An Important Exception
Thus far, we have been careful to use qualifiers such as “generally” and “a majority of the time”, when referring to the situated nature of dream cognition because it is possible to have waking-like cognition operate while dreaming (Laberge et al., 1981). This phenomenon is known as lucid dreaming and occurs when the dreamer realizes, within the dream, that they are dreaming and that their actual body is asleep in bed. With this knowledge in mind, the dream continues and the dreamer is able to manipulate and interact within the dream world from a waking frame of consciousness. Research has shown that people are able to reach this state in a sleep laboratory and are able to indicate their lucidity to the waking world by giving distinct eye signals that are recorded by EOG (LaBerge et al., 1986). Upon waking, a dream report is given in which the subject describes how many eye movements they made and the duration between these eye movements. These reports are shown to match up with observed physiological data (Laberge et al., 1981).
This is a capacity that we contend has to be unique to humans, and represents a level of awareness that is often not attained in the waking state (although see Hegel for talk of a similar type of waking “self-consciousness”; Hegel, 1979). While lucid dreaming occurs rarely for people in the general population, it is a skill that can be learned through various techniques (Laberge, 1980). These techniques generally have the person become more aware of their state of consciousness and question their reality throughout the day. By forcing the person to step outside the flow of their current perceptions and motivations during waking life, there is an increased chance that this will occur during dreaming and facilitate a lucid dream. This allows a kind of feedback between the dreaming and waking state to be reached where a more unsituated approach to waking life affects the level of situatedness in the dream and vice versa. Thus, a by-product of the dreaming virtual-rehearsal mechanism may be the ability to obtain a higher level of awareness of one’s place in regards to one’s surroundings.
Since higher mental operations can occur during dreams, this is surely bound to interact and feed into waking cognitive abilities, and while it might not confer an obvious benefit to fitness, dreams are a venue that have been used in a number of cultures to attain higher states of consciousness (e.g., Tibetan dream yoga, and the practices of the Senoi) and increase one’s sense of well-being (Wangyal, Rinpoche, and Dahlby, 1998). Since no neuroimaging work has been done with lucid dreaming one can only speculate, but it is possible that people who are frequent lucid dreamers would show a different functional pattern of activation while in REM sleep, with greater activation of frontal regions. This potential difference in activation for lucid dreamers demonstrates the importance of taking into account subjective dream reports when interpreting data on the physiology of sleep in general, and REM sleep in particular.
Saturday, August 28, 2010
Dream Ontogeny
Dream Ontogeny
While the social aspects of dreaming offer insight into the socio-developmental benefits of dreams, so does an examination of the ontogeny of sleep and dreaming. Multiple facets of our mental development are ontogenetically scheduled (Bertenthal, 1996). For example, at about nine months of age it is apparent that infants acquire the new skill of treating others as intentional beings (Trevarthen, 1979). Other mental capacities also begin to develop within a predictable timeline, a universal characteristic of the human species and occurring independent of culture. Likewise, the architecture of sleep cycles follows a specific ontogeny that is consistent to humans as a species (Frank and Heller, 2003).
REM sleep occurs most frequently in newborns, and decreases throughout the lifespan. Newborns can spend about eight hours a day in REM sleep, and REM sleep actually occurs at sleep onset (Winson, 2002). In contrast, as we age, sleep onset is characterized by stages of NREM sleep, followed by REM sleep in less amounts. By the age of three, REM sleep is reduced to about three hours a day and continues to decline throughout the lifespan.
Why is REM sleep such a prominent brain state in the developing brain? One answer to this question follows from the previous argument as to the potential function of dreams, i.e., a virtual rehearsal mechanism. It is well known that children, and even other species, suffer detrimental effects when raised in impoverished environments (Joseph, 1999). The converse is also true. Infants raised in environments with rich amounts of information show increased cognitive skills at an earlier age, and this can even extend throughout the lifespan (Diamond, 1988); an enriched environment during the development of the nervous system optimizes its functionality.
As mentioned above, all evidence points toward the notion that virtual environmental stimuli are treated in essentially the same way as real stimuli from the environment. Therefore, it would make adaptive sense for an organism that is young and still developing to experience the most rich and vivid environment possible. If this is experienced in infant dreams, then this is exactly what has been selected for, as newborns spend a good deal of time in this virtual environment.
Of course, the virtual environment will likely be a reflection of the real environment and how infants interact with their virtual environment is going to be a function of the perceptual and cognitive capacities they have developed. So, the REM mentation of infants, which we are arguing constitutes a type of dreaming, probably consists of recreations with important sensory information that is taken in while awake. It is this information, and these interactions with the physical and social world, which is likely vital in shaping the future mental development of the child.
The brain connections that are thought to be developed during REM sleep are not going to be haphazardly put into place and subsequently strengthened, rather, through dreaming, these connections may be optimized based on experience. If mental rehearsal can induce change and lead to the reorganization of the brain in relatively short periods of time (Pascual-Leone et al., 1995), surely the cumulative time spent dreaming will impact brain development as well. While this argument may seem contradictory to data indicating that dreaming is a gradual cognitive process that does not take place regularly until around ages 5-9 (Foulkes, 1999), the dream experience is bound to be tightly coupled with the development of general mental abilities including perception, language, and memory. Further, the lack of verbal dream reports should not exclude, a priori, the possibility that a form of a dreaming is taking place.
Hypotheses can be generated based on the notion that infants have a type of dreaming mechanism, and this dreaming mechanism influences the development of certain cognitive abilities. Specifically, we predict that an optimal environment that has a good deal of complexity will interact with a healthy sleep schedule to cause an optimal development of intellectual capacities. Conversely, a disruption in the normal REM cycle of a developing individual could have negative consequences on the development of mental functions. An example of a disorder where this hypothesis could be investigated is autism. Autism has been likened to a TOM deficit and is associated with disrupted sleep patterns (Richdale and Prior, 1995). Based on the theory developed in this paper, it is predicted that a portion of the deficits observed in autistics is due to their lack of REM sleep. We theorize that through an inability to dream, the autistic brain is negatively affected and through this negative effect, so are subsequent behaviors, such as interactions with the world around them.
While the social aspects of dreaming offer insight into the socio-developmental benefits of dreams, so does an examination of the ontogeny of sleep and dreaming. Multiple facets of our mental development are ontogenetically scheduled (Bertenthal, 1996). For example, at about nine months of age it is apparent that infants acquire the new skill of treating others as intentional beings (Trevarthen, 1979). Other mental capacities also begin to develop within a predictable timeline, a universal characteristic of the human species and occurring independent of culture. Likewise, the architecture of sleep cycles follows a specific ontogeny that is consistent to humans as a species (Frank and Heller, 2003).
REM sleep occurs most frequently in newborns, and decreases throughout the lifespan. Newborns can spend about eight hours a day in REM sleep, and REM sleep actually occurs at sleep onset (Winson, 2002). In contrast, as we age, sleep onset is characterized by stages of NREM sleep, followed by REM sleep in less amounts. By the age of three, REM sleep is reduced to about three hours a day and continues to decline throughout the lifespan.
Why is REM sleep such a prominent brain state in the developing brain? One answer to this question follows from the previous argument as to the potential function of dreams, i.e., a virtual rehearsal mechanism. It is well known that children, and even other species, suffer detrimental effects when raised in impoverished environments (Joseph, 1999). The converse is also true. Infants raised in environments with rich amounts of information show increased cognitive skills at an earlier age, and this can even extend throughout the lifespan (Diamond, 1988); an enriched environment during the development of the nervous system optimizes its functionality.
As mentioned above, all evidence points toward the notion that virtual environmental stimuli are treated in essentially the same way as real stimuli from the environment. Therefore, it would make adaptive sense for an organism that is young and still developing to experience the most rich and vivid environment possible. If this is experienced in infant dreams, then this is exactly what has been selected for, as newborns spend a good deal of time in this virtual environment.
Of course, the virtual environment will likely be a reflection of the real environment and how infants interact with their virtual environment is going to be a function of the perceptual and cognitive capacities they have developed. So, the REM mentation of infants, which we are arguing constitutes a type of dreaming, probably consists of recreations with important sensory information that is taken in while awake. It is this information, and these interactions with the physical and social world, which is likely vital in shaping the future mental development of the child.
The brain connections that are thought to be developed during REM sleep are not going to be haphazardly put into place and subsequently strengthened, rather, through dreaming, these connections may be optimized based on experience. If mental rehearsal can induce change and lead to the reorganization of the brain in relatively short periods of time (Pascual-Leone et al., 1995), surely the cumulative time spent dreaming will impact brain development as well. While this argument may seem contradictory to data indicating that dreaming is a gradual cognitive process that does not take place regularly until around ages 5-9 (Foulkes, 1999), the dream experience is bound to be tightly coupled with the development of general mental abilities including perception, language, and memory. Further, the lack of verbal dream reports should not exclude, a priori, the possibility that a form of a dreaming is taking place.
Hypotheses can be generated based on the notion that infants have a type of dreaming mechanism, and this dreaming mechanism influences the development of certain cognitive abilities. Specifically, we predict that an optimal environment that has a good deal of complexity will interact with a healthy sleep schedule to cause an optimal development of intellectual capacities. Conversely, a disruption in the normal REM cycle of a developing individual could have negative consequences on the development of mental functions. An example of a disorder where this hypothesis could be investigated is autism. Autism has been likened to a TOM deficit and is associated with disrupted sleep patterns (Richdale and Prior, 1995). Based on the theory developed in this paper, it is predicted that a portion of the deficits observed in autistics is due to their lack of REM sleep. We theorize that through an inability to dream, the autistic brain is negatively affected and through this negative effect, so are subsequent behaviors, such as interactions with the world around them.
Social Cognition in Dreams
Social Cognition in Dreams
While the dorsolateral prefrontal cortex appears to be inhibited during REM, there is not a uniform deactivation of the frontal regions in the brain during states of dreaming. For example, there is a consistent increase in activity of the anterior cingulate in REM sleep (Braun et al., 1997). The anterior cingulate is a medial frontal region implicated in such functions as decision-making, conflict resolution, social cognition, and social judgment tasks which probe a subject’s theory of mind (TOM) and requires subjects to take into account the intentions and mental states of others (Devinsky, Morrell, Vogt, 1995). In fact, recent studies link activation of the anterior cingulate with capacities of a TOM module (Vogeley et al., 2001). These data suggest that aspects of cognition centering on the processing of social information are strongly activated during REM sleep.
This is particularly interesting since it is thought that our complex social interactions and the information processed in the social domain played an integral role in the development of primate’s mental capacities (Whiten and Byrne, 1988). If these pathways are active during REM sleep and this type of information is being rehearsed, then it should function to effectively strengthen the effects that processing of social information has on mental development. Further supporting this role is the tendency for a large proportion of dreams to contain other people and represent various social situations (Kahn et al., 2002).
Another example of a skill that has arguably played a pivotal role in other functional aspects of the human intellect and could serve to be shaped by dreaming is that of interpretation. As discussed by Bogdan (1997, p.108), “…key advances in interpretation, such as the recognition of belief, were accelerated by increased opportunities to interact with or manipulate subjects and slowed down by a lack of such opportunities.” As such, via teasing, play, mental rehearsal/imagery, or dreaming, the individual is given the opportunity to utilize successful strategies in dealing with these situations and further develop interpretive skills. In fact, studies of children’s dream-reports indicate that their dreams more often contain family members and close friends than adults’ dreams (Hobson, 1988), possibly due to the fact that it is more important for younger children to be practicing close interpersonal skills than it is for adults.
It, however, could be argued that the rehearsal of social situations would not play a significant role in increasing one’s fitness. In order to address this claim, it is necessary to comment on the potential benefits of being socially sophisticated. First, in terms of pure survival value, those individuals who best interact with those around them, i.e., those who interact without interpersonal conflict and confrontation, will likely have better access to resources in their social group, be it mates or food (Foley, 1989). There is wide variation between cultures in the types of traits that render an individual fit, and what makes humans a successful species is that our ability to deal with the social environment that we are thrust into is not completely pre-wired (Sapir, 1921; Whorf, 1956). Those individuals that could use feedback from the environment to effectively modify their social interactions would be best off, as individual groups often have particular social nuances. Also, clearly in our own species, the traits we have which help us deal with social situations vary greatly and under certain circumstances can be beneficial, while at other times potentially put us at risk. Due to the variable fitness of particular behaviors at particular times, we need to be adept at interpreting cultural standards when interacting with others. For example, one cultures “alpha male” could potentially be ostracized in another culture. This newly ostracized individual would be less likely to obtain mates, and would be less competitive for the resources that would influence his survival. Therefore, something that could tip the scale in allowing someone to best deal with important social interactions would likely be selected for over time.
Flanagan (2000) raises the potential criticism that dreams do not give us an accurate representation of ourselves and conspecifics, positing that there is no advantage conferred in dreams by rehearsing various social interactions. He claims that the development of a TOM module based on dreamed social interactions would be flawed, and that accurate depictions of others and ourselves is the exception rather than the rule while dreaming. While we do not disagree that in dreams ourselves and others often act in a surprising and atypical manner, overall our representation of those we know is quite impressive and accurate. From their visual appearance, to the tone of voice, to the style of speaking, by virtue of the fact that we recognize and interact with those we know in the dream-world, we have an amazing ability to unconsciously recreate dream characters from those people with which we typically interact (above and beyond any verbal description that we could give of that person). While we surely cannot say a dream character’s behavior is how that person would act in ‘real life,’ we also know that there is no way to accurately predict how that person will behave when encountering a new situation in real life. In waking life, the best that we can do is interpret overt cues and then attempt to understand a person’s intentions and predict their actions, for which dreams offer such a venue.
While the dorsolateral prefrontal cortex appears to be inhibited during REM, there is not a uniform deactivation of the frontal regions in the brain during states of dreaming. For example, there is a consistent increase in activity of the anterior cingulate in REM sleep (Braun et al., 1997). The anterior cingulate is a medial frontal region implicated in such functions as decision-making, conflict resolution, social cognition, and social judgment tasks which probe a subject’s theory of mind (TOM) and requires subjects to take into account the intentions and mental states of others (Devinsky, Morrell, Vogt, 1995). In fact, recent studies link activation of the anterior cingulate with capacities of a TOM module (Vogeley et al., 2001). These data suggest that aspects of cognition centering on the processing of social information are strongly activated during REM sleep.
This is particularly interesting since it is thought that our complex social interactions and the information processed in the social domain played an integral role in the development of primate’s mental capacities (Whiten and Byrne, 1988). If these pathways are active during REM sleep and this type of information is being rehearsed, then it should function to effectively strengthen the effects that processing of social information has on mental development. Further supporting this role is the tendency for a large proportion of dreams to contain other people and represent various social situations (Kahn et al., 2002).
Another example of a skill that has arguably played a pivotal role in other functional aspects of the human intellect and could serve to be shaped by dreaming is that of interpretation. As discussed by Bogdan (1997, p.108), “…key advances in interpretation, such as the recognition of belief, were accelerated by increased opportunities to interact with or manipulate subjects and slowed down by a lack of such opportunities.” As such, via teasing, play, mental rehearsal/imagery, or dreaming, the individual is given the opportunity to utilize successful strategies in dealing with these situations and further develop interpretive skills. In fact, studies of children’s dream-reports indicate that their dreams more often contain family members and close friends than adults’ dreams (Hobson, 1988), possibly due to the fact that it is more important for younger children to be practicing close interpersonal skills than it is for adults.
It, however, could be argued that the rehearsal of social situations would not play a significant role in increasing one’s fitness. In order to address this claim, it is necessary to comment on the potential benefits of being socially sophisticated. First, in terms of pure survival value, those individuals who best interact with those around them, i.e., those who interact without interpersonal conflict and confrontation, will likely have better access to resources in their social group, be it mates or food (Foley, 1989). There is wide variation between cultures in the types of traits that render an individual fit, and what makes humans a successful species is that our ability to deal with the social environment that we are thrust into is not completely pre-wired (Sapir, 1921; Whorf, 1956). Those individuals that could use feedback from the environment to effectively modify their social interactions would be best off, as individual groups often have particular social nuances. Also, clearly in our own species, the traits we have which help us deal with social situations vary greatly and under certain circumstances can be beneficial, while at other times potentially put us at risk. Due to the variable fitness of particular behaviors at particular times, we need to be adept at interpreting cultural standards when interacting with others. For example, one cultures “alpha male” could potentially be ostracized in another culture. This newly ostracized individual would be less likely to obtain mates, and would be less competitive for the resources that would influence his survival. Therefore, something that could tip the scale in allowing someone to best deal with important social interactions would likely be selected for over time.
Flanagan (2000) raises the potential criticism that dreams do not give us an accurate representation of ourselves and conspecifics, positing that there is no advantage conferred in dreams by rehearsing various social interactions. He claims that the development of a TOM module based on dreamed social interactions would be flawed, and that accurate depictions of others and ourselves is the exception rather than the rule while dreaming. While we do not disagree that in dreams ourselves and others often act in a surprising and atypical manner, overall our representation of those we know is quite impressive and accurate. From their visual appearance, to the tone of voice, to the style of speaking, by virtue of the fact that we recognize and interact with those we know in the dream-world, we have an amazing ability to unconsciously recreate dream characters from those people with which we typically interact (above and beyond any verbal description that we could give of that person). While we surely cannot say a dream character’s behavior is how that person would act in ‘real life,’ we also know that there is no way to accurately predict how that person will behave when encountering a new situation in real life. In waking life, the best that we can do is interpret overt cues and then attempt to understand a person’s intentions and predict their actions, for which dreams offer such a venue.
Situated Cognition in Dreams
Situated Cognition in Dreams
While the above argument points towards the similarity between thoughts while dreaming and in waking life, clearly there is a difference in how the two states are experienced and the type of cognition occurring in each. As discussed earlier, for the majority of time spent dreaming, we accept as real even the most bizarre scenarios, and are able to make rationalizations allowing us to treat the dream as real. Generally speaking, we are fooled into accepting a dream experience as a real experience, until we awake and reflect on the content of the dream. This indicates a general deficit in certain aspects of executive functioning (e.g., deficits in planning, monitoring, attention switching, etc.), including skills relating to critical-thinking and our ability to access specific types of memories.
While dreaming, an effect of the general deficit in executive functioning is that our cognitive machinery becomes fully engrossed in perceptions and goal-states directly relevant to perceptions of the dream. This has a considerable resemblance to the idea of situated cognition, in which cognition is tied to the moment and restricted to satisfying goals pertaining to current concerns (also, perceptual narrowing has been shown in alternate contexts within the rubric of the threat-rigidity effect, proposed by Staw, Sandelands, and Dutton, 1981). It can be argued that all non-human cognition is situated, and that it is the ability to extend thinking beyond the here-and-now of perception and motivation that makes human cognition unique (Bogdan, 1997). It has even been hypothesized that what humans currently experience during REM sleep shares a similarity to waking consciousness in early hominid brain evolution (Panksepp, 1998). Jaynes (1976) takes this idea even further by arguing that there was a time, roughly 3000 years ago, when humans lacked consciousness and acted in a way that parallels the situated nature of dream consciousness.
This situated aspect of dreaming also makes sense from an evolutionary perspective and further supports aspects of the threat-simulation theory. While it is advantageous to rehearse situations that are subjectively deemed as threatening, it is equally disadvantageous to come across a threatening scenario in real life and invest the time required to wonder whether or not that situation is real. Therefore, in order for this dream mechanism to be selected for, an important aspect of its initial selection is that the perceived threats encountered during a dream must be experienced as a real. This means that certain higher-order mental processes, which would function to appraise the situation in an intellectual fashion (mostly frontal areas), would likely have to be deactivated, which research indicates is the case (Mazur, Pace-Schott, Hobson, 2002).
In most dreams there are deficits in the ability to solve complex problems. Evidence from fMRI studies during REM sleep, show that there is a decrease in activity of the prefrontal cortex, which would normally be associated with a decrease in executive functioning (Mazur et al., 2002). Specifically, it has been found that there is a decrease in activity of the dorsolateral prefrontal cortex during REM sleep. This cortical region of the brain is crucial for tasks that require us to switch from our current line of thinking and inhibit a task once initiated. The deactivation of this region during a dream-state makes intuitive sense, in that for most dreams even very bizarre scenarios are normally accepted without question and we generally just go with the flow of the dream. We can visit with people who have passed away or interact with those whom we have not seen in years and yet this normally does not stop the dream from continuing or cause us to come to the conclusion that we are dreaming.
While the above argument points towards the similarity between thoughts while dreaming and in waking life, clearly there is a difference in how the two states are experienced and the type of cognition occurring in each. As discussed earlier, for the majority of time spent dreaming, we accept as real even the most bizarre scenarios, and are able to make rationalizations allowing us to treat the dream as real. Generally speaking, we are fooled into accepting a dream experience as a real experience, until we awake and reflect on the content of the dream. This indicates a general deficit in certain aspects of executive functioning (e.g., deficits in planning, monitoring, attention switching, etc.), including skills relating to critical-thinking and our ability to access specific types of memories.
While dreaming, an effect of the general deficit in executive functioning is that our cognitive machinery becomes fully engrossed in perceptions and goal-states directly relevant to perceptions of the dream. This has a considerable resemblance to the idea of situated cognition, in which cognition is tied to the moment and restricted to satisfying goals pertaining to current concerns (also, perceptual narrowing has been shown in alternate contexts within the rubric of the threat-rigidity effect, proposed by Staw, Sandelands, and Dutton, 1981). It can be argued that all non-human cognition is situated, and that it is the ability to extend thinking beyond the here-and-now of perception and motivation that makes human cognition unique (Bogdan, 1997). It has even been hypothesized that what humans currently experience during REM sleep shares a similarity to waking consciousness in early hominid brain evolution (Panksepp, 1998). Jaynes (1976) takes this idea even further by arguing that there was a time, roughly 3000 years ago, when humans lacked consciousness and acted in a way that parallels the situated nature of dream consciousness.
This situated aspect of dreaming also makes sense from an evolutionary perspective and further supports aspects of the threat-simulation theory. While it is advantageous to rehearse situations that are subjectively deemed as threatening, it is equally disadvantageous to come across a threatening scenario in real life and invest the time required to wonder whether or not that situation is real. Therefore, in order for this dream mechanism to be selected for, an important aspect of its initial selection is that the perceived threats encountered during a dream must be experienced as a real. This means that certain higher-order mental processes, which would function to appraise the situation in an intellectual fashion (mostly frontal areas), would likely have to be deactivated, which research indicates is the case (Mazur, Pace-Schott, Hobson, 2002).
In most dreams there are deficits in the ability to solve complex problems. Evidence from fMRI studies during REM sleep, show that there is a decrease in activity of the prefrontal cortex, which would normally be associated with a decrease in executive functioning (Mazur et al., 2002). Specifically, it has been found that there is a decrease in activity of the dorsolateral prefrontal cortex during REM sleep. This cortical region of the brain is crucial for tasks that require us to switch from our current line of thinking and inhibit a task once initiated. The deactivation of this region during a dream-state makes intuitive sense, in that for most dreams even very bizarre scenarios are normally accepted without question and we generally just go with the flow of the dream. We can visit with people who have passed away or interact with those whom we have not seen in years and yet this normally does not stop the dream from continuing or cause us to come to the conclusion that we are dreaming.
Beyond Threat Simulation
Beyond Threat Simulation
While Revonsuo (2000) limits his argument to the effectiveness of dreams in preparing for real-world threats, it is our goal now to extend this argument. We propose that the fitness-enhancing benefits of dreaming is not restricted to threat rehearsal, and the evolution of other higher-order cognitive faculties has been strongly influenced by a dreaming mechanism. By commenting on other fitness-enhancing aspects of the phenomenology of dreaming, besides threat, it also becomes possible to integrate our theory with portions of Hobson and McCarley’s (1977) activation-synthesis hypothesis, with particular regards to their view on the random information that leads to dreaming.
While dream content is not completely random, as demonstrated by the fact that there tends to be an over-representation of negative affect (Hall and Van de Castle, 1966; Merrit et al., 1994)) and social interactions (Kahn et al., 2002), there still is a great deal of variability and randomness observed in dream content. We argue that this variability is likely due to activation propagated from the brainstem, and that this noise in the system is beneficial. The advantages of having noise as a crucial factor in a dream-generation mechanism could be likened to the benefits of genotypic variability in the evolution of species (cf., Darwin, 1995). Given an unpredictable and variable environment, variability in traits increases the possibility that a certain trait will randomly confer an advantage under certain circumstances, this being the crux of Darwin’s theory of natural selection. In dreams, the potential advantage of noise and variability in the system allows for a broad range of scenarios to be simulated and new scenarios to be created rather than having the same type of dream occur repeatedly. This concept relates to ideas discussed by Kahn, Combs, and Krippner (2002), in terms of stochastic resonance which they contend prevents mental activity from perseverating, which allows for novel situations to be developed through the presence of noise in the system.
Aside from our theory being in a state of consonance with theories of both activation-synthesis and threat-simulation, we also contend that increased fitness is not limited to situations of threat rehearsal and that the information processing occurring in dreams should be similarly represented in the brain as is waking cognition. This is the case because if sleeping and waking cognition are quite different, then rehearsing threatening situations in a dream may not transfer into the ability to better handle similar situations in waking life. However, evidence from lucid dream studies (described below) indicate that tasks such as counting and singing during a dream, which should activate the left and right hemispheres, respectively, do just that. When a person is singing in a dream, their right hemisphere is more active, and conversely when a person counts, the left hemisphere becomes more activated (LaBerge and Dement, 1982). A more recent PET study demonstrated that subjects trained on a serial reaction time task showed task-related increases in brain activity during REM sleep which was correlated with improved performance on the task after sleep (Maquet et al., 2000).
Also, from a neuropsychological perspective, evidence comparing bizarre dream cognition with certain psychopathology indicates another link between brain activity in dreams and waking. For example, people who suffer from damage to frontal and temporal brain areas typically report the misidentification of faces during waking life, a condition known as Fregoli syndrome. Some research has indicated that a decrease of activity in these regions, reported from neuroimaging studies in sleep, correspond to similar reports of misidentification during dreaming (Schwartz and Maquet, 2002). So, the functional architecture of our brains similarly influences both sleep and waking cognition and perception, supporting the idea that
neurophysiological correlates of cognition appear stable across the two forms of consciousness.
While Revonsuo (2000) limits his argument to the effectiveness of dreams in preparing for real-world threats, it is our goal now to extend this argument. We propose that the fitness-enhancing benefits of dreaming is not restricted to threat rehearsal, and the evolution of other higher-order cognitive faculties has been strongly influenced by a dreaming mechanism. By commenting on other fitness-enhancing aspects of the phenomenology of dreaming, besides threat, it also becomes possible to integrate our theory with portions of Hobson and McCarley’s (1977) activation-synthesis hypothesis, with particular regards to their view on the random information that leads to dreaming.
While dream content is not completely random, as demonstrated by the fact that there tends to be an over-representation of negative affect (Hall and Van de Castle, 1966; Merrit et al., 1994)) and social interactions (Kahn et al., 2002), there still is a great deal of variability and randomness observed in dream content. We argue that this variability is likely due to activation propagated from the brainstem, and that this noise in the system is beneficial. The advantages of having noise as a crucial factor in a dream-generation mechanism could be likened to the benefits of genotypic variability in the evolution of species (cf., Darwin, 1995). Given an unpredictable and variable environment, variability in traits increases the possibility that a certain trait will randomly confer an advantage under certain circumstances, this being the crux of Darwin’s theory of natural selection. In dreams, the potential advantage of noise and variability in the system allows for a broad range of scenarios to be simulated and new scenarios to be created rather than having the same type of dream occur repeatedly. This concept relates to ideas discussed by Kahn, Combs, and Krippner (2002), in terms of stochastic resonance which they contend prevents mental activity from perseverating, which allows for novel situations to be developed through the presence of noise in the system.
Aside from our theory being in a state of consonance with theories of both activation-synthesis and threat-simulation, we also contend that increased fitness is not limited to situations of threat rehearsal and that the information processing occurring in dreams should be similarly represented in the brain as is waking cognition. This is the case because if sleeping and waking cognition are quite different, then rehearsing threatening situations in a dream may not transfer into the ability to better handle similar situations in waking life. However, evidence from lucid dream studies (described below) indicate that tasks such as counting and singing during a dream, which should activate the left and right hemispheres, respectively, do just that. When a person is singing in a dream, their right hemisphere is more active, and conversely when a person counts, the left hemisphere becomes more activated (LaBerge and Dement, 1982). A more recent PET study demonstrated that subjects trained on a serial reaction time task showed task-related increases in brain activity during REM sleep which was correlated with improved performance on the task after sleep (Maquet et al., 2000).
Also, from a neuropsychological perspective, evidence comparing bizarre dream cognition with certain psychopathology indicates another link between brain activity in dreams and waking. For example, people who suffer from damage to frontal and temporal brain areas typically report the misidentification of faces during waking life, a condition known as Fregoli syndrome. Some research has indicated that a decrease of activity in these regions, reported from neuroimaging studies in sleep, correspond to similar reports of misidentification during dreaming (Schwartz and Maquet, 2002). So, the functional architecture of our brains similarly influences both sleep and waking cognition and perception, supporting the idea that
neurophysiological correlates of cognition appear stable across the two forms of consciousness.
An Evolutionary Perspective
An Evolutionary Perspective
In order to evaluate the threat simulation theory of dreaming (of the kind found in REM sleep), it is useful to discuss it in an evolutionary context, and consider whether dreaming meets the necessary requirements of evolution by natural selection; namely, genetic variation, inheritance, and differential fitness. As for the first condition, there is evidence that REM sleep is genetically varied between and within species. REM sleep seems to be exclusive to placental and marsupial mammals (Winson, 1993). This suggests a particular phylogeny of dreaming, and that there was some point in time in which this characteristic was acquired and further spread to evolving species. Also, the amount of REM sleep placental and marsupial animals tend to require varies in a shared manner throughout their life cycle (Siegel, 1995), pointing towards an underlying genetic control over dreaming.
Likewise, different physiological processes occurring during REM must have
undergone processes of natural selection. Consider disorders in which people physically act out their dreams, and the potential dire consequences that could result from such disorders. Those who acted out their dreams may have put themselves at great risk. As the trait of physical inhibition during dreaming varies in humans, those individuals with the trait which inhibits paralysis during REM sleep seem to have been predominately removed from the current dreaming population, indicating also that the second condition of inheritance is satisfied.
When considering the third proposition of the differential fitness of dreaming in modern humans, it is important to understand the environment in which selection was occurring. Our human ancestors faced a number of challenges posed by interactions with conspecifics within and between groups (Foley, 1989), as well as in procuring food and protecting themselves from predators (Kaplan and Hill, 1985). In this environment, the ability to most efficiently react when a real threat is apparent would obviously confer a survival advantage. Evidence from mental imagery and dream studies suggest that rehearsal in the dream is treated as a real threat and, therefore, those individuals with these imagery skills to rehearse threatening scenarios should have an improved ability to deal with threat, making them more likely to be the progenitors of offspring. Through the survival and procreation of their offspring, this ability of, and propensity towards, imagery would be differentially passed on to future generations.
If dreaming was selected for because of its adaptive function, the general content of dreams should certainly reflect this, and consist of situations that allow the rehearsal of scenarios that ultimately lead toward increased fitness. This is exactly what is seen, with studies indicating that dream content is biased toward negative elements reflecting threat, as opposed to positive elements. Data collected from over 500 dream reports by Hall and Van de Castle (1966) indicate that about 80% contained negative emotions, while only about 20% contained positive emotions. These negative dreams are also disproportionably likely to contain threatening elements such as animals and male strangers in threatening encounters. The evidence points towards the overrepresentation of threatening events in dreams, which should not occur if dream content is random. Through appropriating and learning to deal with these threats in dreams, it is proposed here that an animal could increase its overall evolutionary fitness.
In order to evaluate the threat simulation theory of dreaming (of the kind found in REM sleep), it is useful to discuss it in an evolutionary context, and consider whether dreaming meets the necessary requirements of evolution by natural selection; namely, genetic variation, inheritance, and differential fitness. As for the first condition, there is evidence that REM sleep is genetically varied between and within species. REM sleep seems to be exclusive to placental and marsupial mammals (Winson, 1993). This suggests a particular phylogeny of dreaming, and that there was some point in time in which this characteristic was acquired and further spread to evolving species. Also, the amount of REM sleep placental and marsupial animals tend to require varies in a shared manner throughout their life cycle (Siegel, 1995), pointing towards an underlying genetic control over dreaming.
Likewise, different physiological processes occurring during REM must have
undergone processes of natural selection. Consider disorders in which people physically act out their dreams, and the potential dire consequences that could result from such disorders. Those who acted out their dreams may have put themselves at great risk. As the trait of physical inhibition during dreaming varies in humans, those individuals with the trait which inhibits paralysis during REM sleep seem to have been predominately removed from the current dreaming population, indicating also that the second condition of inheritance is satisfied.
When considering the third proposition of the differential fitness of dreaming in modern humans, it is important to understand the environment in which selection was occurring. Our human ancestors faced a number of challenges posed by interactions with conspecifics within and between groups (Foley, 1989), as well as in procuring food and protecting themselves from predators (Kaplan and Hill, 1985). In this environment, the ability to most efficiently react when a real threat is apparent would obviously confer a survival advantage. Evidence from mental imagery and dream studies suggest that rehearsal in the dream is treated as a real threat and, therefore, those individuals with these imagery skills to rehearse threatening scenarios should have an improved ability to deal with threat, making them more likely to be the progenitors of offspring. Through the survival and procreation of their offspring, this ability of, and propensity towards, imagery would be differentially passed on to future generations.
If dreaming was selected for because of its adaptive function, the general content of dreams should certainly reflect this, and consist of situations that allow the rehearsal of scenarios that ultimately lead toward increased fitness. This is exactly what is seen, with studies indicating that dream content is biased toward negative elements reflecting threat, as opposed to positive elements. Data collected from over 500 dream reports by Hall and Van de Castle (1966) indicate that about 80% contained negative emotions, while only about 20% contained positive emotions. These negative dreams are also disproportionably likely to contain threatening elements such as animals and male strangers in threatening encounters. The evidence points towards the overrepresentation of threatening events in dreams, which should not occur if dream content is random. Through appropriating and learning to deal with these threats in dreams, it is proposed here that an animal could increase its overall evolutionary fitness.
Threat Rehearsal
Threat Rehearsal
When awoken abruptly from a terrifying nightmare, it is easy to understand the strength dream imagery has in generating both physiological and cognitive responses. In the case of a nightmare, heart rate is accelerated, sweating occurs, and a general feeling of fear and anxiety can extend for some time after the dream has finished (Mellman et al., 1985). Even though dreams are a form of mental representation, in the sense that perception is not tied to stimuli in the environment, they are generally experienced as real and the content is perceptually indistinguishable from waking perception (Freud, 1900).
If merely imagining an event has the power to better prepare us for an actual event by physically activating comparable brain regions, then it should follow that the more realistic the simulation of events, the more the brain treats the information as real. Also, if this capacity to simulate an environment allows us to be optimally prepared to deal with challenges in a real environment, it should affect fitness and be naturally selected for across generations (Darwin, 1995). The threat-simulation hypothesis of dreaming argues that this is the purpose of dreams and the reason why dreaming has evolved (Revonsuo, 2000). It is suggested by this theory that dreams serve the purpose of allowing for the rehearsal of threatening scenarios in order to better prepare an individual for real-life threats. This is supported by evidence from dream reports to be discussed below.
When awoken abruptly from a terrifying nightmare, it is easy to understand the strength dream imagery has in generating both physiological and cognitive responses. In the case of a nightmare, heart rate is accelerated, sweating occurs, and a general feeling of fear and anxiety can extend for some time after the dream has finished (Mellman et al., 1985). Even though dreams are a form of mental representation, in the sense that perception is not tied to stimuli in the environment, they are generally experienced as real and the content is perceptually indistinguishable from waking perception (Freud, 1900).
If merely imagining an event has the power to better prepare us for an actual event by physically activating comparable brain regions, then it should follow that the more realistic the simulation of events, the more the brain treats the information as real. Also, if this capacity to simulate an environment allows us to be optimally prepared to deal with challenges in a real environment, it should affect fitness and be naturally selected for across generations (Darwin, 1995). The threat-simulation hypothesis of dreaming argues that this is the purpose of dreams and the reason why dreaming has evolved (Revonsuo, 2000). It is suggested by this theory that dreams serve the purpose of allowing for the rehearsal of threatening scenarios in order to better prepare an individual for real-life threats. This is supported by evidence from dream reports to be discussed below.
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