A New Neurocognitive Theory of Dreams
G. William Domhoff
University of California, Santa Cruz
NOTE: If you use this paper in research, please use the following citation, as this on-line version is simply a reprint of the original article:
Domhoff, G. W. (2001). A new neurocognitive theory of dreams. Dreaming, 11, 13-33.
Discoveries in three distinct areas of dream research make it possible to suggest the outlines of a new neurocognitive theory of dreaming. The first relevant findings come from assessments of patients with brain injuries, which show that lesions in different areas have differential effects on dreaming and thereby imply the contours of the neural network necessary for dreaming. The second set of results comes from work with children ages 3-15 in the sleep laboratory, which reveals that only 20-30% of REM period awakenings lead to dream reports up to age 9 and that the dreams of children under age 5 are bland and static in content. The third set of findings comes from a rigorous system of content analysis, which demonstrates the repetitive nature of much dream content and that dream content in general is continuous with waking conceptions and emotional preoccupations. Based on these findings, dreaming is best understood as a developmental cognitive achievement that depends upon the maturation and maintenance of a specific network of forebrain structures. The output of this neural network for dreaming is guided by a "continuity principle" linked to current personal concerns on the one hand and a "repetition principle" rooted in past emotional preoccupations on the other.
This paper builds on systematic evidence in three independent areas of dream research to suggest a new neurocognitive theory of dreams. These three bodies of scientific findings have come to maturity and a possible integration at an ideal moment because advances in neuroscience and computer software make it possible to test the new theory. It also may be a propitious moment for consideration of a new theory because the evidence from systematic studies does not fit well with the best-known clinical and neuropsychological theories (Domhoff, 1999; Domhoff, 2000b; Fisher & Greenberg, 1996; Foulkes, 1996a; Foulkes, 1999)
The new theory starts with findings from neuropsychological assessments of patients suffering brain injuries which reveal the areas of the brain that are and are not necessary for dreaming to occur (Solms, 1997; Solms, 2000); these discoveries are supported by neuroimaging and sleep laboratory studies (Braun et al., 1997; Braun et al., 1998; Heiss, Pawlik, Herholz, Wagner, & Wienhard, 1985; Kerr & Foulkes, 1981; Kerr, Foulkes, & Jurkovic, 1978; Maquet et al., 1996). Next, the theory adds findings on children who were observed over many hundreds of nights in the sleep laboratory to understand the developmental nature of dreaming (Foulkes, 1982; Foulkes, 1999; Foulkes, Hollifield, Sullivan, Bradley, & Terry, 1990). Then it incorporates the insights drawn from quantitative investigations of tens of thousands of dreams using a rigorous system of content analysis (Domhoff, 1996; Hall, 1969; Hall & Van de Castle, 1966).
Based on the results from these three empirical areas of dream research, it is possible to make the following generalizations that lead to a neurocognitive theory of dreams and many testable hypotheses:
- Dreaming depends on the normal functioning of a relatively specific neural network located primarily in the limbic, paralimbic, and associational areas of the forebrain. If there are defects in this network, dreaming can be lost temporarily or permanently, or be impaired in some way, such as loss of visual dream imagery:
- Dreaming is a cognitive achievement that develops gradually over the first 8 or 9 years of life.
- The "output" of the neural network for dream generation, called "dream content," and available to scientists through written or transcribed "dream reports," is generally continuous with waking conceptions and contains a great deal of previously unrealized repetition in characters, social interactions, misfortunes, negative emotions, and themes.
These generalizations lead to several hypotheses concerning the links between the neuropsychological, developmental, and content analysis findings:
- The fact that specific neural defects can lead to the loss or impairment of dreaming, when considered in conjunction with the fact that dreaming develops gradually in children, suggests that adult-like dreaming depends on the maturation of the neural network for dreaming. For example, the complete loss of dreaming in adults due to injuries to either inferior parietal lobe, when placed alongside the finding that increased dream reporting in young children correlates with visuospatial skills, suggests that the ability to dream in children depends in part upon the development of the neural network for spatial construction centered in the parietal lobes.
- The importance of limbic structures in dreaming, in conjunction with the repetitive nature of dream content, suggests that the "emotional brain" mapped out by LeDoux (1996) may be the basis for the repetitive nature of much dream content, including the nightmarish dreams accompanying post-traumatic stress disorder and temporal lobe epileptic seizures.
- The fact that dreams can be made more vivid and frightening by drugs affecting the dopaminergic system suggests that the relationship between the neural network for dreaming and dream content can be studied through determining the influence of various drugs on specific aspects of dream content.
- The fact that defects in the neural network for dreaming can lead to changes in dream content suggests that the general relationship between this network and specific aspects of dream content can be studied by examining the dream reports of patients in a wide variety of disease states.
- The many established parallels between waking cognition and dreaming raise the possibility that some dreams may make use of the vast system of figurative thinking shown by cognitive scientists to be pervasive in waking thought (Fauconnier, 1997; Gibbs, 1994; Lakoff, 1987).
Although the new theory sees dreams as psychologically meaningful in that they are coherent, relate to other psychological variables, and are continuous with waking conceptions and concerns, it does not claim any purpose or function for dreams. Based on current evidence, it is most likely that dreams are the accidental by-product of two great evolutionary adaptations, sleep and consciousness (Flanagan, 2000; Foulkes, 1993; Foulkes, 1999). However, their frequent dramatization of emotional preoccupations and their parallels with the figurative dimensions of waking thought may explain why many societies have invented cultural uses for dreams, usually in conjunction with religious ceremonies and medicinal practices.
The main findings on which the new theory is based are presented in the next four sections, along with several examples of how the three different types of findings can be related to each other. Although it is somewhat unusual to repeat published findings in a theoretically oriented paper, it is essential in this case because some of them are very little known. Moreover, it is also necessary to discuss the methodology upon which the developmental findings are based because parts of it have been inadequately characterized in some sources.
The Neural Network for Dreaming
Intrigued by reports of changes in dreaming or the complete loss of dreaming by some of the patients he examined as part of his clinical work, neuropsychologist Mark Solms (1997) questioned 361 consecutive patients in detail about possible changes in the frequency and nature of their dreaming. Twenty-nine patients turned out to be free of any brain lesions. They were used as a control group because they had been faced with the possibility of brain injuries, admitted to the hospital, and subjected to the same routines and tests as the patients who did suffer lesions.
Solms correlated the responses from the remaining patients concerning changes in their dreaming with the findings from their neurological tests and brain scans. He then turned his attention primarily to those patients with focal brain lesions so that causal inferences about specific regions of the brain could be made. These analyses led to the conclusion that there are two types of dreaming "deficits:" loss of visual dreaming and complete loss ("cessation") of dreaming. There are also two types of dreaming "excesses": increased frequency of dreaming and increased nightmare frequency. It is noteworthy that all four types of changes in dreaming correlate with waking cognitive defects. In addition, they relate to five relatively specific brain sites. Solms then integrated his findings with those from 73 published studies mentioning deficits and excesses in dreaming that are scattered throughout a neurological literature that goes back over 100 years. The result is a new neuropsychological theory describing the network of brain structures that provides the basis for dreaming (Solms, 1997; 2000).
Solms first found that 200 of the 332 patients with brain lesions reported no changes in dreaming, which is highly useful information in and of itself because it reveals those parts of the brain that are not necessary for dreaming: namely, the dorsolateral prefrontal cortex, the sensorimotor cortex, and the primary visual cortex. This finding is supported by PET scan studies of REM sleep (Braun et al., 1998; Heiss et al., 1985; Maquet et al., 1996).
Turning to the 132 patients who reported changes in their dreaming, Solms (1997) found 112 patients with forebrain lesions who lost dreaming for varying periods of time or permanently. Since none of these patients had brainstem injuries that might interfere with the triggering of Rapid Eye Movement (REM) sleep, these findings show that REM sleep is not sufficient for dreaming. Looking only at the non-dreaming patients with localized lesions, the loss of dreaming appears to be due to two different types of forebrain lesions. First, 47 of these patients had focal lesions in one or both of the parietal lobes. For many of these patients, dreaming returned when the lesions healed. They also showed a decline in waking visuospatial abilities while dreaming was absent. This finding led Solms (1997) to the hypothesis that the cortical network for spatial representation, located primarily in the parietal lobes (Robertson, 1998), is essential for dreaming.
Nine other cases of complete loss of dreaming had bifrontal focal lesions in the white matter inferior to the frontal horns of the lateral ventricles. This area provides a crucial link between limbic structures and frontal cortex. While the evidence for the importance of this area may seem weak because it is based on a small number of cases, Solms strengthens his argument by drawing on the previously overlooked literature reporting the complete loss of dreaming in 70-90% of the hundreds of schizophrenic patients who were leucotomized between 1940 and 1975 as a way to control their symptoms (Frank, 1946; 1950; Solms, 1997; 2000). In some of the more recent cases, this absence of dreaming was confirmed with awakenings in the laboratory during REM (Jus et al., 1973). Once again highlighting the parallels between waking cognition and dreaming, most of these patients were lacking in initiative, curiosity, and fantasy in waking life.
Third, Solms had 10 cases where focal injuries in the frontal-limbic region led to reports of excessive and very vivid dreaming of a highly realistic nature. These patients complained of dreamlike thought in waking life. Observations by hospital staff and the patients' own testimony also suggested that they were suffering from a confusion of dreaming and waking thought. Fourth, Solms had 9 patients with lesions in the temporal lobe who suffered from greatly increased nightmares of a repetitive nature.
Finally, Solms had two patients with injuries to the visual association cortex. One lost all visual imagery in dreams for a short time, the other was able to see static dream images from time to time. Both had one or another difficulty in terms of waking mental imagery. These findings correspond with 13 cases that go back to the 1880s in the neurological literature. They also parallel findings in laboratory studies by Foulkes and his colleagues. The case with no visual imagery in dreams is similar to Kerr, Foulkes, and Jurkovic's (1978) sleep laboratory study of a patient with damage in her visual association cortex who had neither waking mental imagery nor any visual imagery in her dreams. Solms' case with static dream imagery is described by him (1997, p. 105) as "strikingly reminiscent" of a second patient studied in the laboratory by Kerr and Foulkes (1981).
Solms puts the five lesion sites together as follows to provide the foundation for a neurocognitive theory of dreaming. First, he hypothesizes that the initiating mechanisms of the neural network for dream generation are probably located in the temporal-limbic region because of the increased nightmare frequency in patients with temporal lobe seizures. He argues that this area provides "affective arousal" (Solms, 1997, p. 243). Second, he sees the bifrontal white matter as a vital linkage between frontal cortex and the dopaminergic circuits that provide the "appetitive interest" necessary for dreaming. This hypothesis is based in good part on the loss of initiative, curiosity, and exploratory interest in the schizophrenics who were leucotomized, but a similar waking syndrome was noticed in several of his bifrontal cases as well. Third, he believes that the frontal-limbic area is a necessary component of the dream generation system because it provides an element of "selectivity" to the dream's content.
However, these three brain areas are not enough in and of themselves for dreaming to occur because the parietal lobes must be able to provide the critical element of spatial representation. Solms (1997, p. 271) reports there is even some evidence that the left parietal region "contributes symbolic (quasispatial) mechanisms to the dream process whereas the right parietal region contributes concrete spatial mechanisms," but he also stresses that this claim needs further investigation. Finally, the visual association cortex located in the occipito-temporal area is necessary for the dream to have a visual aspect. PET scan studies of REM sleep support many parts of Solms' overall viewpoint. They too show that limbic, paralimbic, inferior parietal, and occipito-temporal areas are active at this time (Braun et al., 1997; Braun et al., 1998; Heiss et al., 1985; Maquet et al., 1996).
As should be apparent, this theory does not give any direct role to the brainstem or REM sleep in generating dreams. Just as the cessation of dreaming due to parietal lobe or deep bifrontal lesions shows that REM is not sufficient for dreaming, the fact that temporal lobes seizures can cause dreaming in non-REM (NREM) sleep adds to the evidence from NREM awakenings in sleep laboratory studies suggesting that brainstem stimulation and REM are not necessary for dreaming (Antrobus, 1991; Domhoff & Schneider, 1999; Foulkes, 1962; Foulkes & Schmidt, 1983; Foulkes & Vogel, 1965; Herman, Ellman, & Roffwarg, 1978). However, the new theory is consistent with the fact that dreaming most often occurs during REM because the temporal-limbic region that is the trigger site for dreaming is regularly stimulated by the periodic activation of the brainstem (Hobson, Pace-Schott, & Stickgold, 2000).
There are major disagreements between Solms and the brainstem dream theorists about the role of brainstem mechanisms in triggering the dream state (Hobson & McCarley, 1977; Hobson et al., 2000; Hobson, Stickgold, & Pace-Schott, 1998). The brainstem theorists now claim that brainstem mechanisms are essential for dreaming even in late-night Stage II NREM dreams. They have altered their original theory, which claimed that dreaming only occurred during REM, to acknowledge some dreaming during Stage II NREM late in the sleep period, but they continue to insist that the brainstem is the only source of the "in-puts" that lead to dreams (Hobson, 1992; Hobson et al., 2000). It is for this reason that they are now best understood as "brainstem" theorists rather than "REM" theorists.
Despite these disagreements about the role of the brainstem, there is nonetheless broad agreement that a forebrain network along the lines suggested by Solms is necessary for dreaming. There is also agreement that this network plays the major role in terms of shaping dream content (Hobson et al., 2000; Hobson et al., 1998). For those who want to develop a neurocognitive theory of dreams that encompasses the whole range of dream content, it is now the forebrain network for dream generation that is the real issue, especially when it is recalled that there is no evidence that "phasic" events during REM have any influence on dream content (Foulkes, 1996a; Pivik, 1978; Pivik, 1986).
This forebrain network also seems to be a good starting point for understanding the occasional occurrence of an awareness of dreaming during a dream, a phenomenon that enjoyed a flurry of attention and speculation in the 1980s under the morally toned label of "lucid dreaming," implying a superior or elite status for "lucid dreamers" (Gackenbach & Bosveld, 1989; LaBerge, 1985; LaBerge, Nagel, Dement, & Zarcone, 1981). If dreaming is the form that consciousness takes during sleep (Foulkes, 1999), and if changes in the neural network for dreaming underlie different dreaming states, then "lucid" dreaming may be a product of a dream state in which the higher-order neural patterns that give us "core consciousness" and an "autobiographical self" are more active than usual (Damasio, 1999). This speculation is consistent with the finding that higher levels of alpha activity during REM are related to lucid dream reports (Tyson, Ogilvie, & Hunt, 1984), as is the fact that self-awareness during REM is associated with phasic activation within the REM period (Bradley, Hollifield, & Foulkes, 1992). So is a finding on the more "realistic" nature of the content of lucid dreams (Gackenbach, 1988).
Then, too, it is noteworthy that dream reports in an exploratory PET scan study of l2 male participants showed a greater sense of control when the medial frontal cortex and rectal orbital gyrus were more active, and a greater sense of things being out of control when the amygdala was most active (Shapiro et al., 1995). There is also non-laboratory evidence suggesting that a "lighter" stage of sleep closer to waking fantasy life may be the primary explanation for this phenomenon: most lucid dreams happen late in the sleep period when sleep consists of REM and Stage II of NREM. In fact, lucid dreams seem to happen most often after an early morning awakening that is followed by imagery rehearsal and a conscious attempt to be aware of dreaming upon falling back to sleep (LaBerge, 1985). Whether these people are in REM or Stage II NREM, the new question of interest due to Solms' findings is the overall state of a forebrain neuropsychological network that is able to generate dreams in either of those two stages of sleep.
In addition to examining the relationships among dream content, awareness during dreaming, and the forebrain network, there is still much to be learned about how the network itself actually operates, and there are issues to be clarified about two of Solms' (1997) explanatory concepts. There is a need for cautious consideration of his Freudian-derived speculation that some areas in the frontal lobes may play an inhibitory role that turns impulses away from the prefrontal cortex and sends them "backwards" to the inferior parietal lobes and the visual association cortex. Also, his claim that the neural network for dreaming may "protect" sleep in a fashion hypothesized by Freud would need to be demonstrated in great detail given (1) the adequacy of sleep in preschool children before they develop dreaming (Foulkes, 1982; Foulkes, 1999) and (2) the ability of leucotomized schizophrenics who do not dream to show normal sleep, including sleeping throughout REM periods, in the sleep laboratory (Jus et al., 1973). Moreover, it seems likely that mechanisms for maintaining sleep in the face of brainstem activation or other internal stimulation developed along with REM sleep in early mammals, long before there is any likelihood that dreaming was a part of sleep (Foulkes, 1983).
What seems certain is that progress toward an increasingly detailed mapping of this network is inevitable in an era in which neuropsychology is making rapid strides and neuroimaging studies are becoming increasingly sophisticated and commonplace. The stage is therefore set for a consideration of how this network might relate to the cognitive development of dreaming.
The Development of Dreaming Cognition
The serendipitous discovery of sleep stages in 1953, especially the finding that the four or five REM periods of the night lead to dream reports from 80-90% of awakenings in most normal teenagers and adults, triggered an enormous advance in the understanding of both sleep and dreaming (Dement & Kleitman, 1957a; 1957b; Foulkes, 1966; Kamiya, 1961). These studies demonstrated that dreaming is far more ubiquitous in both REM and NREM than any previous dream theorist ever imagined, that it cannot be triggered by external stimuli, and that dream content is by and large impervious to the wide range of presleep and concurrent stimuli that have been used in an attempt to influence it (Foulkes, 1985; 1996a). They further show that dreams collected from awakenings in the sleep laboratory, whether from REM or NREM, are in large measure coherent and reasonable simulations of the real world, which suggests there is a greater parallel between dreams and waking thought than is assumed by either clinical or brainstem dream theorists (Cavallero & Foulkes, 1993; Foulkes, 1985; Meier, 1993; Snyder, 1970; Strauch & Meier, 1996).
It is within the context of this general evidence for the overlap of waking cognition and dreaming that two-large scale studies of dreaming in children, one longitudinal, one cross-sectional, provide systematic evidence that can provide a developmental dimension to a neurocognitive theory of dreams (Foulkes, 1982; Foulkes, 1999; Foulkes et al., 1990). The longitudinal study began with 7 boys and 7 girls ages 3-4 to cover the ages 3-9 over the five-year span of the study. It also included 8 girls and 8 boys ages 9-10 to account for the years between 9 and 15. Remarkably, all of the 14 children in the younger group participated in all five years of the study. Twelve of the 16 in the older group completed the study; the other 4 moved out of town.
To check on the possibility that participation in the study improved dream recall and accounted for any increases in the frequency and narrative complexity of dream reports, 6 boys ages 11-13 were added to the older group in the third year and 7 girls ages 7-9 were added to the younger group in the fifth year. The new participants generally did not differ on any dream measures from the original participants. In total, 26 children between the ages of 3 and 15 participated for five full years, 34 for at least three years, and 43 for at least one complete year. Normative dream data for each group were collected during the first, third, and fifth years of the study, when children slept in the laboratory for 9 nights each. They responded to 3 awakenings a night from either REM or NREM for a total of 2,711 awakenings. All the awakenings were carried out by Foulkes to insure experimenter consistency. During the second and fourth years the children participated in a variety of methodological studies, the most important of which compared dreams collected after a night of uninterrupted sleep in the laboratory with dreams collected in the morning at home by parents.
In addition to information on the frequency of dream recall and the content of the dream reports, a wide range of personality and cognitive tests were administered by other members of the project team. Information about school performance was obtained. Observations of the youngest group were made at a two-week nursery school during the first three summers of the study. Six hundred fifty-seven non-dream variables were correlated with the dream data because "it would have constituted criminal neglect to have collected so many dream data and not to have searched far and wide for waking variables related to them" (Foulkes, 1999, p. 49).
The cross-sectional study focused on children ages 5-8 to see if the most interesting results of the longitudinal study could be replicated. It included 20 children at each age who were within one month of their birthday, so 80 children spent 3 nights in the sleep laboratory. They were each awakened 10 times, with all of the 800 awakenings once again carried out by Foulkes. The children also took several cognitive tests measuring visuospatial, verbal, descriptive, and memory abilities that had correlated with dream recall or length of dream reports in the first study. In neither study did Foulkes know the results of the daytime tests until he had collected all of the dream data.
There are several replicated results from these two studies that are important for a neurocognitive theory of dreams. None of the findings on rate of recall, report length, or narrative complexity showed any gender differences. First, and most unexpected, the median rate of dream recall was only 20-30% from REM awakenings until ages 9-11, when the median recall rate of 79% from REM awakenings approached adult levels. Recall from NREM awakenings went from 6% at ages 5-7 to 39% at ages 11-13. For both REM and NREM awakenings, recall came first from awakenings late in the night, then from awakenings in the middle of the night, and finally from awakenings early in the sleep period.
Second, the children's dream reports had very different content until ages 13-15 than what is reported by adults. For children under age 5, the REM reports consisted primarily of static and bland images in which they saw an animal, or were thinking about eating or sleeping. The dreams of children ages 5-8 showed a sequence of events in which characters moved about and interacted, but the dream narratives were not very well developed. Compared to the dream reports of adults, those of the young children were notable for their low levels of aggressions, misfortunes, and negative emotions (Domhoff, 1996; Foulkes, 1982; 1999). Gender differences in dream content did begin to appear in late childhood (Domhoff, 1996; Foulkes, 1982), but were more prevalent by adolescence (Trupin, 1976).
The results on both recall and content are of great theoretical importance because they suggest that young children do not dream in the fashion expected by either the clinical or brainstem theorists. Instead, they reveal dreaming to be a cognitive achievement that develops gradually in the same way many other cognitive abilities develop in children. The frequency and cognitive structure of children's dreams is not adult-like until ages 9-11, and the dream reports are not adult-like in length or content until ages 11-13. Although Freud (1900) claimed that the dreams of preschool children--often overheard in the form of sleeptalking -- are excellent evidence for his theory that all dreams contain an attempt at wish fulfillment, Foulkes concluded there are no signs of wishes in their cognitively impoverished dream reports. Freudians can rightly argue that the possibility of latent wishes cannot be ruled out unless free associations are also collected and analyzed, but Foulkes' conclusion may be strengthened by the fact that micro-awakenings of from 10 to 20 seconds occur several times a night in both children and adults, raising the possibility that the overheard "dreams" that form the basis for the most famous pre-school cases are in fact instances of sleeptalking in brief waking states (Arkin, 1981; Boselli, Parrino, Smerieri, & Terzano, 1998; Mathur & Douglas, 1995).
For the brainstem theorists, the absence of dreaming from so many REM periods is clearly a major surprise because of their continuing effort to place most "real" dreaming within REM or "covert" REM sleep (Hobson et al., 2000; Nielsen, 2000). The fact of significant NREM reporting by ages 11-13, especially from Stage II NREM late in the sleep period, also contradicts their expectations. To deal with the low recall from REM periods, they could have modified their view to say that REM is necessary but not sufficient, but instead Resnick, Stickgold, Rittenhouse, and Hobson (1994) argue that the children in Foulkes' studies felt uncomfortable and inhibited in the laboratory. They then present their own evidence of full-fledged dreams from preschool children on the basis of home-reported dreams collected by parents, sometimes after having the children tell themselves at bedtime that they will remember a dream in the morning.
Contrary to their claims, Foulkes (1982; 1999) presents detailed evidence that his extensive efforts to make the children comfortable in the laboratory setting did prove successful. In addition, he tested for the possible effects of awakenings during the second and fourth years by allowing the children to sleep throughout the night in the laboratory and then report any dreams they recalled in the morning. This procedure showed there were no differences with dreams collected after morning awakenings at home, which means any differences found in other studies between dreams collected from awakenings in the laboratory and at home are due to selective recall for atypical dreams at home rather than to any alleged inhibitory effect in the laboratory (Foulkes, 1979; 1982; 1996b).
Foulkes (1996b; 1999) also notes that the implicit pressures to recall dreams in the Resnick, Stickgold, Rittenhouse, and Hobson (1994) study might have led to made-up dream reports on the part of the children. Since many pre-school children seem to have an understanding of what dreaming is (Woolley, 1995), despite the paucity of their own dream lives, there is now a need for new research on the way in which children's "theory of mind" interacts with what they learn about dreams from their parents and books to produce their beliefs --and reports-- about dreams.
Foulkes' findings on the waking correlates of dreaming and dream content in children provide further surprises because verbal and linguistic skills do not play a role until dreaming is fully developed, and none of the personality measures correlated with dream content until preadolescence. The one good and consistent predictor of the frequency of dream reporting in children ages 5-9 in both studies is visuospatial skills, as best measured by the Block Design test of the WISC. This leads to the hypothesis that visual imagination may develop gradually and be a necessary cognitive prerequisite for dreaming.
There has been no rush to draw out the implications of this finding. Instead, skeptics argue that the low rates of recall in young children may be due to the way in which they encode the dream experience rather than a lack of dreaming. For example, Hunt (1989) thinks the problem may be an inability to distinguish the "embedded" experience of a dream from other subjective states; others say that children simply may lack the linguistic skills to translate the non-verbal experience of dreaming into the narrative report necessary to show evidence of dreaming (Hobson et al., 2000; Weinstein, Schwartz, & Arkin, 1991). Foulkes finds these alternative explanations unlikely because none of the several linguistic, descriptive, memory, and story telling tests administered to the children correlated with rates of recall. Such explanations are also contradicted by the fact that both REM and NREM reports are first given late in the sleep period; it does not seem likely that either discriminatory or narrative skills would be unavailable earlier in the night once they had developed.
The idea that young children do not dream very well until their visuospatial skills are developed is supported by Foulkes' findings with two of the boys ages 11-13 ages who were added to the study during its third year. Both of them had average memory and verbal skills, and both were adequate students in school, but both turned out be very low on visuospatial skills. Neither reported very many dreams during REM awakenings, far below the average for all other children in their age group. Since neither of these boys lacked the linguistic skills claimed by critics to be the reason why younger children do not report dreams when awakened in the laboratory, it seems more likely that they were not dreaming when awakened during REM sleep.
Once children have the ability to dream, their linguistic and descriptive skills begin to correlate with the length and narrative complexity of their dream reports. Still, it is not until ages 11-13 that dream content shows any relationship to personality dimensions. For example, individualistic and assertive children portray themselves as more active in their dreams. Children with more violence in their waking fantasies have more aggressive interactions in their dreams, and those who display the most hostility before going to bed in the laboratory more often dream of themselves as angry. These findings on the continuity of dream content with waking mentation support findings in earlier studies of children in the laboratory (Foulkes, 1967; Foulkes, Larson, Swanson, & Rardin, 1969; Foulkes, Pivik, Steadman, Spear, & Symonds, 1967). They suggest that dreams can reflect personality dimensions once there is an adequate level of cognitive development. In effect, this finding is what remains of the large claims by clinical dream theorists (Domhoff, 1999).
Foulkes' overall findings raise the possibility that the development of dreaming may be based on the maturation of the forebrain network for dreaming discussed in the previous section. This hypothesis is suggested most strongly by the parallel between the dependence of dreaming in children on visuospatial skills, which are based primarily in the parietal lobes (Robertson, 1998), and the loss of dreaming in adults with injuries to either parietal lobe. It is also suggested by the static nature of preschool children's dreams and the absence of movement imagery in the dreams of adults with lesions in specific parts of the visual association cortex.
More generally, if the low levels of dreaming in children and the differences in their dream reports from normative adult findings are treated as if they were "deficits," then the search could be made for possible causal "defects" in the neuropsychological network necessary for dreaming. This strategy has been followed by Welsh, Pennington, and Groisser (1993) in studying the development of frontal lobe executive functions in children, employing neuropsychological tests in conjunction with standard developmental tests. It could be widened to include neuroimaging studies of the developing brain and myelination studies as well (Chugani, 1999; Paus, Zijdenbos, Worsely, Collins, & others, 1999; Rivkin, 2000; Thatcher, 1996). Indeed, the fact that myelination of the inferior parietal lobules is not functionally complete until ages 5-7 may be part of the reason why dreaming is not fully developed until after that age period (Solms, 1999).
The integration of the neural network for dreaming with the cognitive theory of dreaming developed by Foulkes (1985; 1999) would provide a solid basis for a theory that is genuinely "neurocognitive" instead of simply "neuropsychological," in the sense that it would have the potential to relate a general neural system to the general nature of dreaming. However, it also would be necessary to incorporate what is known about the nature of dream content, which is the topic of the next two sections.
The Nature of Dream Content
Although there are several systems of content analysis that have made one or more contributions to the overall understanding of dream content (Foulkes & Shepherd, 1971; Gottschalk & Gleser, 1969; Winget & Kramer, 1979), the largest and most systematic body of findings on what people dream about comes from a comprehensive set of categories developed by Calvin S. Hall (1951), and then finalized with the help of a co-worker (Hall & Van de Castle, 1966). It is also one of the few coding systems that has been used extensively by investigators other than those who created the system, including researchers from Japan, India, Switzerland, and the Netherlands, and it has proven useful with dreams collected by anthropologists in small traditional societies as well (Domhoff, 1996).
There are four general findings with the Hall/Van de Castle system that must be encompassed by a neurocognitive theory of dreams. First, several different studies reveal that the dream lives of college men and women in the United States remained the same throughout the second half of the 20th century despite major cultural changes (Domhoff, 1996; Dudley & Swank, 1990; Hall, Domhoff, Blick, & Weesner, 1982; Tonay, 1990/1991). Second, there is little or no change in dream content with age once adulthood is reached. That is, older dreamers do not differ from college students, except perhaps for a decline in physical aggressions and negative emotions (Cote, Lortie-Lussier, Roy, & DeKoninck, 1996; Hall & Domhoff, 1963; Hall & Domhoff, 1964; Howe & Blick, 1983; Lortie-Lussier, Cote, & Vachon, 2000; Strauch, 2000; Zepelin, 1980). Nor does dream content change much in longitudinal studies of dream journals provided by adults, a claim that holds true for periods as long as four or five decades and for people still keeping journals in their seventies (Domhoff, 1996; Hall & Nordby, 1972; Smith & Hall, 1964).
The third relevant result with the Hall/Van de Castle system is that there is a stable pattern of cross-cultural similarities and differences. Everywhere in the world, for example, women and men have the same differences in the ratio of male to female characters in their dream reports, with women dreaming equally of men and women, and men dreaming about other men by a 2:1 ratio (Hall, 1984). For both men and women, there is usually more aggression than friendliness, more misfortune than good fortune, and more negative emotions than positive emotions (Domhoff, 1996). In addition to these similarities, there are also a few differences that make sense in terms of large-scale cultural differences. Small traditional societies have a higher percentage of animal characters, and there are variations from society to society in the percentage of all aggressive interactions that are physical in nature, although it is also the case that men in almost all societies have a higher physical aggression percent than women (Domhoff, 1996; Gregor, 1981; O'Nell & O'Nell, 1977).
Fourth, studies of dream journals have demonstrated wide individual differences in high and low frequencies on a variety of Hall/Van de Castle indicators that are in general continuous with the waking conceptions and past or present emotional preoccupations of the dreamers. That is, contrary to Jung's (1974) emphasis on the compensatory nature of dreams, in which aspects of the personality neglected in waking life are highlighted in dreams, there is a continuity between dream content and waking thought (Bell & Hall, 1971; Domhoff, 1996; Hall & Lind, 1970; Hall & Nordby, 1972). This finding leads to the hypothesis of a "continuity principle" in dreams that is compatible with Foulkes' (1967; 1982; 1999) findings in laboratory studies with both children and adults. This hypothesis is best demonstrated by blind analyses of dream journals where nothing is known about the dreamer until she or he later answers questions developed on the basis of the content analysis (Domhoff, 1996).
Several of these discoveries with the Hall/Van de Castle system, and especially the consistency in what adults dream about throughout most of their lifetimes, lead to the idea that there is a "repetition principle" in dreams (Domhoff, 1993; Domhoff, 1996). This tendency to repeat has gone unnoticed by those who study one dream at a time with clinical patients, use samples of individual dream reports from groups of people, or hold to Jung's (1974) theory that a dream series shows a pattern of symbolic change toward greater personal integration. The idea of a repetition principle in dreams not only accounts for the consistency over years and decades in characters, social interactions, activities, and settings in longitudinal studies using the Hall/Van de Castle system, but it encompasses and makes sense of three other repetitive aspects of dream life that must be comprehended within a neurocognitive theory of dreaming.
First, there is a large clinical literature on the repetitive nightmares of people suffering from post-traumatic stress disorder that fits well with the idea of a repetition principle (Hartmann, 1984; Hartmann, 1998; Kramer, 2000; Kramer, Schoen, & Kinney, 1987). Second, the repetition principle can encompass the recurrent dreams that 50-80% of people claim to have had at one time or another in their lives, often starting in late childhood or early adolescence, sometimes lasting for the rest of their lives, and usually highly negative in content and emotionally upsetting (Cartwright & Romanek, 1978; Robbins & Houshi, 1983; Zadra, 1996). Third, the idea of a repetition principle can incorporate the repeated themes found in most series of 20 or more dreams (Hall, 1947; 1953c; Hall & Nordby, 1972; Jung, 1974; Mattoon, 1978). In other words, it is not just Hall/Van de Castle indicators that are consistent over many years, but also more general themes like being lost, preparing meals, or being late for an examination. In one journal consisting of 904 dreams over a 50 year period, for example, just six themes accounted for at least part of the content in 76% of the dream reports (Domhoff, 1993).
The repetition principle suggests several potential linkages between dream content and the neural network for dreaming, particularly in terms of its possible relationship with the vigilance/fear system that seems to be centered in the amygdala (Le Doux, 1996; Whalen, 1998). The best examples of this point, of course, are the repetitive nightmares of post-traumatic stress disorder, which sometimes happen in Stage II of NREM (Van der Kolk, Blitz, Burr, Sherry, & Hartmann, 1984) and seem to have parallels with the nightmares suffered by epileptics due to seizures in NREM (Solms, 1997; 2000). Then, too, studies using stereotaxic electrodes to locate the sites causing seizures in epileptic patients show that the "dreamy state" sometimes experienced as part of the diagnostic process is related to the temporal-limbic region. In one large-scale study, the amygdala, anterior hippocampus, and temporal neocortex were involved in every spontaneous occurrence of this state during the procedure (Bancaud, Brunet-Bourgin, Chauvel, & Halgren, 1994). Thus, future neuroimaging work on both post-traumatic stress disorder and epilepsy may hold promise for linkages between the repetition principle and the neural network for dreaming.
However, there need not be an exclusive focus on patients. The consistency of emotionally painful themes and of heightened scores on Hall/Van de Castle indicators in the dreams of many normal participants suggest that their dream life is often "stuck" in the past in a way that fits with the persistence of negative memories stored in the vigilance/fear system (Domhoff, 1996). Both dreams and the vigilance/fear system seem to provide a neurocognitive record of traumas, upsets, and tensions over a lifetime. Moreover, both may persist even when the person seems emotionally recovered and unhampered by the past during waking life.
Systematic studies showing the effects of different drugs on dream content, when done in conjunction with neuroimaging studies, might help to pinpoint relationships between repetitive dream content and specific components of the dream-generation network. The promise for such studies is seen in the fact that both alkaloids (Cartwright, 1966; Ketchum, Sidell, Crowell, Aghajanian, & Hayes, 1973) and dopamine (Hartmann, Russ, Oldfield, Falke, & Skoff, 1980; Solms, 1997; 2000) intensify the dream experience. Patients suffering from epilepsy or Parkinson's Disease might be potential candidates for such content studies because it already is known that the medications that eliminate epileptic seizures also reduce or eliminate the patients' nightmares, and that L-dopa potentiates the dream experience for Parkinson's patients (Bearden, 1994; Hartmann, 1984; Solms, 1997).
Although earlier content studies on the effect of drugs on dreams led to few clear results for a variety of reasons (Roth, Kramer, & Salis, 1979), the potential for pre/post studies of individual cases is shown in the large positive changes in the dream content of a 21-year-old woman after she began taking an SSRI to cope with anxiety attacks (Kirschner, 1999). These positive changes include more friendly interactions, fewer aggressive interactions, and fewer negative emotions. In terms of the repetition dimension as an indicator of fixation to the past, it is also of interest that she showed a decline in "elements from the past" as well.
Dream content and the neural network for dreaming also might be linked by investigations that correlate specific neurological defects with atypical scores on Hall/Van de Castle indicators, or that track the relationship between the return of dreaming after parietal lobe injuries and changes in dream content. The potential for such studies is demonstrated in older reports cited by Solms (1997) showing a decline in "narrative complexity" in the dream reports of patients with specific defects through injuries or operations. It is also seen in a study showing that 17 male chronic brain syndrome patients had more family members, less aggression, and less emotional content in the 31 dreams they reported than did the Hall/Van de Castle normative sample (Kramer, Roth, & Trinder, 1975). This pattern of findings suggests that their dreams were very bland, a characterization which fits with the waking personalities of such patients (Torda, 1969).
Patients who have suffered damage to the amygdala might be ideal candidates for future defect studies because they have lost their capacity for fear in waking life and express predominantly positive emotions (Adolphs & Damasio, 1998; Damasio, 1999). It therefore could be hypothesized on the basis of the continuity principle that their negative emotions percent would be far lower than the 80% figure that has been found in several different studies (Hall et al., 1982; Hall & Van de Castle, 1966; Merritt, Stickgold, Pace-Schott, Williams, & Hobson, 1994; Roussy, Raymond, & De Koninck, 2000; Tonay, 1990/1991). It might even be that there is a different profile on Hall/Van de Castle indicators for each type of defect (Domhoff, 2000a).
Dream Content and Waking Cognition
Findings from the study of dream content not only suggest links with the neural network for dreaming, but also with waking cognition. In particular, the continuity principle established through blind analyses of individual dream journals provides the same kind of strong connection between dreaming and waking cognition that has been demonstrated by other evidence presented earlier in this paper. This continuity leads to the hypothesis that both of these cognitive states are dealing with the same psychological issues to a large extent. It thereby provides the basis for a neurocognitive theory of dreams that starts with the idea that dreams express our conceptions of ourselves and others, an idea developed in earlier cognitive theories of dreams (Fiss, 1986; Foulkes, 1985; Hall, 1953b). The emphasis is on conceptions of "self" and "others" because studies of adult dream content show that dreams reflect relatively little about a person's attitudes toward current events and politics (Hall, 1951). Similarly, (Foulkes, 1982; 1999) found that children between ages 5 and 15 dreamed very little of their two most time-consuming daytime activities, going to school and watching television; instead, they dreamed about recreational activities.
An emphasis on the highly personal nature of dreams may explain why the dreams of college students in the United States have not changed over the past 50 years; the culture has changed, but personal concerns probably remain very stable. This emphasis also may explain why dreams are more similar than they are different around the world. As anthropologist Thomas Gregor (1981, p. 389) suggests at the conclusion of his detailed study of 385 dream reports from men and women in a very small native group deep in the Amazon jungle, "it may be possible to show that the dream experience is less variant than other aspects of culture."
However, as the evidence presented earlier concerning the importance of the repetition principle shows, the continuity principle does not operate entirely in terms of current personal interests and concerns. Dream content is also continuous in varying degrees for different individuals with past waking concerns. Discrepancies between current waking concerns and current dream content, such as dreaming about painful events that the person no longer thinks about in waking life, could be used to see how the continuity and repetition principles interact with each other to shape dream content.
Studies of dream content also might provide a link between waking cognition and dreaming to the degree it can be demonstrated that dreams use the same conceptual metaphors, metonymies, and conceptual blends that cognitive linguists and psycholinguists have shown to be pervasive in waking thought (Fauconnier, 1997; Gibbs, 1994; Gibbs, 1999; Lakoff & Johnson, 1980; Lakoff & Johnson, 1999). Although strategies for locating metaphors in a dream series through the use of content analysis go back several decades (Hall, 1953a), very little progress has been made in this direction. Lakoff (1993; 1997) presents new ideas for studying metaphors in dreams that provide additional starting points.
Another new avenue into this possible linkage might be found in "typical" dreams, such as flying under one's own power or finding oneself inappropriately dressed in public. Content analyses of hundreds of dream reports in journals kept during college courses demonstrate that such dreams account for less than 2% of dream life (Barrett, 1991; Domhoff, 1996), but several survey studies suggest that at least a significant minority of respondents claim to have had one or more of such dreams (Griffith, Miyago, & Tago, 1958; Nielsen, Zadra, Germain, & Montplaisir, 1999; Ward, Beck, & Rascoe, 1961). These dreams may be examples of "primary" metaphors, which are based on repeated correlations between two dimensions of experience that are common in childhood development, such as tasting something sweet (a physiological process) and experiencing pleasure (an emotion), leading to the metaphor that "Pleasing is Tasty" (Grady, 1999).
Consider dreams of flying under one's own power, which are experienced by a little over half of college students in two surveys, and said by them to be generally positive in feeling tone (Domhoff, 1996). Searching for a metaphor related to flying, the possibility arises that these dreams may be instances of the primary metaphor "Happiness is Up," as found in such expressions as "high as a kite," "walking on air," and "floating on cloud nine." This speculation also fits with the fact that people sometimes become apprehensive about falling during their positive flying dreams, just as people worry that they may "crash" or "have the air let out of their balloon" when they are too elated in waking life.
Similarly, it may be that dreams of appearing inappropriately dressed in public are instances of the metaphor "Embarrassment is Exposure," which is expressed through such well-known phrases as "caught red-handed," "caught with egg on your face," and "caught with your pants down" (Holland & Kipnis, 1994). It might be evidence for this conjecture that people who are asked to write down the dream in which they experienced the greatest feeling of embarrassment most often report one in which they are inadequately attired in a public place (Domhoff, 1996).
These two hypothetical examples aside, the few attempts to undertake systematic studies of metaphor in dreams suggest that most dreams do not seem to relate very obviously to primary metaphors (Hall, 1953a). Most dreams seem more like dramas or plays in which the dreamer acts out various scenarios that revolve around a few basic personal themes (Hall, 1947). They seem to be instances of the "thematic" point on the repetition dimension, that is, specific "episodes" or "examples" relating to more general emotional preoccupations, usually negative in nature. This means that less obvious forms of metaphor-- or other types of figurative thinking-- must be invoked if very many dreams are to be encompassed by the ideas of cognitive scientists.
These more complex dreams may rely on "resemblance" metaphors, which depend upon the perception of the common aspects in two representational schemas (Grady, 1999), or on conceptual blends that often start with basic conceptual metaphors and then are elaborated into highly novel thoughts (Grady, Oakley, & Coulson, 1999). Hall (1953a) has shown that blind analyses of a series of dreams can lead to very plausible and potentially verifiable inferences when figurative forms of thought relating to a major concern are utilized several times in the dream series. To take his best example, a young woman who provided a series of dreams had an especially striking one in which she was searching for her wedding gown because she and her husband were to be married again on their first wedding anniversary. However, she was very disappointed when she found the gown: it was dirty and torn. With tears in her eyes, she put the gown under her arm and arrived to the church, only to have her husband ask why she had brought the gown. She reports she was "confused and bewildered and felt strange and alone" (Hall, 1953a, p. 179).
Looking at the dream from a figurative point of view, Hall hypothesized that the state of the dress might express her conception of her marriage. In today's terms, the dream may be a conceptual blend based upon a metonymy. To test this hypothesis, Hall looked to see if there were other dreams in the series that might suggest the marriage is in difficulty, and there were several: (1) the stone from her engagement ring is missing; (2) her husband has tuberculosis; (3) one of her women friends is going through a divorce; and (4) a friend who is about to be married receives a lot of useless bric-a-brac for wedding presents. If the Hall/Van de Castle system had been available when this analysis was made, the case could have been improved by comparing the dreamer's aggressions-per-character ratio with her husband to the same ratio with other adult males. If it was higher with her husband than with other adult males, and if there was a lower rate of friendly interactions as well, then the metaphoric hypothesis would have been supported by means of a non-metaphoric content analysis.
The possibility that some dreams are based on figurative thinking provides a way for a neurocognitive theory of dreams to incorporate the interesting idea that past experiences are sometimes used as personal metaphors to express current conflicts that have similar emotions and feelings at their core (Kramer et al., 1987). This idea comes from a study of Vietnam veterans who had recovered from their post-traumatic stress disorder. However, they later came back to the Veterans Administration for help when war-related themes began to appear in their dreams in the face of new life stressors, such as marital conflict, conflicts with children, or work-related tensions. In effect, these new war-related dreams are conceptual blends that combine past experiences with aspects of the stressful situations the veterans are now enduring. The resemblance is in the similarity of the feelings in both the war and the new situation. "It's a war zone out there," they might be thinking, in relation to their current problems.
If dreaming is in part figurative, especially in terms of primary metaphors, resemblance metaphors, metonymies, and conceptual blends, then a neurocognitive theory of dreams could advance in parallel with new understandings in cognitive linguistics. However, it still would be necessary to do the same kind of thematic and Hall/Van de Castle content analyses of a dream series that have been carried out in the past in order to understand any given series of dreams. This is primarily because many resemblance metaphors and most conceptual blends are likely to be unique to the dreamer. In addition, several different primary metaphors use the same source domain, such as "vertical orientation," so contextual analysis would be necessary to decide among such possibilities as "Happy is Up," "More is Up," and "Control is Up" (Lakoff & Johnson, 1999, pp. 50-53).
In closing this discussion on cognition and dream content, it needs to be stressed that there is little or no systematic evidence that dreams make use of the vast system of figurative thought available in waking life to most individuals through a combination of developmental experiences and cultural heritage. Of all the possible linkages among the three areas of dream research suggested in this paper, the idea that dream content studies may provide bridges to the insights of cognitive scientists is by far the most speculative.
Discussion and Conclusion
There are other possible linkages among the three areas of dream research discussed in this paper, but enough has been said to demonstrate that there is now a large body of established empirical findings upon which it is possible to base a new neurocognitive theory of dreams. This theory builds on a recently discovered forebrain network of dream generation, links that network to the gradual development of dreaming in children, and then views dream content as the product of an interaction between the continuity and repetition principles, with an eye out for the possibility that the thinking during dreaming is at least in part figurative. Each of these linkages has something to contribute to an emerging synthesis on dreams, and a neurocognitive theory would be incomplete if it left out any of them.
Moreover, the research tools are now available to make possible the many necessary studies to test and develop the theory. The rapid advances in neuroimaging and neurochemistry are the most obvious examples of this point. The advent of personal computers and the constant improvements in software have made content analysis somewhat less labor intensive and far more accurate than it was in the past, especially through the development of a new spreadsheet that calculates all the Hall/Van de Castle content indicators (Schneider & Domhoff, 1995). It is also now possible to use a new search program to find single words, strings of words, or phrases in the many thousands of dreams available on the same site as the search program, and then to make detailed comparisons among types of dream reports (Schneider & Domhoff, 1999). This search program and its associated large collection of dream reports from a wide range of groups and individuals may prove especially useful for metaphoric studies.
As noted in the introductory paragraph, there is little or no scientific evidence to support any of the best-known theories of dreams (Domhoff, 1999; Domhoff, 2000b; Fisher & Greenberg, 1996; Foulkes, 1996a; Foulkes, 1999). Here it can be added that none of these theories seems able to deal with all three types of findings discussed in this paper. The developmental nature of dreaming and the repetition principle are especially difficult for them to assimilate. For people with an empirical or interdisciplinary bent, this may be a good time to consider testing the new neurocognitive theory of dreams sketched out in this paper.
Thanks to David Foulkes and Teenie Matlock for their many thoughtful suggestions after reading an earlier version of this paper, to Heidi Block, Melissa Bowen, Sarah Dunn, and Teenie Matlock for their help in developing the ideas about figurative thinking in dreams, to Mark Solms for answering last-minute questions about the neural network for dreaming, to the two anonymous reviewers who provided very helpful questions and critiques, and to Adam Schneider for his careful proofreading of the final manuscript.
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