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.     

Approach/avoidance in dreams

The influential threat simulation theory (TST) asserts that dreaming yields adaptive advantage by providing a virtual environment in which threat-avoidance may be safely rehearsed. We have previously found the incidence of biologically threatening dreams to be around 20%, with successful threat avoidance occurring in approximately one-fifth of such dreams. TST asserts that threat avoidance is over-represented relative to other possible dream contents. To begin assessing this issue, we contrasted the incidence of 'avoidance' dreams with that of their opposite: 'approach' dreams. Because TST states that the threat-avoidance function is only fully activated in ecologically valid (biologically threatening) contexts, we also performed this contrast for populations living in both high- and low-threat environments. We find that 'approach' dreams are significantly more prevalent across both contexts. We suggest these results are more consistent with the view that dreaming is generated by reward-seeking systems than by fear-conditioning systems, although reward-seeking is clearly not the only factor determining the content of dreams.     

How to test the threat-simulation theory

Malcolm-Smith, Solms, Turnbull and Tredoux [Malcolm-Smith, S., Solms, M.,Turnbull, O., & Tredoux, C. (2008). Threat in dreams: An adaptation? Consciousness and Cognition, 17, 1281-1291.] have made an attempt to test the Threat-Simulation Theory (TST), a theory offering an evolutionary psychological explanation for the function of dreaming [Revonsuo, A. (2000a). The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences, 23(6), 877-901]. Malcolm-Smith et al. argue that empirical evidence from their own study as well as from some other studies in the literature does not support the main predictions of the TST: that threatening events are frequent and overrepresented in dreams, that exposure to real threats activates the threat-simulation system, and that dream threats contain realistic rehearsals of threat avoidance responses. Other studies, including our own, have come up with results and conclusions that are in conflict with those of Malcolm-Smith et al. In this commentary, we provide an analysis of the sources of these disagreements, and their implications to the TST. Much of the disagreement seems to stem from differing interpretations of the theory and, consequently, of differing methods to test it.     

Dreams are more negative than real life: Implications for the function of dreaming

Dream content studies have revealed that dream experiences are negatively biased; negative dream contents are more frequent than corresponding positive dream contents. It is unclear, however, whether the bias is real or due to biased sampling, i.e., selective memory for intense negative emotions. The threat simulation theory (TST) claims that the negativity bias is real and reflects the evolved biological function of dreaming. In the present study, we tested the hypothesis of the TST that threatening events are overrepresented in dreams, i.e., more frequent and more severe in dreams than in real life. To control for biased sampling, we used as a baseline the corresponding negative events in real life rather than the corresponding positive events in dreams. We collected dream reports (N=419) and daily event logs (N=490) from 39 university students during a two-week period, and interviewed them about real threat experiences retrievable from autobiographical memory (N=714). Threat experiences proved to be much more frequent and severe in dreams than in real life, and Current Dream Threats more closely resembled Past than Current Real Threats. We conclude that the TST's predictions hold, and that the negativity bias is real.     

Does COVID-19 impact the frequency of threatening events in dreams? An exploration of pandemic dreaming in light of contemporary dream theories

Ninety-one dreams collected during the Covid-19 pandemic (the epidemic-situation sample) were compared with ninety-one dreams collected before the start of the epidemic (the non-epidemic-situation sample). The dreams were classified according to their content, using methods based on previous studies. The frequency of themes was compared to predictions that would be anticipated by three contemporary theories of dreaming: 1) threat simulation theory (TST); 2) incorporation continuity hypothesis (ICH); and 3) social simulation theory (SST). The epidemic-situation sample dreamed more of threatening events than the non-epidemic-situation sample (supporting the TST) and more of non-aggression threatening events, possibly due to the hyperassociation during sleep. However, the epidemic-situation sample did not show a greater prevalence of illness events in dreams (not supporting the ICH). Additionally, there was no significant difference in social neutral and positive events in dreams between the two samples as would have been predicted by the SST.     

Evolutionary function of dreams: A test of the threat simulation theory in recurrent dreams

proposed an intriguing and detailed evolutionary theory of dreams which stipulates that the biological function of dreaming is to simulate threatening events and to rehearse threat avoidance behaviors. The goal of the present study was to test this theory using a sample of 212 recurrent dreams that was scored using a slightly expanded version of the DreamThreat rating scale. Six of the eight hypotheses tested were supported. Among the positive findings, 66% of the recurrent dream reports contained one or more threats, the threats tended to be dangerous and aimed at the dreamer, and when facing a threat, the dreamer tended to take defensive or evasive actions that were possible and reasonable. However, less than 15% of the recurrent dreams depicted realistic and probable situations critical for one's physical survival or reproductive success and the dreamer rarely succeeded in fleeing the threat despite important and appropriate efforts. The findings thus provide mixed support for the threat simulation theory.     

Threat in dreams: an adaptation?

Revonsuo's influential Threat Simulation Theory (TST) predicts that people exposed to survival threats will have more threat dreams, and evince enhanced responses to dream threats, compared to those living in relatively safe conditions. Participants in a high crime area (South Africa: n=208) differed significantly from participants in a low crime area (Wales, UK: n=116) in having greater recent exposure to a life-threatening event (chi([1,N=186])(2)=14.84, p<.00012). Contrary to TST's predictions, the SA participants reported significantly fewer threat dreams (chi([1,N=287])(2)=6.11, p<.0134), and did not differ from the Welsh participants in responses to dream threats (Fisher's Exact test, p=.2478). Overall, the incidence of threat in dreams was extremely low-less than 20% of dreams featured realistic survival threats. Escape from dream threats occurred in less than 2% of dreams. We conclude that this evidence contradicts key aspects of TST.     

Partial memory reinstatement while (lucid) dreaming to change the dream environment

Lucid dreams often coincide with having control over dream events in real-time, although the limitations of dream control are not completely understood. The current study probed the ability of lucid dreamers to reinstate waking scene memories while dreaming. After brief exposure to an experimental scene, participants were asked to reinstate the scene while lucid dreaming (i.e., change dream scenery to match real-world scene). Qualitative analysis revealed that successful dream scene reinstatements were overwhelmingly inaccurate with respect to the original experimental scene. Importantly, reinstatement inaccuracies held even when the dreamer was aware of them during the dream, suggesting a dissociation between memory access while dreaming and dream imagery. The ability to change the environment of a dream speaks to the high amount of lucid dream control, yet the inaccuracies speak to a lack of detailed control. Reinstating context during lucid sleep offers an experimental method to investigate sleep, dreams, and memory.     

Shooting the messenger won’t change the news

Malcolm-Smith, Solms, Turnbull and Tredoux [Malcolm-Smith, S., Solms, M., Turnbull, O., & Tredoux, C. (2008). Threat in dreams: An adaptation? Consciousness and Cognition, 17, 1281–1291.] conducted a rigorous study that sampled two populations differentially exposed to threat in real life, and found that critical predictions from the Threat Simulation Theory of dreams [Revonsuo, A. (2000a). The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences, 23, 877-901.; Revonsuo, A. (2000b). Did ancestral humans dream for their lives? Behavioral and Brain Sciences, 23, 1063–1082.] were not supported. Specifically, we found no evidence of increased realistic threats to physical survival or enhanced threat avoidance in the dreams of those from the exposed population. Revonsuo and Valli’s [Revonsuo, A., & Valli, K. (2008). How to test the threat simulation theory. Consciousness and Cognition, 17, 1292-1296.] commentary on our study argues that the methods we used are so flawed as to render the results meaningless. In this response article, we address the criticisms raised in their commentary.     

Frequency of Nightmares and Gender Significantly Predict Distressing Dreams of German Athletes Before Competitions or Games

Important sports events are highlights and stressful situations in every athlete's career. This stress might alter the dream content of athletes and consequently evoke disturbed dreaming. In this study, the authors asked 840 German athletes from various sports about distressing dreams on the nights before an important competition or game. About 15% of the athletes stated that they experienced at least 1 distressing dream before an important competition or game during the preceding 12 months. An almost equal number of athletes reported at least 1 distressing dream in their sports career. With respect to the base rate, in about 3% of the events a distressing dream occurred. Reported dream content referred mainly to athletic failure. The main risk factor for an athlete experiencing a distressing dream before a competition appears to be the frequency of experienced nightmares in general. Future research should use diary techniques to study the impact of distressing dreams on the next-day athletic performance in a competition or game.     

Frequency of nightmares and gender significantly predict distressing dreams of German athletes before competitions or games

Important sports events are highlights and stressful situations in every athlete's career. This stress might alter the dream content of athletes and consequently evoke disturbed dreaming. In this study, the authors asked 840 German athletes from various sports about distressing dreams on the nights before an important competition or game. About 15% of the athletes stated that they experienced at least 1 distressing dream before an important competition or game during the preceding 12 months. An almost equal number of athletes reported at least 1 distressing dream in their sports career. With respect to the base rate, in about 3% of the events a distressing dream occurred. Reported dream content referred mainly to athletic failure. The main risk factor for an athlete experiencing a distressing dream before a competition appears to be the frequency of experienced nightmares in general. Future research should use diary techniques to study the impact of distressing dreams on the next-day athletic performance in a competition or game.     

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.     

Reflections on the self state dream

Self psychologists contend that patients with narcissistic personality disorders have dreams which cannot be understood in terms of current psychoanalytic dream theory and that these dreams, called self state dreams, have a different origin and structure. The manifest content of these dreams is said to reveal the reactions of healthy sectors of the psyche to disturbing changes in the condition of the self. Self psychologists are said to be able to understand these dreams directly, without the patients' associations, as portrayals of the dreamers' dread of threats to the integrity of the self. The authors raise questions about these contentions. They conclude that the self state dream will remain a dubious concept until a more extensive psychology of dreaming is provided by self psychologists.     

The evolution of Freud's theory about dreaming.

Freud revised his theory of dreams significantly. First, he discovered the role of the id in dreaming. He hypothesized that the function of dreaming is to gratify an infantile sexual wish, in accordance with the pleasure principle, and thereby to preserve sleep. However, he learned later that anxiety generated by recent events plays a greater role in stimulating dream formation than he had thought and that some dreams actually generate anxiety. These clinical observations caused him, in large part, to revise his theories of dreaming, of anxiety, and of the mental apparatus.     

Nighttime in dreams

Based on the continuity hypothesis of dreaming, a study was designed to examine whether time of day within the dream was related to dream emotions. A sample of 1,612 dreams reported by 444 participants was analyzed. As predicted, dream scenarios set at nighttime were associated with less positive and more negative emotions compared to dream scenarios set at other times of the day. In order to pursue this line of research, it would be fruitful to study the dreams of persons with specific nighttime fears.     

The impact of September 11 on dreaming

This study focuses on a set of dreams related to the September 11, 2001 terrorist attacks and their aftermath, using content analysis and cognitive psychology to explore the interweaving of external public catastrophe and internal psychological processes. The study tests several recent claims in contemporary dream research, including the central image theory of Hartmann [Hartmann, E., & Basile, R. (2003). Dream imagery becomes more intense after 9/11/01. Dreaming, 13(2), 61-66; Hartmann, E., & Brezler, T. (2008). A systematic change in dreams after 9/11/01. Sleep, 31(2), 213-218], the media exposure factor postulated by Propper [Propper, R. E., Stickgold, R., Keeley, R., & Christman, S. D. (2007). Is television traumatic? Dreams, stress, and media exposure in the aftermath of September 11, 2001. Psychological Science, 18(4), 334-340], the continuity hypothesis of Domhoff [Domhoff, W. G. (1996). Finding meaning in dreams: A quantitative approach. New York: Plenum], the cognitive and metacognitive approach of Kahan [Kahan, T. L. (2001). Consciousness in dreaming: A metacognitive approach. In K. Bulkeley (Ed.), Dreams: A reader on the religious, cultural, and psychological dimensions of dreaming (pp. 333-360). New York: Palgrave], and the threat simulation theory of Revonsuo [Revonsuo, A. (2000). The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences, 23(6), 877-901]. Our findings suggest the terrorist attacks had a tangible impact on the content of many people's dreams, but did not fundamentally alter the cognitive processing features of their dreaming. The 9/11 attacks affected what they dreamed about, but not the way they dreamed.     

Frequency of lucid dreaming in a representative German sample

Lucid dreams occur when a person is aware that he is dreaming while he is dreaming. In a representative sample of German adults (N = 919), 51% of the participants reported that they had experienced a lucid dream at least once. Lucid dream recall was significantly higher in women and negatively correlated with age. However, these effects might be explained by the frequency of dream recall, as there was a correlation of .57 between frequency of dream recall and frequency of lucid dreams. Other sociodemographic variables like education, marital status, or monthly income were not related to lucid dream frequency. Given the relatively high prevalence of lucid dreaming reported in the present study, research on lucid dreams might be pursued in the sleep laboratory to expand the knowledge about sleep, dreaming, and consciousness processes in general.     

Another look at dreaming: disentangling Freud's primary and secondary process theories

The Interpretation of Dreams contains Freud's first and most complete articulation of the primary and secondary mental processes that serve as a framework for the workings of mind, conscious and unconscious. While it is generally believed that Freud proposed a single theory of dreaming, based on the primary process, a number of ambiguities, inconsistencies, and contradictions reflect an incomplete differentiation of the parts played by the two mental processes in dreaming. It is proposed that two radically different hypotheses about dreaming are embedded in Freud's work. The one implicit in classical dream interpretation is based on the assumption that dreams, like waking language, are representational, and are made up of symbols connected to latent unconscious thoughts. Whereas the symbols that constitute waking language are largely verbal and only partly unconscious, those that constitute dreams are presumably more thoroughly disguised and represented as arcane hallucinated hieroglyphs. From this perspective, both the language of the dream and that of waking life are secondary process manifestations. Interpretation of the dream using the secondary process model involves the assumption of a linear two-way "road" connecting manifest and latent aspects, which in one direction involves the work of dream construction and in the other permits the associative process of decoding and interpretation. Freud's more revolutionary hypothesis, whose implications he did not fully elaborate, is that dreams are the expression of a primary mental process that differs qualitatively from waking thought and hence are incomprehensible through a secondary process model. This seems more adequately to account for what is now known about dreaming, and is more consistent with the way dream interpretation is ordinarily conducted in clinical practice. Recognition that dreams are qualitatively distinctive expressions of mind may help to restore dreaming to its privileged position as a unique source of mental status information.     

Psychoanalytic dream theory and recent neurobiological findings about REM sleep

I have reviewed Hobson and McCarley's activation-synthesis hypothesis of dreaming which attempts to show that the instigation and certain formal aspects of dreaming are physiologically determined by a brainstem neuronal mechanism, their reasons for suggesting major revisions in psychoanalytic dream theory, and neurophysiological data that are inconsistent with their hypothesis. I then discussed the concept of mind-body isomorphism pointing out that they use this concept inconsistently, that despite their denials they regularly view physiology as primary and psychological processes as secondary, and that they frequently make the error of mixing the languages of physiology and psychology in their explanatory statements. Finally, in order to evaluate Hobson and McCarley's claim that their findings require revision of psychoanalytic dream theory, I examined their discussions of chase dreams, flying dreams, sexual dreams, the formal characteristics of dreams, the forgetting of dreams, and the instigation of dreams. I concluded that although their fascinating physiological findings may be central to understanding the neurobiology of REM sleep, they do not alter the meaning and interpretation of dreams gleaned through psychoanalytic study.     

Intentionality Analysis and the Problem of Self and Other

Dennett recounts an alarm clock dream which he experienced as taking a long time even though the alarm presumably sounded for only a short time. His explanation of this paradoxical behavior of time in dreams is that there actually is no dream experience but that unexperienced dreams are composed directly into memory banks and are subsequently played back on awakening. I critique Dennett's theory of dreams in Heideggerian terms on the grounds that he takes temporality in a common-sense superficial way. I review Heidegger's theory of time and using Dennett's own dream show that “temporality temporalizes itself' in dreams too as a free production of dreaming Dasein. Dream time is what dreaming temporality produces whatever the clocks of waking show, and is entirely consistent with authentic dream experience. An appreciation of the process of dreaming temporality temporalizing itself supports Heidegger's concept of temporality as an a priori of Dasein's Being.