Mental activity after early afternoon nap awakenings in healthy subjects

Despite the common misconception that rapid eye movement (REM) sleep is a unique correlate of dreaming, reports of mental activity can be elicited after awakenings from any stage of nocturnal sleep. We extended the investigation to naps and tried to explore the relationship between recall length and level of sleep stage and depth preceding the awakening. We hypothesized that dream report length would be related to arousal level. In 10 healthy young adults, sleep EEG and EOG were recorded for four non-consecutive early afternoon naps. Dream recalls were recorded following 10 s, 1 min, and 6 min of NREM Stage 2 and after 5 min of first REM period. We measured mental recall with total word count (TWC) method, sleep stages by using EEG visual scoring and Delta and Beta activity by period amplitude (PAA) and power spectral (PSA) analyses. All awakening conditions were followed by a dream report. TWC was significantly greater after REM than after 10 s and 1 min of NREM, and TWC did not differ among the NREM awakenings. Delta activity after REM was significantly lower compared to the NREM 6 and 1 min while Beta activity did not differ across the conditions. Assuming that arousal level decreased with increased NREM duration and increasing Delta EEG activity, the constant TWC across the three NREM awakenings indicates that arousal level cannot be the only factor affecting dream report length. Some other factor such as memory processing may explain the longer dream reports following REM sleep, or it may be that the EEG is an imperfect indicator of arousal level.     

Dream experience during REM and NREM sleep of patients with complex partial seizures

This study examined the effectiveness of the cognitive processes underlying dreaming in patients with complex partial seizures (CPS), by assessing the frequency of recall and the structural organization of dreams reported after awakenings provoked alternately during REM and stage 2 NREM sleep on 12 cognitively unimpaired CPS-patients (six with epileptic focus in the right hemisphere and six in the left one). Each patient was recorded for three consecutive nights, respectively, for adaptation to the sleep laboratory context, for polysomnography and for dream collection. The frequency of dream recall was lower after stage 2 NREM sleep than REM sleep, regardless of the side of epileptic focus, while the length and structural organization of dreams did not significantly differ in REM and NREM sleep. However, the length of story-like dreams was influenced by global cognitive functioning during REM sleep. These findings indicate that in CPSs-patients the elaboration of dream experience is maintained in both REM and NREM sleep, while the access to information for conversion into dream contents and the consolidation of dream contents is much less effective during NREM rather than during REM sleep. Further studies may distinguish between these two possibilities and enlighten us as to whether the impaired memory functioning during NREM sleep is a side effect of anticonvulsant treatment.     

Non-dreamers

OBJECTIVE: Assess incidence and clarify whether diagnostic correlates exist for sleep laboratory patients reporting a lack of dream recall. To awaken, during polysomnographically defined sleep including rapid eye movement (REM) sleep, individuals reporting never having experienced a dream, and determine whether they report dreaming. METHODS: Study # 1 - Incidence and polysomnographic correlates of sleep lab patients responding on questionnaire that they had never experienced dreaming. Study # 2 - Phone interviews with those individuals reporting non-dreaming on questionnaire to reassess incidence. Study # 3 - After reassessment, individuals (non-dreamers - # 16) are awakened during polysomnographic defined sleep (including REM sleep) and queried about dream recall. This group is compared statistically to a group (rare-dreamers - # 12) that reported dreaming as an extremely rare occurrence (mean dream recall latency - 13.5 years). RESULTS: Study # 1: Incidence of questionnaire reported non-dreaming in this sleep laboratory population is 6.5% (N=534) and is associated with the diagnosis of obstructive sleep apnea (specificity 95.6% for respiratory disturbance index >15). Study # 2 - Individuals who report after interview to have never experienced dreaming are more unusual (0.38% of this sleep laboratory population). Study # 3 - None of the non-dreamers (# 16) reported dream recall after waking in the sleep laboratory (36 awakenings in total for this group). This group does not differ, based on polysomnographic, clinical, or demographic variables, from the rare-dreaming group that occasionally reported dreams when awakened (3/12 patients, 3/32 awakenings) - a finding consistent with the reports of previous studies. CONCLUSION: The experience of dreaming may not be as ubiquitous as generally accepted. The group of non-dreamers evaluated in this study reports never having recalled a dream and reports no dreams when awakened during polysomnographicly defined sleep. These individuals might not experience dreaming.     

Sleep-induced changes in associative memory

The notion that dreaming might alter the strength of associative links in memory was first proposed almost 200 years ago. But no strong evidence of such altered associative links has been obtained. Semantic priming can be used to quantify the strength of associative links between pairs of words; it is thought to measure the automatic spread of activation from a "node" representing one word to nodes representing semantically related words. Semantic priming could thus be used to test for global alterations in the strengths of associative links across the wake-sleep cycle. Awakenings from REM and nonREM (NREM) sleep produce a period of state carry-over during which performance is altered as a result of the brain's slow transition to full wakefulness, and cognitive testing in this period can provide information about the functioning of the brain during the prior sleep period. When subjects were tested across the night--before and after a night's sleep as well as immediately following forced awakenings from REM and NREM sleep--weak priming (e. g., thief-wrong) was found to be state dependent (p = 0.016), whereas strong priming (e.g., hot-cold) was not (p = 0.89). Weak primes were most effective in the presleep and REM sleep conditions and least effective in NREM and postsleep conditions. Most striking are analyses comparing weak and strong priming within each wake-sleep state. Contrary to the normal pattern of priming, subjects awakened from REM sleep showed greater priming by weak primes than by strong primes (p = 0.01). This result was seen in each of three protocols. In contrast, strong priming exceeded weak priming in NREM sleep. The shift in weak priming seen after REM sleep awakenings suggests that cognition during REM sleep is qualitatively different from that of waking and NREM sleep and may reflect a shift in associative memory systems, a shift that we hypothesize underlies the bizarre and hyperassociative character of REM-sleep dreaming. Known changes in brainstem activity that control the transition into and maintenance of REM sleep provide a possible explanation of this shift.     

Functions of sleep architecture and the concept of protective fields

This article focuses on the function of human sleep architecture and, where it adjoins, on the ultradian rhythm of NREM and REM cycles. In healthy adult human sleep, NREM and REM sleep succeed each other in 90-110 min intervals. This ultradian pattern of NREM/REM succession is cyclical. Sleep architecture relates to the shifting between sleep stages of varying sleep intensity and arousal thresholds. It has been found to follow a typical but non-cyclical pattern throughout the night. In the first third of the night, light sleep alternates predominantly with slow wave sleep (SWS). As sleep progresses, the amount of SWS typically decreases and REM sleep increases. In the last third of the night, light sleep almost exclusively alternates with REM sleep. The author postulates that one function of the non-cyclical succession of sleep stages is the erection and maintenance of a protective field around the sleeper. A protective field is to be understood as an area of relative safety, minimizing the chances for an intruder to enter the field without detection. The frequent shifts between sleep phases with low and high arousal thresholds allow a periodic screening of the sleep environment for danger signals. The relevant literature on sleep architecture, ultradian rhythms and its determinants is reviewed and the implications of the concept of protective fields are discussed.     

Rapid eye movement sleep,non-rapid eye movement sleep,dreams, and hallucinations

After the discovery of rapid eye movement (REM) sleep in 1953, oneiric activity was long thought to be associated uniquely with REM sleep. Subsequent evaluation of sleep in humans combining neurophysiologic, psychophysiologic, and, more recently, functional neuroimaging investigations, has instead shown that dreaming also occurs during non-REM (NREM) sleep. It has been documented that hallucinatory activity during sleep is a normal phenomenon that is not constant throughout the night but increases toward morning when it tends to become present to the same extent in REM and NREM sleep. The role of sleep mechanisms in the generation of visual hallucinations is well-recognized in narcolepsy in the case of hypnagogic hallucinations, which are thought to derive from a REM-dissociation state in which dream imagery intrudes into wakefulness. Similar mechanisms have been hypothesized to play a role in the physiopathogenesis of visual hallucinations in various neuropsychiatric disorders. Furthermore, a growing body of evidence indicates that not only REM but also NREM processes, such as arousal-related processes, may play a role in the physiopathogenesis of hallucinations in the aforementioned disorders. The role of these processes has been most extensively documented in visual hallucinations occurring in the context of delirium tremens and Parkinson’s disease.     

Cognitive flexibility across the sleep-wake cycle: REM-sleep enhancement of anagram problem solving

Flexible or 'fluid' cognitive processes are regarded as fundamental to problem solving and creative ability, requiring a specific neurophysiological milieu. REM-sleep dreaming is associated with creative processes and abstract reasoning with increased strength of weak associations in cognitive networks. REM sleep is also mediated by a distinctive neurophysiological profile, different to that of wake and NREM sleep. This study compared the performance of 16 subjects on a test of cognitive flexibility using anagram word puzzles following REM and NREM awakenings across the night, and waking performances during the day. REM awakenings provided a significant 32% advantage in the number of anagrams solved compared with NREM awakenings and was equal to that of wake time trials. Correlations of individual performance profiles suggest that REM sleep may offer a different mode of problem solving compared with wake and NREM. When early and late REM and NREM awakening data were separated, a dissociation was evident, with NREM task performance becoming more REM-like later in the night, while REM performance remained constant. These data suggest that the neurophysiology of REM sleep represents a brain state more amenable to flexible cognitive processing than NREM and different from that in wake, and may offer insights into the neurocognitive properties of REM-sleep dreaming.     

Dream process in asthmatic subjects with nocturnal attacks

Polygraphic sleep recordings were made and dream reports collected over 3 consecutive nights for 12 asthmatic subjects with nocturnal attacks and 12 matched normal control subjects. The asthmatic group 1) had more episodes of a vivid impression of dreaming without recollection of dream content ("white dreams") after awakening spontaneously in the morning (nights 1 and 2) and after awakening immediately following REM sleep (night 3), 2) used shorter sentences in dream narrations, and 3) had no dream recall when awakened during nocturnal asthma attacks. The authors suggest that conflictual material emerging during REM or other sleep stages may contribute to the occurrence of nocturnal attacks but is repressed on awakening.     

Parasomnias: An Updated Review

Parasomnias are abnormal behaviors emanating from or associated with sleep. Sleepwalking and related disorders result from an incomplete dissociation of wakefulness from nonrapid eye movement (NREM) sleep. Conditions that provoke repeated cortical arousals, or promote sleep inertia lead to NREM parasomnias by impairing normal arousal mechanisms. Changes in the cyclic alternating pattern, a biomarker of arousal instability in NREM sleep, are noted in sleepwalking disorders. Sleep-related eating disorder (SRED) is characterized by a disruption of the nocturnal fast with episodes of feeding after an arousal from sleep. SRED is often associated with the use of sedative-hypnotic medications; in particular, the widely prescribed benzodiazepine receptor agonists. Recently, compelling evidence suggests that nocturnal eating may in some cases be a nonmotor manifestation of Restless Legs Syndrome (RLS). rapid eye movement (REM) Sleep Behavior Disorder (RBD) is characterized by a loss of REM paralysis leading to potentially injurious dream enactment. The loss of atonia in RBD often predates the development of Parkinson??s disease and other disorders of synuclein pathology. Parasomnia behaviors are related to an activation (in NREM parasomnias) or a disinhibition (in RBD) of central pattern generators (CPGs). Initial management should focus on decreasing the potential for sleep-related injury followed by treating comorbid sleep disorders. Clonazepam and melatonin appear to be effective therapies in RBD, whereas paroxetine has been reported effective in some cases of sleep terrors. At this point, pharmacotherapy for other parasomnias is less certain, and further investigations are necessary.     

Dream Content Analysis in Persons with an Autism Spectrum Disorder

Dream questionnaires were completed by 28 young adults with autism spectrum disorder (ASD) participants. Seventy-nine typically developed individual served as the control group. In a subset of 17 persons with ASD and 11 controls matched for verbal IQ, dream narratives were obtained following REM sleep awakenings in a sleep laboratory. Questionnaires revealed that participants with ASD, compared to controls, had fewer recollections of dreaming, fewer bad dreams and fewer emotions. In the sleep laboratory, dream content narratives following REM sleep awakenings were shorter in ASD participants than in controls. ASD participants also reported fewer settings, objects, characters, social interactions, activities, and emotions. It is concluded that these characteristics of dreaming in ASD may reflect neurocognitive dimensions specific to this condition.     

Sleep paralysis in narcolepsy: more than just a motor dissociative phenomenon?

Sleep paralyses are viewed as pure motor phenomena featured by a dissociated state in which REM-related muscle atonia coexists with a wakefulness state of full consciousness. We present a 59-year-old man diagnosed with narcolepsy experiencing sleep paralysis, who failed to establish the boundaries between real experience and dream mentation during the paralysis: the patient’s recall was indeed featured by uncertainty between real/unreal and awaken/dreaming. Hereby, we suggest that sleep paralysis may represent a more complex condition encompassing a dissociated state of mind together with the dissociative motor component. Neurophysiological data (spectral EEG analysis corroborated by cross-correlation analysis) reinforce the idea that the patient was in an intermediate state of mind between wake and REM sleep during the paralysis. The persistence of local impaired activity proper of REM sleep in cortical circuits necessary for self-reflective awareness and insight, in conflict with wakefulness-related activation of the remaining brain areas, could account for disrupted processing of afferent inputs in our patient, representing the underlying pathophysiologic substrate for patient’s failure to establish the boundaries between real experience and dream mentation.     

Do all mammals dream?

The presence of dreams in human sleep, especially in REM sleep, and the detection of physiologically similar states in mammals has led many to ponder whether animals experience similar sleep mentation. Recent advances in our understanding of the anatomical and physiological correlates of sleep stages, and thus dreaming, allow a better understanding of the possibility of dream mentation in nonhuman mammals. Here, we explore the potential for dream mentation, in both non-REM and REM sleep across mammals. If we take a hard-stance, that dream mentation only occurs during REM sleep, we conclude that it is unlikely that monotremes, cetaceans, and otariid seals while at sea, have the potential to experience dream mentation. Atypical REM sleep in other species, such as African elephants and Arabian oryx, may alter their potential to experience REM dream mentation. Alternatively, evidence that dream mentation occurs during both non-REM and REM sleep, indicates that all mammals have the potential to experience dream mentation. This non-REM dream mentation may be different in the species where non-REM is atypical, such as during unihemispheric sleep in aquatic mammals (cetaceans, sirens, and Otariid seals). In both scenarios, the cetaceans are the least likely mammalian group to experience vivid dream mentation due to the morphophysiological independence of their cerebral hemispheres. The application of techniques revealing dream mentation in humans to other mammals, specifically those that exhibit unusual sleep states, may lead to advances in our understanding of the neural underpinnings of dreams and conscious experiences.     

Investigations of morning and laboratory dream recall and content in depressive patients during baseline conditions and under antidepressive treatment with trimipramine

REM sleep abnormalities like shortened REM (rapid eye movement) latency, prolongation of the first REM period and heightening of REM density often found in patients with a major depression have prompted an increasing number of studies investigating the neurobiology and neurophysiology of REM sleep in depressive patients, as well as in healthy humans and animals. On the other hand, since the early 1970s investigation of the psychological concomitant of REM sleep, i.e., dreaming, in depressive patients has been extremely sparse. The present study aimed at investigating morning and laboratory dream recall and content in patients with a major depressive disorder to shed more light on this neglected area. In short, morning as well as laboratory dream recall in depressive inpatients was drastically reduced. The low number of scorable dream reports collected did not reveal a heightened incidence of "masochistic" or "negative" content, indeed were rather mundane. In contrast, depressive outpatients (probably less depressed) had a higher rate of morning dream recall. Interestingly, antidepressive treatment with trimipramine (an antidepressant which does not suppress REM sleep) led to a positive influence on patients' mood that was paralleled by a change of dream mood in a positive direction.     

Rapid eye movement sleep patterns of brain activation and deactivation occur within unique functional networks

Rapid eye movement (REM) sleep is a paradoxical state where the individual appears asleep while the electroencephalogram pattern resembles that of wakefulness. Regional differences in brain metabolism have been observed during REM sleep compared to wakefulness, but it is not known whether the spatial distribution of metabolic differences corresponds to known functional networks in the brain. Here, we use a combination of techniques to evaluate the networks associated with sites of REM sleep activation and deactivation from previously published positron emission tomography studies. We use seed‐based functional connectivity from healthy adults acquired during quiet rest to show that REM‐activation regions are functionally connected in a network that includes retrosplenial cingulate cortex, parahippocampal gyrus, and extrastriate visual cortices, corresponding to components of the default mode network and visual networks. Regions deactivated during REM sleep localize to right‐lateralized fronto‐parietal and salience networks. A negatively correlated relationship was observed between REM‐activation and deactivation networks. Together, these findings show that regional activation and deactivation patterns of REM sleep tend to occur in distinct functional connectivity networks that are present during wakefulness, providing insights regarding the differential contributions of brain regions to the distinct subjective experiences that occur during REM sleep (dreaming) relative to wakefulness.     

Appearance of frontal mid-line theta rhythm during sleep and its relation to mental activity

Fm theta occurred not only during mental tests in the waking state but also during nocturnal sleep in which it was most frequent during REM and secondarily most frequent during stage 1 of NREM sleep. As for the inner experience of the subjects, they frequently reported dream and distinct mentations on awakening from REM sleep whether or not it was accompanied by Fm theta. They reported dream and distinct mentations more frequently when awakened from stage 1 of NREM sleep with Fm theta than when awakened from stage 1 of NREM sleep without Fm theta. Relationship of Fm theta to mental activity during sleep was briefly discussed.     

Activation of visual cortex in REM sleep measured by 24-channel NIRS imaging.

To visualize dreaming brain functions we studied hemodynamic changes in the visual cortex during the transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep, using a 24-channel Near-Infrared Spectroscopy (NIRS) imaging method. Results were compared to the activation in visual cortex by visual stimulation during wakefulness. Subjects were four healthy males between 25 and 49 years of age. Five all-night polysomnographic and NIRS recordings were made. Increases in the oxygenated hemoglobin concentration in visual cortex were observed from nine of 14 REM periods. The activated areas were broader during REM sleep than during visual stimulation. These findings suggest that activation of visual cortex in REM sleep might represent dream-related brain activity.     

Mental activity during sleep

Since remote antiquity humankind has believed in the supernatural origin of dreaming. The scientific approach to mental activity during sleep dates back to the eighteenth century. One hundred years ago, psychoanalysis introduced dream analysis for diagnostic and therapeutic purposes. Only 50 years ago psychophysiology made it possible to collect mental sleep activity by means of experimental awakenings while monitoring physiological variables; this approach encouraged investigation into the relationship between the features of sleep activity and sleep state (REM versus NREM). Advances in neurophysiology, in neurochemistry, and recently in brain imaging techniques, have shed light on the roles played by the different cerebral structures in determining specific characteristics of mental activity during sleep. The development of cognitive psychology has enabled investigation of dream generation in terms of output from a complex multilevel system of information processing. In addition to sleep state, other factors, such as the time of the night and the sequence of the NREM-REM cycles, have been shown to influence the characteristics of mental activity. The usefulness of investigation of mental sleep activity as a clinical tool is controversial. The psychophysiological approach to mental sleep activity in clinical contexts has enabled the exploration of adaptation processes and contributed to neuropsychological studies on focal and systemic brain pathology.     

Michel Jouvet: an explorer of dreams and a great storyteller

In the late 50s Michel Jouvet discovered the presence of muscle atonia during REM sleep in cats and created the first model of REM sleep behavior disorder. He built and led in Lyon, France, the “Laboratory of Molecular Dream Science” (a merry oxymoron to silently protest against the research policy of favoring molecular biology over physiology), where in the late 80s, you could cross people who had worked on sleep in the python, tench fish, tortoise, iguana, hen, lamb, mouse, rat and cat. This brilliant physiologist was also a great storyteller with a very good sense of humor. He supported the theory that dreaming is equivalent to REM sleep (which he called “paradoxical sleep”), kept his own dream diary, and imagined that the ponto-geniculo-occipital waves during REM sleep could compose the song sheet of dreams. He wrote several books published in French on dreams and dreaming.     

Perception of dreams and subjective sleep quality in patients with myasthenia gravis

OBJECTIVES: Recent reports have led to the hypothesis of a central nervous system involvement in myasthenia gravis (MG). As the central cholinergic system also plays an important role in sleep/wake rhythms and in the regulation of REM sleep, sleep perception and dreaming may be altered in MG patients. PATIENTS AND METHODS: Seventeen consecutive patients with MG (mean age 49.5 +/- 13.6 years) and 14 healthy controls (mean age 50.5 +/- 16.0 years) were investigated by means of the Self-Rating Depression Scale, Self-Rating Anxiety Scale, Quality of Life Index, Pittsburgh Sleep Quality Index, and Epworth Sleepiness Scale as well as a self-rating questionnaire for sleep and awakening quality and dreaming for 2 weeks. RESULTS: Subjective sleep and awakening quality and sleep efficiency were reduced (p < 0.05), and the number of nocturnal awakenings (p = 0.02) as well as dream recall frequency (p = 0.02) were increased in patients with MG. Patients reported more often body-related and tactile sensations during dreaming (p = 0.001) and dreamed less often visually (p = 0.04). Dream content, emotions, and dream sources did not differ between both groups. Whereas the number of awakenings was related to dream recall frequency in healthy controls, no such a relationship was found in the patient group. CONCLUSION: There is no clear evidence for the arousal-retrieval model of dream recall in patients with MG, but more for the continuity hypothesis of dreaming. Other factors such as the functional state of the brain, possibly related to a central cholinergic involvement in MG or its anticholinesterase treatment, may be important in explaining dream recall in this patient group.     

EEG activities during elicited sleep onset REM and NREM periods reflect different mechanisms of dream generation. Electroencephalograms. Rapid eye movement.

OBJECTIVE: To be the first to compare EEG power spectra during sleep onset REM periods (SOREMP) and sleep onset NREM periods (NREMP) in normal individuals and relate this to dream appearance processes underlying these different types of sleep periods. METHODS: Eight healthy undergraduates spent 7 consecutive nights in the sleep lab including 4 nights for SOREMP elicitation using the Sleep Interruption Technique. This enabled us to control preceding sleep processes between SOREMP and NREMP. EEG power spectra when participants did and did not report 'dreams' were compared between both types of sleep. Sleep stages, subjective measurements including dream property scores, sleepiness, mood, and tiredness after awakenings were also examined to determine their consistency with EEG findings. RESULTS: Increased alpha EEG activities (11.72-13.67 Hz) observed mainly in the central area were related to the absence of SOREMP dreams and appearance of NREMP dreams. Analyses of sleep stages combining two studies (16 participants) also supported the Fast Fourier Transform findings, showing that when dreams were reported there were decreased amounts of stage 2 and increased stage REM in SOREMP and increased stage W in NREMP. SOREMP dreams were more bizarre than NREMP dreams. Participants felt more tired after SOREMP with dreams than without dreams, while the opposite was observed after NREMP episodes. CONCLUSIONS: EEG power spectra patterns reflected different physiological mechanisms underlying generation of SOREMP and NREMP dreams. The same relationships were also reflected by sleep stage analyses as well as subjective measurements including dream properties and tiredness obtained after awakenings. This study not only supports the hypothesized relationships between REM mechanisms and REM dreams as well as arousal processes and NREM dreams, it also provides a new perspective to dream research due to its unique techniques to awaken participants and collect REM dreams during experimentally induced SOREMP.