Theoretical models explaining bad dreams and nightmares
Alexandre Lemyre, M.A., Ph.D.
The content of this article was last updated on February 1, 2022.
Introduction
Why do some people experience bad dreams and nightmares? Why do nightmares sometimes come and go, being rare or absent for weeks, months, or years, before reappearing? It is one thing to try identifying the causes (or “triggers”) of nightmares, it is another to explain the psychological processes through which events, affective states, or mental states lead to nightmares. To be honest, I am unsatisfied with the current state of our understanding of the etiology (the development and maintenance) of nightmares. In most cases, the causal psychological processes that have been suggested are unclear/unspecific, untested (i.e., scientific evidence supporting these processes is lacking or inexistent), or both. Nevertheless, some intriguing theories and hypotheses have been put forward, and I will review them in the present post.
The work of Dr Tore Nielsen and his collaborators
In 2021, Dr Tore Nielsen is full professor at the University of Montreal and director of the Dreams and Nightmares Laboratory. He has contributed to three complementary theoretical models of nightmares, namely, the affect network dysfunction model (Levin and Nielsen, 2007), the stress acceleration hypothesis (Nielsen, 2017), and the differential susceptibility framework (Carr & Nielsen, 2017). The latter two theories may be viewed as complementary to (and to some extent, overlapping with) the affect network dysfunction model.
The Affect Network Dysfunction (AND) model
If a person has a dog phobia and exposes themselves to a dog (first approaching it, then petting it) in a safe context (that is, with no risk of being attacked by the dog), a phenomenon of “habituation” will occur. That is, the longer the person remains in the presence of the dog, the less intense their fear will be. If the person repeats this exercise multiple times in multiple contexts (i.e., with different dogs and in different environments), the fear of dogs itself will eventually “extinguish”. That is, the person would experience little or no fear when exposed to other non-threatening dogs in the future. This is what is called “fear extinction”. This does not only work with dogs, but with any animal, person, object, or situation that triggers fear without being avoided, and without causing actual psychological or physical harm. There is more to it, but in short, this process of fear extinction is the basis of exposure therapy for anxiety disorders (Moscovitch et al., 2009).
In their seminal theoretical paper, Levin and Nielsen (2007) proposed that dreaming serves a fear extinction function. More precisely, dreams would incorporate fear-inducing stimuli (memories of objects, animals, persons, or situations that trigger fear) together with a safe dream context. Because the dreamer is exposed to the fear-inducing stimuli without being harmed, habituation would occur (i.e., the dreamer’s fear would decrease). As a result, the individual would experience less fear toward these stimuli in waking (Levin & Nielsen, 2007). You might see this process as a form of exposure therapy in your dreams. One limitation of this theory is that it does not explain the function of dreams featuring no emotion or emotions other than fear/anxiety (especially, positive emotions; Weiss, 2007). For instance, at least one third of all recalled dreams that are experienced when sleeping at home have a primarily positive emotional valence (Röver & Schredl, 2017; Schredl & Doll, 1998; Sikka et al., 2017). For more information on that, feel free to read another post on emotions in dreams.
According to Levin and Nielsen (2007), the proposed function of dreaming would not work in the case of nightmares. Nightmares would be more likely to occur when individuals are high in affect distress and in affect load. Affect distress is a tendency to react to stressful situations with heightened negative emotions (in other words, the individual is more sensitive), whereas affect load is the accumulation of all the stressors experienced by the individual. High affect distress and high affect load would lead to an hyperactivation of the amygdala (a central part of the brain involved in the production of emotions, especially fear) and an under‑activation of the prefrontal cortex, which is involved in the regulation of emotions. This brain state would prevent the dream from incorporating a safe context along with the fear-inducing stimuli, leading to the experience of a nightmare. Habituation toward the fear-inducing stimuli could not occur in the nightmare.
In summary, nightmares would constitute a failure of the normal function of dreaming – the extinction of fears – caused by high affect distress and high affect load. This view has gained substantial recognition in recent years, as reflected by its incorporation in a model of nightmare etiology authored by several well-known sleep and dream researchers (Gieselmann et al., 2019). However, based on the current state of the dream literature, I believe it is way too early to conclude that the function of dreaming is to extinguish fears, or that nightmares constitute a failure to fulfill this function. In fact, most psychological processes hypothesized by this theory (e.g., habituation to the fear-inducing stimuli in dreams, subsequent reduction of the fear response toward these fear-inducing stimuli in waking) have not been directly tested. This is an issue I discussed in my doctoral thesis (Lemyre, 2021, pp. 37-42; written in French).
The Stress Acceleration Hypothesis
Some nightmares are not clearly linked to a specific traumatic event: these are called idiopathic nightmares. Nielsen (2017) suggests that, just as posttraumatic nightmares are linked to previous traumas, idiopathic nightmares may result from adverse experiences early in life. In that sense, the “trigger” for posttraumatic nightmares and for idiopathic nightmares would be the same: distressing life experiences. In the case of posttraumatic nightmares, these experiences are remembered and traumatic in nature, but in the case of idiopathic nightmares, the distressing experiences would have happened too early in life to be remembered (i.e., during the infantile amnesia period, up to about 3.5 years old) or would not meet the common definition of a traumatic event (for example, maternal separation, moderate forms of neglect, inconsistent parental rules, or even dethronement by the birth of a sibling; Nielsen, 2017).
Nielsen (2017) goes further by proposing the “stress acceleration hypothesis of nightmares”. According to this hypothesis, distressing experiences early in life would: 1) shorten the infantile amnesia period, so that distressing memories that would otherwise be forgotten will be recalled, and 2) increase the propensity for fear learning, which means that the individual would more easily develop fear reactions toward persons/objects/situations that are associated with negative experiences. A better recall of infantile distressing memories and a greater propensity for fear learning would increase the likelihood of experiencing nightmares later in life (Nielsen, 2017).
The Differential Susceptibility Framework
According to this model, individuals who experience frequent nightmares are higher on a trait called Sensory Processing Sensitivity (SPS). SPS is a general propensity to experience stronger positive and negative emotional reactions, which would lead to a deeper processing of information, a greater awareness of environmental subtilities (including others’ emotional state), and a tendency to feel overwhelmed when stimuli are too strong. Individuals who are high in SPS react more strongly both to positive and negative life conditions, producing “for better and for worse” outcomes. Specifically, for individuals high in SPS, positive life conditions would lead to curiosity and reward‑seeking, pleasant daydreams, prosocial behaviors and empathy, and ultimately, vivid and powerful positive dreams. In turn, these dreams would favor hopefulness and excitement in waking. On the dark side of this spectrum, for individuals high in SPS, negative life conditions would lead to a feeling of being threatened, attentional narrowing toward threat‑relevant information, and waking distress, which would ultimately lead to nightmares. In turn, these nightmares would promote helplessness and anxiety in waking. This is not to say that these chains of events never occur for individuals who are lower in SPS, but simply that they would occur more frequently and/or more intensely for individuals high in SPS. To summarize, the differential susceptibility framework suggests that individuals who are high in SPS tend to experience more vivid and positive dreams in positive life conditions, but also tend to experience more bad dreams and nightmares in negative life conditions (Carr & Nielsen, 2017).
Linking nightmares to the proposed emotion regulation function of dreaming
Theories attributing an emotion regulation function to dreaming
There is excellent evidence showing that sleep allows the formation of new connections in memory (Diekelmann & Born, 2010; Feld & Born, 2017; Lewis & Durrant, 2011; Rasch & Born, 2013; Stickgold & Walker, 2013; Walker & Stickgold, 2010). It has been suggested that the formation of these new connections might be reflected in dreams. Some researchers even suggest that dreaming is causally involved in the memory processes that occur during sleep (Wamsley, 2014). According to the theories of Hartmann (2011), Malinowski and Horton (2015), and Cartwright (2011), the formation of new connections between newer and older emotional memories during sleep – which would either be reflected in dreams or caused by dreams – reduces negative emotional reactivity in waking. That is, the person would experience reduced negative emotions in general and/or in reaction to specific stimuli or situations. Unfortunately, at a theoretical level, how the formation of new connections in memory during sleep/dreams is expected to lead to emotion regulation in waking remains quite unclear, or at least, unspecific. For that reason, I will not elaborate on that topic.
Posttraumatic nightmares and emotion regulation
According to Hartmann (1996, 1998, 2007, 2011), posttraumatic nightmares are the best examples of dreams that fulfill their emotion regulation function. Specifically, these nightmares would form connections between the memories of the traumatic event and long-term memory networks, which would contribute to the reduction of posttraumatic stress disorder (PTSD) symptoms and favor resilience toward future distressing events. Unfortunately, this view is difficult to reconcile with the negative consequences of nightmares, which can include a reduction in sleep quality and quantity, fatigue, lack of concentration, negative post-sleep emotions, and impairments in major area of functioning (Köthe & Pietrowsky, 2001; Lemyre et al., 2019; Pietrowsky & Köthe, 2003). The hypothesized therapeutic effect posttraumatic nightmares is also difficult to reconcile with evidence suggesting that nightmares contribute to the development and persistence of PTSD symptoms (Spoormaker & Montgomery, 2008). For instance, the experience of nightmares prior to a military deployment (which involves a high risk of exposure to traumatic events) positively predicts the experience of PTSD symptoms at six months post-deployment (van Liempt et al., 2013). Moreover, a review of treatment studies showed that imagery rehearsal therapy – an effective psychological treatment for nightmares – reduces PTSD symptoms, suggesting an involvement of nightmares in the maintenance of these symptoms (Casement & Swanson, 2012). It should be noted, however, that a more recent study comparing two treatment groups (imagery rehearsal therapy + cognitive behavioral therapy for PTSD VS cognitive behavioral therapy alone) did not support the role of nightmares in the maintenance of PTSD (Belleville et al., 2018). Overall, in my understanding, the hypothesis of a therapeutic effect of nightmares on PTSD symptoms remains largely unsupported.
Nightmares as a failure to form new connections
When presenting their respective theories, Malinowski and Horton (2015), and Cartwright (2011) took the opposite stance by suggesting that nightmares constitute a dysfunction of normal dreaming. According to Cartwright (2011), nightmares that cause awakening interrupt dreaming, preventing it from fulfilling its emotion-regulation function. Unfortunately, the psychological processes responsible for the experience of nightmares (which should be differentiated from the events or affective states that trigger nightmares) are not clear/specific.
Malinowski and Horton (2015) offers a partial, yet interesting explanation for some nightmares. According to these authors, the same processes that are involved in generating mental imagery (i.e., the capacity to imagine hypothetical events and to remember one’s own past) are also involved in the production of dreams. When the capacity to generate mental imagery is impaired, as can be the case following a traumatic experience, dream production would also be affected. When this occurs, dreams would be less hyper-associative. Concretely, instead of experiencing new and creative dreams (i.e., hyper-associative dreams), the individual would experience posttraumatic nightmares that are replicative (i.e., that resemble the actual trauma) and possibly repetitive (Malinowski & Horton, 2015). One downside of this explanation is that it cannot be applied to idiopathic nightmares (i.e., nightmares that are not clearly associated with a traumatic experience), which can be as new and creative as regular dreams. Nonetheless, the explanation of Malinowski and Horton (2015) might help explain the effectiveness of imagery rehearsal therapy in reducing nightmare frequency (Morgenthaler et al., 2018). Indeed, imagery rehearsal therapy involves practicing mental imagery skills (Krakow & Zadra, 2010), which may help the brain recover its ability to produce new and creative dreams (i.e., hyper-associative dreams) that would replace the replicative/repetitive posttraumatic nightmares.
Evolutionary Theories of Dreaming
Some contemporary theories of the function of dreaming are anchored in evolutionary psychology. These theories build on the premise that the genes responsible for the experience of dreams were favored by natural selection because dreaming served a biologically adaptive function. By “biologically adaptive function”, I mean any function that would have increased the fitness of our ancestors. Here, “fitness” refers to the capacity of an organism to survive and reproduce (this is a simplified definition, but it suffices for now), whereas “our ancestors” refers to whatever species in which the capacity of dreaming first appeared. These ideas can be summarized in one simplified sentence: “Evolutionary theories of the function of dreaming assume that modern humans have the ability to dream because that ability increased our ancestors’ fitness, that is, their capacity to survive and reproduce.”
Because the only reliable way to study dreaming is through self-reports, there is no way of knowing with certainty whether species other than humans (e.g., cats, dogs, mouse, etc.) also experience oneiric activity that may be defined as dreaming. Consequently, any hypothesis on the evolutionary origin of dreams is largely speculative. Dreaming could have first evolved in our human ancestors (Domhoff, 2018, pp. 264-265; Foulkes, 2017), in a common ancestor to all mammals (humans being one of many mammalian species), or in an even more distant ancestor (Manger & Siegel, 2020; Murkar & Kamal, 2015).
If dreaming did increase fitness in our ancestors (i.e., our human ancestors or our more distant ancestors), those individuals who had the ability to dream would have had more offspring compared with the other members of their species. Their offspring would have been more likely to have the “dream genes” (i.e., the genes responsible for the ability to dream), and in turn, they would have had more dream-proficient offspring of their own. Over many generations, the ability to dream would have generalized in that species’ population. It would then have been transmitted over a great many generations until modern humans inherit it. It is worth noting that the nature of dreams may have evolved/changed considerably during this process. Finally, although it is postulated that dreaming was adaptive in our ancestor’s environment (in relation to fitness), there is no claim that it is still adaptive in our modern – hugely transformed – environment.
The Threat Simulation Theory
According to the threat simulation theory proposed by Revonsuo (2000), dreaming specializes in simulating threats that are relevant to survival. By doing so, dreams would offer an opportunity to practice avoidance skills, which would be useful to face real dangers in waking. A central claim of this theory is that encountering real threats in waking activates the “threat simulation system”, which would result in more threatening dreams. This would explain why traumatic events tend to be followed by posttraumatic nightmares. In summary, by featuring dangers, bad dreams and nightmares would serve a specific function: to practice danger-avoidance skills (Revonsuo, 2000). While this function would have been useful for our ancestors living in their natural environment, it may not (always) be useful in our modern environment.
Studies that have tested the threat simulation theory have obtained mixed results. When university students use a dream diary to report dreams experienced while sleeping at home, between 35% and 77% of these dreams contain at least one threat. Examples of dream threats are being pursued, experiencing an accident or a misfortune, failing to achieve an important goal, experiencing a catastrophe, having a disease or another medial problem, or being the victim of a verbal or physical threat/aggression. Between 44% and 63% of the threats in these dreams are realistic, whereas the other threats (37-56%) are realistic but unlikely to occur in waking, unrealistic, or unclassifiable (Mathes & Schredl, 2016; Revonsuo & Valli, 2000; Valli et al., 2007). Other studies in which university students reported their most recent dreams have shown that only 8-13% of dreams feature realistic life-threatening events (Malcolm-Smith & Solms, 2004; Malcolm-Smith et al., 2008). Also using the “most recent dream method”, Malcolm-Smith et al. (2012) observed that 73% of dreams feature approach behaviors in response to the central dream event; avoidance behaviors were predominant in only 27% of dreams. To summarize, while threats are more common in dreams than in waking life, realistic threats in dreams – especially those that threaten the dreamer’s life – remain quite rare.
What may be the function of dreams that do not contain (realistic) threats? According to the social simulation theory developed by Revonsuo et al. (2015), dreams could simulate social situations. By doing so, dreams would allow to practice cognitive skills, such as recognizing the affective states of others. Practicing these skills in dreams would have helped our human ancestors to navigate their social environment in waking. According to these authors, skills that facilitate social interactions and cooperation would have been as useful as danger‑avoidance skills to survive and reproduce in a natural environment (Revonsuo et al., 2015; Tuominen, Revonsuo, et al., 2019). The vast majority of dreams contain human characters (Domhoff, 1996, chapitre 4) and social interactions are more common in dreams than in waking life (McNamara et al., 2005; Tuominen, Stenberg, et al., 2019), which supports the social simulation theory. Relatedly, dreams rarely feature day-to-day activities such as reading, writing, or arithmetic (Hartmann, 2000), which are usually solitary activities. Finally, it is worth highlighting that there is uncertainty about the function of dreams and nightmares that feature threatening human characters: whether these dreams would serve a threat simulation function, a social simulation function, or both is unclear.
The Costly Signaling Theory
McNamara and Szent-Imrey (2007) proposed a “costly signaling theory” of dreaming, which is also anchored in evolutionary psychology. More specifically, it is anchored in sexual selection theory, which proposes that costly signals (i.e., signals that are hard to fake, such as antlers on a deer) are associated with fitness-promoting genes and serve to communicate (advertise) the presence of those genes. These authors suggest that an intense rapid eye movement sleep (i.e., the sleep stage most strongly associated with the experience of dreams), negatively valenced dreams, and the resulting disturbed mood in waking could serve as a costly signal. The resulting bad mood in waking, or the ability to thrive despite an impaired mood, would be interpreted by others as signaling the presence of good genes, therefore increasing one’s opportunities to form/strengthen social bonds and to find a mate. At the very least, a bad mood in waking could trigger others’ empathy and/or motivate them to lower their psychological defenses, facilitating collaborations (McNamara & Szent-Imrey, 2007). Personally, I still have difficulty to fully grasp this theory because it contains several propositions that are not always related to one another in a clear way.
The Feeling Priming Theory
Throughout the years, several well-known researchers in the field of dream research have suggested that concerns influence dreaming (Domhoff, 1996, 2011; Hartmann, 1996, 2011; Schredl, 2003, 2015). For instance, pregnant women dream of pregnancy, childbirth, and motherhood more often than women who are not pregnant (Dagan et al., 2001; Lara-Carrasco et al., 2013; Nielsen & Paquette, 2007; Sabourin et al., 2018), women in the process of divorce sometimes dream about their ex-spouse (Cartwright et al., 2006), individuals in bereavement sometimes dream about the person they lost (Barrett, 1992; Black et al., 2019), many individuals with a substance use disorder experience drug dreams during periods of abstinence (Colace, 2014; Johnson, 2012), and a large proportion of students who anticipate an important exam dream about it (Arnulf et al., 2014).
In the context of my doctoral thesis, my supervisors and I developed the feeling priming theory of dreaming (Lemyre et al., 2022). According to this theory, only future-oriented concerns influence dreams. These future-oriented concerns are divided in two types: gratifying anticipated events (i.e., anticipated events that are susceptible to bring pleasure) and aversive anticipated events (i.e., anticipated events that are susceptible to bring displeasure).
According to the feeling priming theory, dreams would reproduce the anticipated feelings that are associated with our anticipated events. An anticipated feeling is a feeling that we anticipate experiencing in the future in reaction to an aversive or a gratifying event. For instance, if you anticipate experiencing pride (the anticipated feeling) in the event of succeeding your incoming driving exam (the gratifying anticipated event), you might experience a positive dream that reproduces this feeling of pride. Likewise, if you anticipate experiencing a mixed feeling of disappointment and shame (the anticipated feeling) in the event of being fired from your work (the aversive anticipated event), you might experience a negative dream that reproduces this feeling of disappointment/shame. It is worth noting that most anticipated feelings would be reproduced by dream scenarios that share little or no similarity with the actual anticipated events. For instance, in the above example, the dream scenario that reproduces the feeling of disappointment/shame could be unrelated to your work.
The anticipated feelings that have been reproduced in the dreams (“pride” or “disappointment/shame” in the examples above) would remain primed in memory after awakening and during the day. This would, in turn, favor the degree of hope/desire experienced toward the gratifying anticipated events (e.g., succeeding on the driving exam in the example above) and the degree of fear experienced toward aversive anticipated events (e.g., being fired in the example above). As a result, the person would be more motivated to approach the gratifying anticipated events (e.g., practicing more in preparation to the driving exam) and to avoid the aversive anticipated events (e.g., putting more time and energy in one’s work to avoid being fired). It is suggested that this pattern of increased approach behaviors (for gratifying anticipated events) and avoidance behaviors (for aversive anticipated events) would have favored the fitness of our ancestors living in their natural environment.
In summary, all negatively valanced dreams, including bad dreams and nightmares, would serve to reproduce negative anticipated feelings associated with aversive anticipated events. This, in turn, would favor fear toward these aversive anticipated events in waking, increasing the motivation to adopt avoidance behaviors. An interesting implication of the feeling priming theory is that traumas would result in posttraumatic nightmares only when they create new aversive anticipated events (i.e., negative expectancies in relation to the future) or exacerbate existing ones.
Summary and Conclusion
There are several theoretical explanations for the experience of bad dreams and nightmares. Many of these explanations are mutually exclusive (i.e., irreconcilable with one another). On the one hand, nightmares have been described as a dysfunction of so-called “normal dreaming”, although the nature of the proposed dysfunction varies across theories. On the other hand, nightmares (and negative dreams more generally) have been hypothesized to serve a biologically adaptive function that would have favored the fitness of our ancestors. It is worth highlighting that most theoretical models explaining bad dreams and nightmares build on the premise that dreaming is functional in the first place. In fact, whether dreaming is functional is still highly debated among dream researchers. For instance, in his book, Domhoff (2018) argues against the existence of any function of dreaming. My understanding is that the scientific evidence does not yet allow to determine whether dreaming is functional, something that has been discussed by Springett (2019). In any case, developing a better understanding of nightmare etiology remains paramount to the development of new (and hopefully, highly effective) psychological treatments targeting this sleep difficulty.
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