhythm powers were found throughout measurements of EEG made during sleep. The Tsumori-Inage Questionnaire for Infants was administered to the parents to estimate subjects' behavioral developmental level as Developmental Quotients. Significantly lower mean Developmental Quotients were found for Groups B and C than Group A. These findings suggested that the presence or absence of delta and spindle rhythm powers in EEG measurements made during nocturnal sleep could be taken as an index of the severity of developmental disorders in infants with developmental disabilities.     

REM sleep: A social bonding mechanism

It is proposed that REm sleep evolved, in part, to promote social bonding between (1) a mammalian infant and the mother and (2) sexual partners. The bonding hypothesis is consistent with the available evidence from psychobiologic studies of the attachment process in infants, with the known physiologic correlates of REM sleep, with the facts concerning the ontogeny and the phylogeny of REM sleep, and with phenomenological properties of dreams.     

Possible contribution of better maternal psychological well-being to the acquisition of sleeping through the night in infants during the early postpartum period

The objective of this study was to elucidate whether better maternal psychological well-being contributes to the acquisition of “sleeping through the night” (STN) in infants during the early postpartum period. Fifty-two primiparous mothers completed the General Health Questionnaire-28 (GHQ-28) in the third trimester (prenatal) and when the conceptional ages of their babies reached 8–9 weeks (hereafter, 2 months), 12–13 weeks (3 months), and 16–17 weeks (4 months). They also recorded babies’ nocturnal sleep patterns in a timetable for 5 consecutive days each month postpartum. “Regular STN” was defined when the mean of longest nocturnal sleep duration for 5 consecutive days was > 8 h or between 6 and 8 h with < 1.0 nocturnal awakenings. According to these criteria, a total of 14 infants (27 %) acquired regular STN at 4 months (referred to as “STN infants”), with STN infants showing a marked increase in longest nocturnal sleep duration and a decrease in nocturnal awakenings from 2 to 3 months of age. The mothers of STN infants demonstrated steady reductions in postnatal GHQ-28 scores and had significantly lower prenatal GHQ-28 scores compared with the mothers of non-STN infants (3.7 ± 3.0 vs. 6.4 ± 4.1, p = 0.027). In random forest models for binomial classification, both prenatal and postnatal (at 4 months) GHQ-28 scores were identified as significant covariates for distinguishing STN infants, and other important covariates, including weeks of delivery, stepfamily, birth weight of the infant, and maternal co-sleeping at bedtime, were selected. Among these covariates, maternal co-sleeping at bedtime had relatively stronger correlations with both STN infants (r = − 0.440) and prenatal maternal GHQ-28 scores (r = 0.377). In conclusion, because prenatal maternal psychological well-being was thought to predict the acquisition of STN in infants, infants born from mothers with better psychological well-being appear to have some advantages in acquiring STN. These cross-lagged correlations suggest that the pathway from mothers to infants may be mediated by certain parenting behaviors, such as maternal co-sleeping at bedtime.     

Rapid eye movement (REM) in premature neonates and developmental outcome at 6 months

Different aspects of early sleep organization have been associated with subsequent development in premature infants. The aim of the present study was to assess the relations between rapid eye movement (REM) activity in premature neonates and infants' developmental outcomes at 6 months. Participants were 81 premature infants (47 males). Sleep-wake states and REM were observed across 4 consecutive evening hours (7-11 PM) in 10-s frames when infants were between 32 and 36 weeks post-menstrual age. Developmental outcome was assessed at 6 months with the mental development index (MDI) of the Bayley II. Infants with low-REM activity spent more time in less growth-promoting states, including crying and unfocused alert states in the neonatal period and had lower MDI scores at 6 months corrected age compared to infants with high-REM. Differences between the high- and low-REM groups were independent of neonatal medical risk. Low-REM activity may serve as an indicator of developmental risk among premature neonates.     

Behavioral treatment of insomnia in older adults: an open clinical trial comparing two interventions

Fifty-five insomniacs, 60 years or above, participated in a behavioral treatment program, comparing two interventions (sleep hygiene+stimulus control vs sleep hygiene+relaxation tape). Half of the subjects were randomized to a waiting-list condition prior to treatment. No significant changes were observed during the waiting-list period. During the treatment period however, the subjects improved on several sleep parameters, and treatment gains were maintained at a 6-month follow-up. The effects of treatment were greater for nocturnal measures (e.g. sleep onset latency and total sleep time) as compared to daytime measures (e.g. life satisfaction, daytime alertness) and not-targeted behavior (medication use). There were no differences in treatment effects for the two interventions.     

Paradoxical sleep and information processing: exploration by inversion of the visual field

The purpose of this study was to test the potential relationship between REM sleep and information processing with inversion of the visual field. In the first experiment, four male subjects slept in the laboratory for two sessions of 6 consecutive nights: 2 adaptation nights, 2 nights of polysomnography, and 2 nights of dream collection. During the days preceding Nights 3, 4, 5, and 6 of each session, the subjects wore glasses which, during the second session, completely inverted (rotation of 180 degrees) their visual field. In a second experiment with four other male subjects, the order of conditions was reversed, and the experimental condition (visual inversion) was introduced a second time. When the data of the two experiments were combined, there was a significant (p less than .01) increase in the percentage of REM sleep from Nights 3 and 4 of the control condition to Nights 3 and 4 of the visual inversion condition, but there was no significant change in any of the other sleep stages. There was a significant decrease in horizontal (p less than .04) and vertical (p less than .005) REM density and in the density of vertical REM bursts (p less than .02). The increase in REM sleep supports the hypothesis that REM sleep contributes to information processing while the decrease in REM density suggests that this component of REM sleep may be involved in a homeostatic process of sensory input.     

Hemispheric lateralization of the EEG during wakefulness and REM sleep in young healthy adults

EEG recordings confirm hemispheric lateralization of brain activity during cognitive tasks. The aim of the present study was to investigate spontaneous EEG lateralization under two conditions, waking and REM sleep. Bilateral monopolar EEG was recorded in eight participants using a 12-electrode montage, before the night (5 min eyes closed) and during REM sleep. Spectral analysis (0.75-19.75 Hz) revealed left prefrontal lateralization on total spectrum amplitude power and right occipital lateralization in Delta activity during waking. In contrast, during REM sleep, right frontal lateralization in Theta and Beta activities and right lateralization in occipital Delta activity was observed. These results suggest that spontaneous EEG activities generated during waking and REM sleep are supported in part by a common thalamo-cortical neural network (right occipital Delta dominance) while additional, possibly neuro-cognitive factors modulate waking left prefrontal dominance and REM sleep right frontal dominance.     

Search activity in the context of psychosomatic disturbances,of brain monoamines and REM sleep function

The author discusses a number of controversial aspects of the search activity concept. This concept, based on an analysis of data cited by other researchers and the results of the author’s own investigation, performed together with V. V. Arshavsky, postulates that search activity raises the body’s resistance to stress and experimentally induced pathology whereas renunciation of search forms a nonspecific predisposition to somatic disturbances (e.g., psychosomatic disease). REM sleep is regarded as a specific form of search activity aimed at compensating for the state of renunciation of search in walking. In this paper the author argues that 1) renunciation of search can be accompanied either by anxiety or by depression, 2) REM sleep deprivation on a “small platform” raises the requirement in REM sleep by producing renunciation of search, 3) during search activity brain catecholamine synthesis is stimulated by catabolism whereas a state of renunciation of search upsets this feedback system. The actuation of the brain mechanisms of search in REM sleep necessitates a certain brain catecholamine level. If the brain catecholamine level is very high during waking behavior due to intensive search activity, the REM sleep requirement is low, REM sleep becoming reduced. After a moderate drop in the brain catecholamine level at the initial stage of renunciation of search the requirement in REM sleep rises and this phase grows longer. But at the late stage of renunciation of search the brain catecholamine level drops extremely, REM sleep shrinking in spite of the great appropriate requirement, and 4) the functional insufficiency of REM sleep invites various forms of pathology.     

Remembering specific features of emotional events across time: The role of REM sleep and prefrontal theta oscillations

When an episode of emotional significance is encountered, it often results in the formation of a highly resistant memory representation that is easily retrieved for many succeeding years. Recent research shows that beyond generic consolidation processes, rapid eye movement (REM) sleep importantly contributes to this effect. However, the boundary conditions of consolidation processes during REM sleep, specifically whether these extend to source memory, have not been examined extensively. The current study tested the effects of putative consolidation processes emerging during REM sleep and slow wave sleep (SWS) on item and source memory of negative and neutral images, respectively. Results demonstrate superior emotional relative to neutral item memory retention after both late night REM sleep and early night SWS. Emotional source memory, on the other hand, exhibited an attenuated decline following late night REM sleep, whereas neutral source memory was selectively preserved across early night SWS. This pattern of results suggests a selective preservation of emotional source memory during REM sleep that is functionally dissociable from SWS-dependent reprocessing of neutral source memory. This was further substantiated by a neurophysiological dissociation: Postsleep emotional source memory was selectively correlated with frontal theta lateralization (REM sleep), whereas postsleep neutral item memory was correlated with SWS spindle power. As such, the present results contribute to a more comprehensive characterization of sleep-related consolidation mechanisms underlying emotional and neutral memory retention. Subsidiary analysis of emotional reactivity to previously encoded material revealed an enhancing rather than attenuating effect of late night REM sleep on emotional responses.     

Interhemispheric EEG coherence during sleep and wakefulness in left- and right-handed subjects

REM sleep is associated with the production of complex imagery sequences. Yet research is divided as to whether different brain regions are more or less coordinated in their functioning at this time. Some research suggests that there may occur a functional disconnection of the left and right cerebral hemispheres during REM sleep which is similar to the disconnection syndrome seen after corpus callosotomy. Other research suggests that an increase in interhemispheric coordination occurs. On the assumption that hemispheric coordination is reflected in the EEG coherence measure, we explored differences in interhemispheric coherence recorded in six left- and six right-handed normal subjects during periods of wakefulness, stage REM, stage 2, and stage 3/4 sleep. Strong evidence was found that mean EEG coherence values are larger during sleep than during waking and that they are approximately equal for the different stages of sleep. Frontal electrode placements demonstrated a slightly different pattern of coherence than central, parietal, or occipital placements. Furthermore, coherence values were larger for left-handed subjects over the occipital region during wakefulness, stage 2, and stage REM sleep, but not during stage 3/4 sleep. Coherence was not different for male and female subjects. These findings oppose the interpretation that a functional disconnection of hemispheres occurs during REM sleep and favor the interpretation that sleep in general is a state of heightened cortical coordination. Moreover, greater interhemispheric coherence over occipital brain regions in left-handed subjects suggests possible differences in the cognitive processes of these subjects during waking and dreaming states.     

REM periodicity under ultrashort sleep/wake cycle in narcoleptic patients

Six narcoleptic patients were tested three times on the 13-min waking/7-min resisting sleep paradigm each time after a night of sleep in the laboratory. The three experiments were conducted after 10 days without any antinarcoleptic treatment or after 2 weeks of daily treatment with either methyl-phenidate or aniracetam. The results showed that patients had pronounced levels of diurnal sleepiness in all three experimental conditions with a midafternoon peak at around 1300-1500 hr and a nadir at around 1800 hr. Methyl-phenidate significantly reduced REM sleep and marginally reduced total sleep in comparison with the no-treatment and aniracetam conditions. REM sleep in the 7/13 paradigm appeared cyclically with a dominant periodicity of 80 min/cycle. The cycles tended to be synchronized across patients and were unrelated to the temporal structure of total sleep. The present results support the continuation of the REM oscillator during brief periods of waking, but suggest that the REM periodicity is unrelated to Kleitman's BRAC model of arousal.     

Cognitive and emotional processes during dreaming: a neuroimaging view

Dream is a state of consciousness characterized by internally-generated sensory, cognitive and emotional experiences occurring during sleep. Dream reports tend to be particularly abundant, with complex, emotional, and perceptually vivid experiences after awakenings from rapid eye movement (REM) sleep. This is why our current knowledge of the cerebral correlates of dreaming, mainly derives from studies of REM sleep. Neuroimaging results show that REM sleep is characterized by a specific pattern of regional brain activity. We demonstrate that this heterogeneous distribution of brain activity during sleep explains many typical features in dreams. Reciprocally, specific dream characteristics suggest the activation of selective brain regions during sleep. Such an integration of neuroimaging data of human sleep, mental imagery, and the content of dreams is critical for current models of dreaming; it also provides neurobiological support for an implication of sleep and dreaming in some important functions such as emotional regulation.