Dreaming and REM sleep are controlled by different brain mechanisms

The paradigmatic assumption that REM sleep is the physiological equivalent of dreaming is in need of fundamental revision. A mounting body of evidence suggests that dreaming and REM sleep are dissociable states, and that dreaming is controlled by forebrain mechanisms. Recent neuropsychological, radiological, and pharmacological findings suggest that the cholinergic brain stem mechanisms that control the REM state can only generate the psychological phenomena of dreaming through the mediation of a second, probably dopaminergic, forebrain mechanism. The latter mechanism (and thus dreaming itself) can also be activated by a variety of nonREM triggers. Dreaming can be manipulated by dopamine agonists and antagonists with no concomitant change in REM frequency, duration, and density. Dreaming can also be induced by focal forebrain stimulation and by complex partial (forebrain) seizures during nonREM sleep, when the involvement of brainstem REM mechanisms is precluded. Likewise, dreaming is obliterated by focal lesions along a specific (probably dopaminergic) forebrain pathway, and these lesions do not have any appreciable effects on REM frequency, duration, and density. These findings suggest that the forebrain mechanism in question is the final common path to dreaming and that the brainstem oscillator that controls the REM state is just one of the many arousal triggers that can activate this forebrain mechanism. The "REM-on" mechanism (like its various NREM equivalents) therefore stands outside the dream process itself, which is mediated by an independent, forebrain "dream-on" mechanism.     

Dreaming and the brain: toward a cognitive neuroscience of conscious states

Sleep researchers in different disciplines disagree about how fully dreaming can be explained in terms of brain physiology. Debate has focused on whether REM sleep dreaming is qualitatively different from nonREM (NREM) sleep and waking. A review of psychophysiological studies shows clear quantitative differences between REM and NREM mentation and between REM and waking mentation. Recent neuroimaging and neurophysiological studies also differentiate REM, NREM, and waking in features with phenomenological implications. Both evidence and theory suggest that there are isomorphisms between the phenomenology and the physiology of dreams. We present a three-dimensional model with specific examples from normally and abnormally changing conscious states.     

Testing the involvement of the prefrontal cortex in lucid dreaming: A tDCS study

Recent studies suggest that lucid dreaming (awareness of dreaming while dreaming) might be associated with increased brain activity over frontal regions during rapid eye movement (REM) sleep. By applying transcranial direct current stimulation (tDCS), we aimed to manipulate the activation of the dorsolateral prefrontal cortex (DLPFC) during REM sleep to increase dream lucidity. Nineteen participants spent three consecutive nights in a sleep laboratory. On the second and third nights they randomly received either 1 mA tDCS for 10 min or sham stimulation during each REM period starting with the second one. According to the participants’ self-ratings, tDCS over the DLPFC during REM sleep increased lucidity in dreams. The effects, however, were not strong and found only in frequent lucid dreamers. While this indicates some preliminary support for the involvement of the DLPFC in lucid dreaming, further research, controlling for indirect effects of stimulation and including other brain regions, is needed.     

Dreaming,cognition, and physical illness: Part I

Part I of a two part article on the effect upon dreaming on physical illness briefly explores the historical medico-philosophical antecedents of the notion that dreams can be diagnostic of bodily disease. Modern sleep research findings relating REM sleep to physiologic changes are also explored. The controversy of whether dreams are merely the consequence of random brain activity or whether they are a valid psychological phenomenon is discussed. Six contemporary views of the function of REM sleep are outlined. A seventh view of dreaming, that of a “cognitive monitoring system” is suggested. Like earlier historical notions, it is suggested that dreaming is a cognitive activity that processes bodily cues indicating illness or disease. Part II. presents a clinical compendium of dreams relating to Part I.     

The prefrontal cortex in sleep

Experimental data indicate a role for the prefrontal cortex in mediating normal sleep physiology, dreaming and sleep-deprivation phenomena. During nonrandom-eye-movement (NREM) sleep, frontal cortical activity is characterized by the highest voltage and the slowest brain waves compared to other cortical regions. The differences between the self-awareness experienced in waking and its diminution in dreaming can be explained by deactivation of the dorsolateral prefrontal cortex during REM sleep. Here, we propose that this deactivation results from a direct inhibition of the dorsolateral prefrontal cortical neurons by acetylcholine, the release of which is enhanced during REM sleep. Sleep deprivation influences frontal executive functions in particular, which further emphasizes the sensitivity of the prefrontal cortex to sleep.     

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.     

Dreaming and the default network: A review,synthesis, and counterintuitive research proposal

This article argues that the default network, augmented by secondary visual and sensorimotor cortices, is the likely neural correlate of dreaming. This hypothesis is based on a synthesis of work on dream content, the findings on the contents and neural correlates of mind-wandering, and the results from EEG and neuroimaging studies of REM sleep. Relying on studies in the 1970s that serendipitously discovered episodes of dreaming during waking mind-wandering, this article presents the seemingly counterintuitive hypothesis that the neural correlates for dreaming could be further specified in the process of carrying out EEG/fMRI studies of mind-wandering and default network activity. This hypothesis could be tested by asking participants for experiential reports during moments of differentially high levels of default network activation, as indicated by mixed EEG/fMRI criteria. Evidence from earlier EEG/fMRI studies of mind-wandering and from laboratory studies of dreaming during the sleep-onset process is used to support the argument.     

The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming

Several theories claim that dreaming is a random by-product of REM sleep physiology and that it does not serve any natural function. Phenomenal dream content, however, is not as disorganized as such views imply. The form and content of dreams is not random but organized and selective: during dreaming, the brain constructs a complex model of the world in which certain types of elements, when compared to waking life, are underrepresented whereas others are over represented. Furthermore, dream content is consistently and powerfully modulated by certain types of waking experiences. On the basis of this evidence, I put forward the hypothesis that the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance. To evaluate this hypothesis, we need to consider the original evolutionary context of dreaming and the possible traces it has left in the dream content of the present human population. In the ancestral environment human life was short and full of threats. Any behavioral advantage in dealing with highly dangerous events would have increased the probability of reproductive success. A dream-production mechanism that tends to select threatening waking events and simulate them over and over again in various combinations would have been valuable for the development and maintenance of threat-avoidance skills. Empirical evidence from normative dream content, children's dreams, recurrent dreams, nightmares, post traumatic dreams, and the dreams of hunter-gatherers indicates that our dream-production mechanisms are in fact specialized in the simulation of threatening events, and thus provides support to the threat simulation hypothesis of the function of dreaming.     

REM mentation in narcoleptics and normals: an empirical test of two neurocognitive theories

This study tested the two main neurocognitive models of dreaming by using cognitive data elicited from REM sleep in normals and narcoleptics. The two models were the "activation-only" view which holds that, in the context of sleep, overall activation of the brain is sufficient for consciousness to proceed in the manner of dreaming (e.g., Antrobus, 1991; Foulkes, 1993; Vogel, 1978); and the Activation, Input source, Modulation (AIM model), which predicts that not only brain activation level but also neurochemical modulatory systems exert widespread effects upon dreaming (Hobson & McCarley, 1977; Hobson, Pace-Schott, & Stickgold, 2000). Mental activity was studied in nocturnal REM in 15 narcoleptics and 9 normal healthy persons and in REM at the onset of daytime naps and nighttime sleep (SOREM) in narcoleptics. The study was performed in the subjects' homes, using instrumental awakenings and ambulatory polysomnographic techniques, and focused upon visual vividness, mentation report length, improbable and discontinuous bizarre features, and reflective consciousness. Within each subject group, most cognitive variables tended to fluctuate in line with expected variations in circadian activation level. When comparing the cognitive variables between the two groups, reflective consciousness was clearly highest in narcoleptics, whereas improbabilities and discontinuities were lower, with mentation report length and visual vividness differing less between the groups. These findings are consistent with the AIM model of sleep mentation, but not with the activation-only model.     

William James''s The Fringe of Consciousness REM Mentation in Narcoleptics and Normals: Reply to Tore Nielsen

This study tested the two main neurocognitive models of dreaming by using cognitive data elicited from REM sleep in normals and narcoleptics. The two models were the "activation-only" view which holds that, in the context of sleep, overall activation of the brain is sufficient for consciousness to proceed in the manner of dreaming (e.g., Antrobus, 1991; Foulkes, 1993; Vogel, 1978); and the Activation, Input source, Modulation (AIM model), which predicts that not only brain activation level but also neurochemical modulatory systems exert widespread effects upon dreaming (Hobson & McCarley, 1977; Hobson, Pace-Schott, & Stickgold, 2000). Mental activity was studied in nocturnal REM in 15 narcoleptics and 9 normal healthy persons and in REM at the onset of daytime naps and nighttime sleep (SOREM) in narcoleptics. The study was performed in the subjects' homes, using instrumental awakenings and ambulatory polysomnographic techniques, and focused upon visual vividness, mentation report length, improbable and discontinuous bizarre features, and reflective consciousness. Within each subject group, most cognitive variables tended to fluctuate in line with expected variations in circadian activation level. When comparing the cognitive variables between the two groups, reflective consciousness was clearly highest in narcoleptics, whereas improbabilities and discontinuities were lower, with mentation report length and visual vividness differing less between the groups. These findings are consistent with the AIM model of sleep mentation, but not with the activation-only model.     

Dreaming,cognition, and physical illness: Part II

Part II of this two-part article on the effect of dreaming on physical illness presents clinical research and case study data of the relation of REM sleep on physiologic change. Content analysis and the “symbolism” of dreams is explored for their cognitive significance in terms of their diagnostic functions. The medico-ethical implication of the findings are discussed, along with areas of future research.     

Cerebral blood flow in normal and abnormal sleep and dreaming

Measurements of regional or local cerebral blood flow (CBF) by the xenon-133 inhalation method and stable xenon computerized tomography CBF (CTCBF) method were made during relaxed wakefulness and different stages of REM and non-REM sleep in normal age-matched volunteers, narcoleptics, and sleep apneics. In the awake state, CBF values were reduced in both narcoleptics and sleep apneics in the brainstem and cerebellar regions. During sleep onset, whether REM or stage I-II, CBF values were paradoxically increased in narcoleptics but decreased severely in sleep apneics, while in normal volunteers they became diffusely but more moderately decreased. In REM sleep and dreaming CBF values greatly increased, particularly in right temporo-parietal regions in subjects experiencing both visual and auditory dreaming.     

Cognitive asymmetry and dreaming: lack of relationship

The present study investigated the relationship between cognitive laterality and dream recall, dream characteristics, and eye movement density in rapid eye movement (REM) sleep. Fifty-two right-handed males, age 20-30 years, were tested on a six-test battery of which three tests measure right hemisphere function and three tests measure left hemisphere function. Based on their performance, 14 subjects were selected for a sleep laboratory study. Each spent 3 experimental nights in the laboratory during which they were awakened from REM sleep for dream reports. Dream reports were scored for bizarreness, emotions, visual elements, and overall "dreamlike" versus "thoughtlike" character. Subjects were awakened from 123 REM periods, of which 96 yielded positive dream reports (78.04%). Neither the rate of recall nor the four evaluation scores were correlated with the laterality scores that were constructed from the six-test battery. Eye movement density during REM sleep was significantly positively correlated with the total performance of the two hemispheres. These results do not support the alleged lateralization of dreaming. In agreement with recent reports in the literature, it is concluded that dreaming cannot be seen as a "right hemisphere" function.     

Normal body scheme and absent phantom limb experience in amputees while dreaming

While dreaming amputees often experience a normal body image and the phantom limb may not be present. However, dreaming experiences in amputees have mainly been collected by questionnaires. We analysed the dream reports of amputated patients with phantom limb collected after awakening from REM sleep during overnight videopolysomnography (VPSG). Six amputated patients underwent overnight VPSG study. Patients were awakened during REM sleep and asked to report their dreams. Three patients were able to deliver an account of a dream. In all dreaming recalls, patients reported that the amputated limbs were intact and completely functional and they no longer experienced phantom limb sensations. Phantom limb experiences, that during wake result from a conflict between a pre-existing body scheme and the sensory information on the missing limb, were suppressed during sleep in our patients in favour of the image of an intact body accessed during dream.     

Motivation and affect in REM sleep and the mentation reporting process

Although the emotional and motivational characteristics of dreaming have figured prominently in folk and psychoanalytic conceptions of dream production, emotions have rarely been systematically studied, and motivation, never. Because emotions during sleep lack the somatic components of waking emotions, and they change as the sleeper awakens, their properties are difficult to assess. Recent evidence of limbic system activation during REM sleep suggests a basis in brain architecture for the interaction of motivational and cognitive properties in dreaming. Motivational and emotional content in REM and NREM laboratory mentation reports from 25 participants were compared. Motivational and emotional content was significantly greater in REM than NREM sleep, even after controlling for the greater word count of REM reports.     

Continuity between waking activities and dream activities

Empirical studies largely support the continuity hypothesis of dreaming. Despite of previous research efforts, the exact formulation of the continuity hypothesis remains vague. The present paper focuses on two aspects: (1) the differential incorporation rate of different waking-life activities and (2) the magnitude of which interindividual differences in waking-life activities are reflected in corresponding differences in dream content. Using a correlational design, a positive, non-zero correlation coefficient will support the continuity hypothesis. Although many researchers stress the importance of emotional involvement on the incorporation rate of waking-life experiences into dreams, formulated the hypothesis that highly focused cognitive processes such as reading, writing, etc. are rarely found in dreams due to the cholinergic activation of the brain during dreaming. The present findings based on dream diaries and the exact measurement of waking activities replicated two recent questionnaire studies. These findings indicate that it will be necessary to specify the continuity hypothesis more fully and include factors (e.g., type of waking-life experience, emotional involvement) which modulate the incorporation rate of waking-life experiences into dreams. Whether the cholinergic state of the brain during REM sleep or other alterations of brain physiology (e.g., down-regulation of the dorsolateral prefrontal cortex) are the underlying factors of the rare occurrence of highly focused cognitive processes in dreaming remains an open question. Although continuity between waking life and dreaming has been demonstrated, i.e., interindividual differences in the amount of time spent with specific waking-life activities are reflected in dream content, methodological issues (averaging over a two-week period, small number of dreams) have limited the capacity for detecting substantial relationships in all areas. Nevertheless, it might be concluded that the continuity hypothesis in its present general form is not valid and should be elaborated and tested in a more specific way.     

Dreaming and waking: similarities and differences revisited

Dreaming is often characterized as lacking high-order cognitive (HOC) skills. In two studies, we test the alternative hypothesis that the dreaming mind is highly similar to the waking mind. Multiple experience samples were obtained from late-night REM sleep and waking, following a systematic protocol described in Kahan (2001). Results indicated that reported dreaming and waking experiences are surprisingly similar in their cognitive and sensory qualities. Concurrently, ratings of dreaming and waking experiences were markedly different on questions of general reality orientation and logical organization (e.g., the bizarreness or typicality of the events, actions, and locations). Consistent with other recent studies (e.g., [Bulkeley and Kahan, 2008] and [Kozmová and Wolman, 2006] ), experiences sampled from dreaming and waking were more similar with respect to their process features than with respect to their structural features.     

Recurring themes and images in a series of consecutive REM dreams

A consecutive series of REM dreams were collected from one subject over a period of four nights and examined for recurring themes and images. Analysis suggested a nonrandom pattern of dreaming consistent with the proposition that the themes and images are held as elements in a limited capacity storage system from which they can be recycled. One such system can be described by means of a simple testable mathematical model. Some of the implications of this are discussed.     

Dreaming as a 'curtain of illusion': Revisiting the 'royal road' with Bion as our guide

One of Bion's most unique contributions to psychoanalysis is his conception of dreaming in which he elaborates, modifies, and extends Freud 's ideas. While Freud dealt extensively with dream-work, he showed more interest in dreams themselves and their latent meaning and theorized that dreams ultimately constituted wish-fulfillments originating from the activity of the pleasure principle. Bion, on the other hand, focuses more on the process of dreaming itself and believes that dreaming occurs throughout the day as well as the night and serves the reality principle as well as the pleasure principle. In order for wakeful consciousness to occur, dreaming must absorb (contain) the day residue, and transfer it to System Ucs . from System Cs . for it to be processed (transformed) and then returned to System Cs . through the selectively-permeable contact-barrier. Dreaming, consequently, allows the subject to remain awake by day and asleep by night by its processing of the day's residue. Bion seems to conceive of dreaming as an ever-present invisible filter that overlays much of our mental life, including perception, as well as attention itself. He further believes that dreaming is a form of thinking that normally involves the collaborative yet oppositional (not conflictual) activity of the reality and pleasure principles as well as the primary and secondary processes. He also conflates Freud 's primary and secondary processes into a single 'binary–oppositional' structure ( Lévi-Strauss, 1958, 1970 ) that he terms 'alpha-function', which constitutes a virtual model that corresponds to the in-vivo activity of dreaming. He further believes that the analyst dreams as he or she listens and interprets and that the analysand likewise dreams while he or she freely associates.     

Psychology impaired?

This article comments on M.J. Layman and J.R. McNamara's (1997) article about remediation for ethics violations. The author addresses the practice of regarding ethical violation, and its subset, boundary violation, and its subset, sexual misconduct, as synonymous. When professional impairment (disability) is seen as equivalent to sexual misconduct, the resulting generalized confusion impedes much needed progress in critical areas. The profession awaits structured assistance from the American Psychological Association to clarify and provide leadership in policy development.