The running battle between activation-synthesis theorist J. Allan Hobson and psychoanalytic theorist Mark Solms since 1997, which heated up in a special issue of Behavioral and Brain Sciences in 2000, continued in books they separately published in 2002, and spilled into the pages of Scientific American in 2004, shows no signs of resolution (Hobson, 2000, 2002, 2004; Hobson, Pace-Schott, & Stickgold, 2000a; Solms, 1997, 2000b, 2004; Solms & Turnbull, 2002). It is the purpose of this article to critique all aspects of this debate. The article first outlines the substantive differences between the rival theorists and then presents several little-remarked similarities that give their debate some of its impact. It next discusses their claims in the light of systematic empirical findings on dreams from inside and outside sleep laboratories, concluding that the two researchers' most important assertions about the nature of dreaming and dream content are mistaken. In addition, this article shows that some of the men's speculations concerning the neurophysiology of dreaming are as questionable as their beliefs about dream content. Given the shortcomings in both theories, it is suggested that the search for a neurocognitive theory of dreaming has to be refocused.
Differences between Hobson and Solms
Hobson and Solms have three empirical differences, all of which involve brain stem and midbrain neurophysiological and neurochemical systems. Their first major empirical difference concerns what they believe to be the neurophysiological origins of dreaming. According to Hobson, dreaming has its origins in the same region of the pons that generates rapid eye movement (REM) sleep, which is said to produce relatively chaotic signals that activate the forebrain and force it to make the best sense that it can (a "synthesis") out of the noisy input it is receiving from various "phasic" (intermittent) events, primarily in the form of ponto-geniculo-occipital (PGO) spikes (Hobson & McCarley, 1977). This noisy input is asserted to be the key reason why dreams are allegedly bizarre and disjointed. More recently, Hobson has acknowledged that there is a greater degree of forebrain control of the REM mechanism than in his original theory, especially through the hypothalamus (Hobson, Pace-Schott, & Stickgold, 2000b). He has also altered the theory to reflect findings from neuroimaging studies, which reveal there is only a selective reactivation of the forebrain during REM, a result unanticipated by Hobson's theorizing (Braun et al., 1997; Maquet et al., 1996).
Despite the unexpected nature of these new findings, Hobson believes they support his belief that dreams are low-grade productions because the "emotional brain" (centered in the limbic and paralimbic regions) is among the areas that are reactivated, whereas what he has claimed are the exclusive executive and planning areas of the prefrontal cortex (the dorsolateral prefrontal cortex) are not reactivated. Solms (1997), conversely, has asserted that his research with brain-injured patients proves that dreaming is possible without REM. In conjunction with other research, his findings led him to locate the origins of dreaming in the ventral tegmental area of the midbrain, a few centimeters from Hobson's point of origin (Solms, 2000a).
This disagreement about the neurologic starting point for dreaming naturally has led Hobson and Solms to argue about the degree to which full-fledged dreaming, as defined by the presence of imagery and a sense of narrative plot, occurs outside of REM. Although Hobson recognized that there are at least some dreamlike reports from non-REM (NREM), he always has downplayed the frequency and quality of NREM dreaming. He also has tried to explain it away by saying that much of it may be a product of underlying REM mechanisms that do not always manifest themselves in the usual indicators used to detect and define REM periods (Hobson et al., 2000b). At his most extreme, he has asserted that "all of sleep is REM sleep (more or less)" (Hobson, 2000, p. 952).
Solms, as might be expected, readily cited longstanding evidence from sleep laboratory awakenings demonstrating that at least 10% of NREM reports are similar in their form and contents to reports from REM awakenings, which is enough to reject the tight relationship between REM and dreaming originally emphasized by Hobson (Foulkes, 1962; Herman, Ellman, & Roffwarg, 1978; Kamiya, 1961). More recent studies of dream reports from Stage 2 NREM late in the sleep period, many of which are indistinguishable from REM reports, reinforce that assertion (Antrobus, Kondo, & Reinsel, 1995; Cicogna, Natale, Occhionero, & Bosinelli, 1998; Fosse, Stickgold, & Hobson, 2004). Solms (2002, Chapter 6) also noted that the nightmarish dreams sometimes suffered by epileptics are due to complex-partial seizures in the limbic region during NREM, which indicates to him that REM should be seen as simply the best and most frequent trigger for the forebrain dream network, not as the only trigger, as in Hobson's theorizing. The final empirical difference between Hobson and Solms concerns the neurochemical mix that is assumed to modulate the process of dreaming and contribute to its unique properties compared with waking thought. According to Hobson, the lower levels of serotonin and norepinephrine during REM, when combined with high levels of acetylcholine, help to make the dreaming state very different from waking consciousness and give it several distinctive "formal" characteristics, such as distortions, unusual juxtapositions, sudden scene changes, and illogical reasoning, which are generally subsumed under the term bizarreness. For Solms, the dopaminergic system, originating in the ventral tegmental area, is the neurochemical basis for dreaming. He has stressed that this system is also the basis for the seeking system -- that is, the process that generates appetitive interests (Solms & Turnbull, 2002).
Although all three of these differences are highly technical and, in principle, resolvable through research findings, they are more than mere empirical disagreements because they are the battlegrounds for Hobson's and Solms's diametrically opposed views concerning the value of psychoanalytic dream theory. The two authors' clashing evaluations of Freud (e.g., Freud, 1900) give their argument its electricity, along with much of its appeal to those outside the field of dream research. For Hobson, the regularity of REM, the alteration between REM and NREM, and the brain stem basis for the REM-NREM cycle show that the Freudian emphasis on wishes, censorship, and the dream work is secondary at best, which means that Freud was wrong on all of his main hypotheses. As Hobson (2002) candidly admitted, "It is true that I want to discredit Freud emphatically" (p. 31). Solms, who came on the scene in the 1990s, saw his research with brain-lesioned patients as a rescue of Freudian theory from the all-out attack by Hobson and as providing the basis for an invigorating next step in psychoanalytic thinking that he has called neuropsychoanalysis. As one important building block for neuropsychoanalysis, he argued that the "seeking system" may be the basis for Freud's libido concept, which means that dreams are importantly motivated by sexual energy, just as Freud claimed (Solms & Turnbull, 2002, pp. 117, 312).
Similarities between Hobson and Solms
Although Hobson and Solms are vigorous proselytizers for rival views, they share several important underlying similarities that are essential to the nature and appeal of their argument. First, they share the idea that dreaming is a form of psychosis. After Solms and Turnbull (2002) outlined the effects of frontal lobotomies and antipsychotic drugs on the limbic white matter of the ventromesial quadrant of the frontal lobes, they wrote that "the functional anatomy of dreaming is almost identical to that of schizophrenic psychosis" (p. 213). They believed that this area is the "primary driving force" for dreaming because the "seeking system" (p. 203) courses through it.
Hobson (2002) agreed with the designation of dreaming as psychosis, stating that "psychosis is, by definition, a mental state characterized by hallucinations and/or delusions" and that dreaming is "as psychotic a state as we ever experience while awake" (pp. 98-99). However, he noted that the nature of the psychosis is not schizophrenia but "delirium" (p. 23), an organic brain disease defined by disorientation, visual hallucinations, illogical thinking, loss of recent memory, and confabulation. Hobson therefore administers a "mental status exam" for organic brain disease to his new patient, the dreaming mind. In dreams, as in delirium, consciousness is clouded, attention is distractible, intellectual functions are dull, perceptions are hallucinatory, cognition is illogical, emotion is unstable and uncontrolled, memory is poor, and thought processes are at a concrete, not a symbolic, level (Hobson, 2002, p. 23). This list of symptoms in effect spells out what Hobson saw as the unique "formal features" of dreams. On the basis of his diagnosis of dreaming as delirium, he indicated that it is "at least possible that dream content is as much dross as gold, as much cognitive trash as treasure, and as much informational noise as a signal of something" (Hobson, 2002, p. 101).
The extreme characterization of dreaming as a psychotic state not only distinguishes Hobson and Solms from most present-day dream theorists but links them to similar assertions over the centuries in psychiatry and philosophy, giving their debate a sense of profundity and deeper cultural resonance. They are building on one of the few "truths" endorsed by several hard-nosed scientists and a few famous philosophers. In addition, the notion that dreaming is either delirium or schizophrenia led Hobson and Solms to share an emphasis on the nature of dream content as bizarre and highly emotional. This characterization makes dreams highly exotic and feeds into popular stereotypes about them, thereby making the authors' disagreements of more general interest.
Most important in terms of this article, Hobson and Solms share a strong tendency to ignore or too readily dismiss the systematic empirical findings on dreaming and dream content, which are as essential to a neurocognitive theory of dreaming as are the neurophysiological issues Hobson and Solms emphasize. Instead of taking this literature into serious account as a way to constrain and test neurophysiological hypotheses, they have used their neurophysiological claims to explain what they take as the self-evident nature of dreams. Hobson (2000a) went so far as to dismiss this literature, stating that the study of dream content cannot be scientific. He therefore asserted that the focus of dream studies should be on the features or forms of dreams, meaning the presumably unusual nature of the perceptions, thoughts, and emotions in them that are similar to the symptoms of delirium. In less clinical terms, he meant that "dreams are visual and intensely emotional, have a peculiar logical quality, and times, places, and people are infinitely plastic and changeable" (Hobson, 2002, pp. 122-123). To buttress his claims about the nature of dreaming, he drew selectively on examples from his personal dream journal, calling these reports "REM dreams" on the basis of their length and content, even though they were not collected in a sleep laboratory (Hobson, 2002). In addition, as is shown in the next section, he has dismissed studies of the formal features of dreams carried out by other investigators.
As for Solms (1997), he has simply assumed that Freudian case examples of dreams from clinical practice reveal what researchers need to know about dream content. He has never discussed studies of dream content, except to ridicule "some rather absurd conclusions" (p. 70) in a study of the dream content reported by patients with chronic brain syndrome. After correctly reporting that the study found that these patients dreamed more often of women, family members, and friendly social interactions than a control group did, he concluded that "claims such as these do not warrant serious scientific consideration" (p. 70).
As a specific example of how Hobson and Solms have asserted conclusions rather than looking at the literature on dreams, Hobson and McCarley (1977) assumed that there is a large amount of movement in dreams and that dreams of flying under one's own power, which are allegedly one typical example of this ubiquitous movement, are a "logical, direct, and unsymbolic way of synthesizing information generated endogenously by the vestibular system in D (dreaming) sleep" (p. 1339). In addition, they asserted that there are frequent "bizarre juxtapositions" because of the "heightened degree of simultaneous activation of multiple sensory channels in dreaming as compared with waking" (p. 1339).
Similarly, Solms claimed that his findings with neurologic patients, which demonstrate the importance of the forebrain in dreaming, disprove Hobson's conclusion that dreams are not psychological and ideational, thereby reestablishing the credibility of Freud's (1900) theory of dreams. He made this assertion even though he presented no evidence relating to psychological meaning in dream content. To his way of thinking, it "might still be possible to argue that dreams are 'mindless' and 'motivationally neutral'" (Solms & Turnbull, 2002, p. 196) if he had not dissociated the neural substrate for dreaming from the brain stem. However, contrary to Solms's assertion, a refutation of what Hobson claimed about the origins of REM dreaming has nothing to do with whether dreams are meaningful, an issue that has to be studied on the mind side of the brain-mind equation -- that is, in terms of the relationship of dream content to waking psychological variables. Hobson's claims and Solms's counterclaims are ideal examples of how the two have drawn conclusions about dream content from neurophysiological arguments while ignoring the need to study dreaming and dream content at a cognitive level.
Moreover, Solms was prepared to abandon Freud's (1900) psychological concept of "censorship" on the basis of the deactivation of the dorsolateral prefrontal cortex during sleep. Because this area is thought to be important to the executive functions of waking thought, Solms and Turnbull (2002) asserted that Freud "may have been wrong" about censorship because "the apparent illogicality and bizarreness of dreams may be due to the inherently 'regressive' nature of the dream process" (p. 215), which means that dreaming happens in the back part of the cortex because the prefrontal cortex is not very active. This indicates that there may be "no need to introduce the additional function of censorship"; that is, "the symbolic transformations to which Freud drew attention might, therefore, simply be the product of unconstrained parietal-lobe mechanisms operating in reverse" (p. 215). Once again, a cognitive issue has been decided on the basis of neurophysiological conclusions, without any study of the actual content of dream reports to discern whether dreams are symbolic.
A final similarity between Hobson and Solms is that they share a need for each other to polarize the general theoretical debate and keep it focused on their respective theories. Solms, for example, actually attributed the decline of Freudian dream theory to Hobson and his activation-synthesis theory, an argument that overlooks the many reasons why Freudian dream theory was in decline independently of Hobson because of the findings of empirical dream research well before Hobson presented his theory (Domhoff, 2004). Only by blaming Hobson for this decline can Solms argue that his own findings have restored Freudian theory to its rightful place. Without Hobson, Solms would have to confront the empirical literature on dream content discussed in the next section.
As for Hobson, who came to the attention of science writers and the general public primarily because of his anti-Freudian stance, it is useful to him to once again have a Freudian who is willing to argue with him. It justifies the space he reserves for passe´ attacks on Freud (e.g., Freud, 1900) while ignoring the fact that virtually all dream researchers, including his most convincing critics, are non-Freudians (Antrobus, 1978, 2000a, 2000b; Foulkes, 1985, 1999).
Systematic Findings on Dreaming and Dream Content
Although Hobson and Solms have very different explanations for why dreams are supposedly illogical and disjointed, they do not doubt their common portrait of dreaming as psychotic, bizarre, and fraught with emotion. It is therefore useful to see what descriptive empirical studies, unburdened by strong theoretical preferences and biases, have shown about dreaming and dream content. For most empirical dream researchers, the best starting point for gaining an insight into the nature of actual everyday dreaming is in the sleep laboratory, where immediate awakenings from REM and NREM provide the maximum possibility of accurate recall. Detailed discussions of studies relating to the psychophysiology of dreaming can be found in Antrobus (2000a, 2000b) and Pivik (1986, 1991), and a discussion of studies of dream content can be found in Domhoff (2005), so these studies can be summarized more briefly here.
Drawing on the same psychiatric sources that later provided inspiration to the theorizing by Hobson and Solms, several laboratory dream researchers of the late 1950s and early 1960s explored the idea that dreaming might throw light on psychosis. They focused especially on a preliminary finding that depriving participants of REM sleep (which was called dream deprivation at the time) seemed to increase their hallucinatory thinking during the day (Dement, 1960; Dement & Fisher, 1963). However, it was soon shown that REM deprivation did not increase the cognitive pathology of schizophrenic patients (Zarcone, Gulevich, & Pivik, 1968) or have any negative effects on the thought patterns of nonclinical participants. To the contrary, REM deprivation seemed to be helpful for some depressed patients (Lewin & Singer, 1991; Pivik, 1986; Vogel, 1975), and patients on high doses of monoamine oxidase inhibitor antidepressants lost almost all REM sleep with no apparent ill effects, even after several months (see Vertes & Eastman, 2000, for a summary). As Pivik (2000) later concluded in an overview of the psychophysiology of dreams, if there is a relationship between dreaming and waking hallucination, "it remains elusive because studies of the sleep and dreams of mentally ill persons have been unable to demonstrate a consistent increase in adverse effects, either physiological or psychological, during wakefulness as a consequence of REM deprivation" (p. 493).
The early laboratory dream researchers also searched in vain for linkages between specific physiological events and evidence of bizarreness in dream content. For example, Moskowitz and Berger (1969) immediately awakened participants who were showing unusual eye movement patterns during a REM period but were unable to find any correlations with the dream reports. Other studies looked with little or no success for physiological correlates of discontinuity or bizarreness in reports from immediate awakenings (Foulkes, 1996). Contrary to what Hobson predicted, "the presence or absence of phasic activity is not a strong predictor of the hallucinatory or emotional quality of mentation" (Pivik, 1991, p. 234). In a direct critique of Hobson's ongoing claim about the way PGO spikes supposedly influence dream content, Antrobus (2000a) expressed his dismay that Hobson "continues to attribute bizarre cognition to chaotic pontine activation despite the fact that no experiments have supported this association and furthermore, bizarre mentation is frequently observed in states where PGO activity is minimal" (p. 906).
In the context of these studies showing how difficult it has been to identify any of the relationships between neurophysiology and dreaming that are taken as certain by Hobson and Solms, studies of the actual content of dream reports become of even greater importance in terms of their emphasis on bizarreness and emotionality. One of the earliest and largest of the laboratory studies (Snyder, 1970; Snyder, Karacan, Tharp, & Scott, 1968) used 635 REM dream reports from 58 young adult men and women; the dreams were collected "for a variety of experimental purposes" (Snyder, 1970, p. 127) in a series of investigations over a period of 7 years between 1960 and 1967 at the National Institute of Mental Health in Bethesda, Maryland, and the Downstate Medical Center in Brooklyn, New York. The overall finding was that "dreaming consciousness" is "a remarkably faithful replica of waking life" (Snyder, 1970, p. 133), a far cry from the portrait of the typical dream painted by Hobson and Solms. The overwhelming majority of settings were commonplace and often familiar to the dreamer; only 5% were categorized as exotic. The most frequent activity was talking, which appeared in 86% of the medium-length reports and 100% of the long reports. By contrast, active exertion (e.g., running, playing a sport, fighting) occurred in only 15%-20% of the reports, which hardly fits with Hobson's belief that movement is pervasive in dreams because the vestibular system is activated during REM sleep.
The investigators made a series of ratings for coherence, dramatic quality, and bizarreness, with bizarreness defined as any events outside the conceivable expectations of waking life. They found that 60%-80% of the dreams were highly coherent on a 3-point scale, as compared with less than 5% that were rated as low on coherence. Three fourths of the dreams had a nil or low degree of drama on a 4-point scale, and less than 10% were high on drama. The majority of dreams were rated as having little or no bizarreness on a 4-point scale; in terms of only the longest reports (because they were more frequently rated as bizarre), 50% were rated as having no bizarreness, 30% had a low degree of bizarreness, 8% had a medium degree, and 2% had a high degree (Snyder, 1970).
The researchers also made a search for "typical" dreams, a term that encompasses a handful of common themes that many people say, in response to questionnaires, that they have experienced, such as failing an exam, appearing inappropriately dressed in public, or being able to fly under their own power. Although there were very few instances of any of these themes, the finding of the greatest relevance is that there was only one flying dream, which contradicts Hobson's assertion that flying is often present in dreams because the vestibular system is so active (Snyder, 1970, p. 148).
Bizarreness in Laboratory Dream Reports
The apparent lack of highly unusual dream content in REM reports was investigated in more detail in a study of 16 young adult women who spent two consecutive nights each in the lab and answered questions about the familiarity and likelihood of specific dream elements after an average of four REM awakenings per night (Dorus, Dorus, & Rechtschaffen, 1971). The investigators concluded that their results "emphasize the rarity of the bizarre in dreams" (p. 367). For example, the figures for the most improbable category of events never experienced by the dreamer in waking life were 4.9% of all physical surroundings, 1.3% of all characters, and 6.8% of all activities and social interactions. When the authors carried out global ratings of each dream for overall bizarreness, they found that only 8.9% were highly improbable by waking standards.
As one part of a comprehensive laboratory investigation of dream content in Switzerland, based on 500 REM dream reports from 44 participants (26 women, 18 men) who spent 16l nights in the laboratory, Strauch and Meier (1996) examined a subsample of 117 dreams with a variety of bizarreness scales. Contrary to what might be expected on the basis of Hobson's emphasis on the bizarre features of dreams, it was found that unusual dream content, ranging from the improbable to eccentric actions by characters to mild violations of social or cultural standards, were more than twice as frequent as bizarreness in dream structure, such as sudden appearances or disappearances or sudden scene changes. There were no bizarre elements of any kind in 23.9% of the reports, and there was only one bizarre element in another 39.3%. The authors reported that they "collected only very few dreams in which coherent thought and experience were entirely lacking, remained totally unintelligible, or were even seemingly disturbed" (Strauch & Meier, 1996, p. 103).
Emotions in Laboratory Dreams
The issue of emotions in dreams was investigated in detail in a study of 17 young adults (9 women, 8 men) over two nonconsecutive nights. The participants were quizzed carefully after each awakening as to the presence of emotions and the appropriateness of the emotion to the content. Drawing on ratings by both participants and naive judges, the authors concluded that about 30% of the dream reports had no affect (Foulkes, Sullivan, Kerr, & Brown, 1988). Although the type of emotion was overwhelmingly appropriate to the dream situation when it occurred, there was no emotion in 17% of the cases in which there would have been some emotion in a similar waking situation.
In the Swiss study by Strauch and Meier (1996), participants were asked how they felt during the dream and how intense their feelings were. On the basis of all 500 REM dream reports, the authors found that 26.4% of the dream reports had no emotions, 23.4% had general mood states, and 50.2% had specific emotions. Overall, a variety of negative emotions appeared twice as often as positive ones, with the intensity of the emotions in a middle range -- that is, rarely extremely mild or extremely intense. By and large, the participants "registered the same emotional reactions that they would have had while awake and facing a similar situation" (Strauch & Meier, 1996, p. 95), but some dreams lacked the emotional involvement that would have been part of the same experience in waking life. On the basis of the significant number of dreams without emotions, Strauch and Meier concluded that "the interesting observation that many dreams did not cause emotional reactions stands in contrast to a conception that emotions are crucial to the dream experience" (p. 95).
A third study, focused exclusively on the issue of emotions, reported findings similar to those in the first two studies. Focusing on REM reports from 9 Norwegian participants (7 women, 2 men) whose sleep stages were monitored in their home via a portable polysomonographic machine, the authors discovered that 26% of the reports had no emotional elements, which is almost exactly the same as the findings in the two laboratory studies just cited (Fosse, Stickgold, & Hobson, 2001). Moreover, emotion was rated as low in 18% and medium in 28% of the remaining dreams in this study, leaving only 28% of the dream reports in this study with high emotional content.
Hobson's theory cannot readily explain the finding in these three studies that emotions are absent from about one fourth of all REM dream reports and that sometimes there are no emotions when they would have been present in waking life. Nor does the distribution of emotional intensity fit with the kind of portrait that Hobson has painted of all dreams. Solms, conversely, had no problem with findings about the absence of emotions, because Freud (1900) wrote that the dream work often "mutes" the "tonality" of a dream, which means that "the dream has fewer and weaker affects than the psychical material from which, as adapted, it has emerged" (p. 304). Instead, the problem for Solms was in the appropriate nature of all the emotions in these studies, because Freud (1900) concluded that "there are plenty of dreams in which the opposite occurs: an intense expression of affect will make its appearance accompanying a content that does not seem to offer any occasion for the release of affect" (p. 299).
Taken together, these several descriptive laboratory studies provide a consistent picture. If REM dreams from awakenings in the lab are the best evidence available on the nature of dreams, then these findings raise fatal objections to the claims by Hobson and Solms. However, are REM dream reports actually a good sample of dream life? Perhaps people are too inhibited in the lab to have their usual bizarre and highly emotional dreams. That is exactly what Hobson et al. (2000a) have insisted in dismissing the results of laboratory dream studies in general, although Hobson never has challenged the investigations just cited that were specifically focused on bizarreness or emotions. It therefore becomes necessary to look at studies comparing laboratory and home dreams.
The General Nature of Home Dreams
Despite early claims to the contrary by Domhoff and Kamiya (1964), several later studies of lab and home dreams from the same participants demonstrated that there are not many differences in favor of home dreams, even when there are no controls for the possibility of selective memory for more emotional and bizarre dreams at home (Domhoff & Schneider, 1999; Heynick & deJong, 1985; Hunt, Ogilvie, Belicki, Belicki, & Atalick, 1982; Strauch & Meier, 1996; Zepelin, 1972). Furthermore, most of these differences disappeared when the proper controls were introduced in the two best studies of the issue (Foulkes, 1979; Weisz & Foulkes, 1970). It is notable that there were no differences between lab and home dreams in two different studies of bizarreness (Hall, 1966b; Hunt et al., 1982). The one regular difference in the two types of reports seems to be in the realm of hostile and aggressive dream elements, which occurred more frequently in the home dream reports of young adults in two different studies (Domhoff & Schneider, 1999; Weisz & Foulkes, 1970). However, aggressive interactions, many of which simply involve hostile thoughts, criticisms, and rejections, do not seem to be what Hobson and Solms had in mind when they characterized dreaming as a psychotic state and dream content as bizarre.
The fact that laboratory and home dreams do not differ very much except on aggression opens the way to consider the results from studies using large samples of home dream reports collected from young, college-educated adults in a wide range of colleges and universities. These studies go back as far as the 1890s, when psychologists made careful studies of many dozens of their own dreams after recording them following night and morning awakenings (e.g., Calkins, 1893; Weed & Hallam, 1896). As Snyder (1970), the lead investigator in the Bethesda-Brooklyn laboratory investigation of 635 REM dream reports, later concluded, the study's findings "only confirm" (p. 150) these first results from outside the laboratory, which were soon lost from view in the wake of the sensationalistic psychoanalytic pronouncements about dreams. The many studies since that time are presented in detail elsewhere and need not be reviewed here; they reveal regularities by gender, age, culture, and individual personal concerns that make sense in terms of waking thoughts and behavior, once again contradicting the idea that dreams are psychotic ramblings (Domhoff, 1996). They also show that dreams of flying are as rare outside the laboratory as they are inside it, which once again refutes Hobson in his assertions about both the inhibitory nature of the laboratory and the prevalence of flying dreams (Barrett, 1991; Domhoff, 1996, p. 198).
To the degree that the dream reports of psychiatric patients can be given any credence in the light of many possible confounds, they are not very different from those of nonpatients. The biggest difference is that psychiatric patients tend to have fewer characters in their dreams who are identified as friends (Domhoff, 1996; Kramer & Roth, 1973, 1979). They also showed fewer friendly interactions in some studies and more physical aggressions in other studies, but none of the studies noted any unusual degree of bizarreness (see Domhoff, 1996, pp. 184-188, for a summary of the major studies on this issue; Hall, 1966a).
However, studies of large samples of home dream reports from college students have shown that dreams are not a perfect simulation of everyday life. For example, in Hall and Van de Castle's (1966) normative samples of 500 men's and 500 women's dream reports, 7% of the familiar settings in men's dreams and 14% of the familiar settings in women's dreams were in some way different from the way the settings actually were in waking life, and almost 2% of the characters were dead or imaginary or turned into another character. It is also noteworthy that about one third of all dream reports contain misfortunes, which range from being lost to illness to the death of a loved one, and that the negative emotions of sadness, anger, confusion, and apprehension, when taken as a whole, greatly outnumber the expressions of happiness. Findings such as these show that dreams are not a complete replica of waking life.
Nor are the results on the frequency of emotions in home dream reports different from what has been found in laboratory studies. For example, in an early study of emotions in 1,000 dream reports, in which the dreamers made judgments about the emotional content of their dreams, 23% of the dreams were said to be without feeling tone (Hall, 1951). This figure is very similar to the finding of no affect in 30%, 26.4%, and 26% of the dreams in the three REM-based studies discussed earlier in this section (i.e., Fosse et al., 2001; Foulkes et al., 1988; Strauch & Meier, 1996). To the degree that there are any disagreements with these conclusions, they come from studies by Hobson and his coworkers. They reported far more emotions in home dreams when the participants rated their dream reports line by line, after the reports were written out, for the emotions that supposedly were present. The possible emotions that might appear were listed in separate columns that were to be marked if they were deemed appropriate (Kahn & Hobson, 2002; Kahn, Pace-Schott, & Hobson, 2002; Merritt, Stickgold, Pace-Schott, Williams, & Hobson, 1994). Hobson thereby found as much as 10 times the amount of emotion reported in other studies, but his procedure probably inflated the amount of emotion actually experienced, because there are strong demand characteristics attached to the task of going back through a written home dream report line by line with instructions to recall and write down the emotions that were present for that part of the dream. Given the contrary results presented in other studies inside and outside the laboratory and the possibility that his data are unreliable, Hobson's conclusions cannot be given the importance that he assigned to them until they are replicated by independent researchers using dreams that are collected and analyzed in a manner that guards against the possibility of confounds.
Bizarreness in Home-Reported Dreams
As one might expect by this point, there are also differences between the Hobson group and other dream researchers on the extent of bizarreness in home dream reports. This was a critical issue for Hobson (2002) because of his argument that many of the studies discussed throughout this section are irrelevant to his theorizing. As noted earlier, he has asserted that bizarreness is in the features of dreams -- that is, in the unusual nature of the perceptions, thoughts, and emotions-- which means that "times, places, and people are infinitely plastic and changeable" (pp. 122-123). However, in studies that focus on clearly impossible events of the kind implied by Hobson's quoted comment, the figure is 10% of dreams or less for large samples of both REM and home dreams (Dorus et al., 1971; Hall, 1966b; Snyder, 1970). When sudden scene changes, uncertainties, confusion, and small distortions are included, as they are in scales used by Hobson and his colleagues (Rittenhouse, Stickgold, & Hobson, 1994) and Revonsuo and Salmivalli (1995), the figure rises to between 40% and 60%.
One of the most frequent bizarre elements that Hobson and his coworkers (e.g., Rittenhouse et al., 1994) have found in dreams is the number of abrupt scene changes, which occurred in 34% of 200 dreams in one of their studies (Rittenhouse et al., 1994). However, not all studies have agreed that there are frequent discontinuities within dream reports. In a detailed study of this issue, Foulkes and Schmidt (1983) divided REM dream reports into a series of "temporal units," defined by the appearance of a new activity in the dream, such as the sequence of coming out of school/opening the gate/children saying goodbye to each other/walking down the street. They found that only one in eight temporal transitions was accompanied by a discontinuity in both setting and characters. They argued that the relatively small discontinuities in dreams are consistent with, and probably necessary for, the considerable degree of narrative and thematic development that is found in most REM reports.
Whatever the exact number of abrupt scene changes is within dreams, it is not obvious that these and other unusual events in dreams are inherently bizarre if they are compared with either the stories people are familiar with in waking life or waking thought flow. Hobson has judged dreams as psychotic on the basis of waking reality, noting that some of the events that happen in them could not happen in reality. However, such events do happen in many of the stories, fairy tales, and videos that people experience from preschool onward, and metamorphoses and blended characters are standard features of imaginative productions, as are animals that talk and sudden changes in settings. If waking imaginal products are used as a baseline, it is more likely that dreams are like stories than that they are a form of psychosis.
Even everyday waking thought has more of the features that Hobson saw as unique to dreams than he has acknowledged. In a study comparing REM reports with waking streams of thought from the same participants when they were sitting in a darkened room, it was found that there were more abrupt scene changes in the waking sample than in the REM reports (Reinsel, Antrobus, & Wollman, 1992). In everyday thought sampling with large numbers of people by means of pagers, about one third of all thoughts were judged by participants as spontaneous, meaning that they just popped into the participants' mind (Klinger, 1999; Klinger & Cox, 1987-1988). Further, 21% of thoughts have aspects that are physically impossible, and many thoughts are judged as disconnected. There are also wide individual differences in how much thinking is said to be deliberate or spontaneous. For two thirds of the participants (Klinger, 1999), the majority of their thoughts are deliberate and intentional, but for the other one third, the majority of their thoughts are spontaneous. When researchers are judging the bizarreness of dreams, the proper baseline therefore must be the same person's waking thought patterns, as randomly sampled by means of a pager (cf. Bednar, 2000, p. 909; Chapman & Underwood, 2000, p. 917).
Taken as a whole, then, the results from laboratory and home studies on bizarreness in dreams do not provide evidence for Hobson's (e.g., Hobson, 2002) theoretical assertions. Contrary to his belief that dreams are "cognitive trash" (p. 23) best characterized by the symptoms of delirium, including illogical cognition, unstable emotion, and dull intellectual functions, dreams are most often reasonable simulations of waking life that contain occasional unusual features in terms of settings, characters, or activities (Dorus et al., 1971; Foulkes, 1985; Hall & Van de Castle, 1966; Snyder, 1970).
Findings on dreaming and dream content with children awakened in the sleep laboratory are as inconsistent with the theories put forth by Hobson and Solms as are the findings on the dreams of adults. These studies, one longitudinal over a 5-year period with 46 children between the ages of 3 and 15, the other a cross-sectional replication with 80 children ages 5-8, revealed that little children do not dream often or well and seldom report any dream content that is bizarre or emotional (Foulkes, 1982, 1999; Foulkes, Hollifield, Sullivan, Bradley, & Terry, 1990). Generally speaking, the development of dreaming and dream content seems to parallel cognitive and emotional development during childhood. The fact that dreaming is a gradual cognitive achievement was completely unanticipated by both theorists and is not easily explained by either of them.
Incredulous that children's dreams might lack in complexity, bizarreness, or emotions, Hobson et al. (2000a; Resnick, Stickgold, Rittenhouse, & Hobson, 1994) denigrated these discoveries by saying that the children were inhibited in the laboratory and are unable to articulate adequate reports of their dream experiences at a young age, but Foulkes (1979, 1982) has proven otherwise on both counts (see Domhoff, 2003, for a detailed discussion). The absence of dreaming in preschool children also raises difficult questions for the psychoanalytic conclusion that dreams are the guardian of sleep. It is hard to accept this idea if dreaming is not a regular part of sleep until ages 8-9.
The Neurophysiology of Dreaming
Because dream content is very different from what Hobson and Solms have assumed to be the case, they must be incorrect in their neurophysiological speculations. The cognitive side of the equation -- the evidence from studies of actual dreaming and dream content -- does not fit with the "brain" side of the equation, as they have imagined it to. In fact, as this section shows, there is indeed reason to doubt Hobson's and Solms's claims about the neurophysiology of dreaming. In Hobson's case, his neurophysiology is mistaken, because the brain stem signals may not be as noisy as he believed. One of Hobson's most prominent neuroscience critics noted that she did not "know of any physiological evidence that the brain stem activation and stimulation of the forebrain is chaotic and would thus impose a chaotic influence on the cortex in dreams" (Jones, 2000, p. 956). In fact, there is every reason to believe that "circuits within the brain stem, as in the spinal cord, are highly ordered, so that specific motor patterns such as locomotion, chewing, and vestibulo-ocular nystagmus, are generated there in a repetitive, rhythmic, and highly predictable manner" (Jones, 2000, p. 956). The same holds for more complex behaviors generated there. Jones's conclusions are consistent with the earlier cited observations demonstrating that unusual eye movement patterns and other kinds of phasic bursts during REM do not correlate with bizarre dream content when the dreamer is immediately awakened (Antrobus, 2000a; Moskowitz & Berger, 1969; Pivik, 1991).
The findings on dream coherence also imply that Hobson must be incorrect about the nature of the neurochemical environment during REM dreaming or about its effects on dreaming. As might be expected, then, his critics have agreed that the modulatory environment during REM is more complex than he allowed (Gottesmann, 2000, 2002; Perry & Piggott, 2000). It may not be a matter of only the contrast between lower levels of serotonin and norepinephrine, on the one hand, and waking levels of acetylcholine, on the other, as he concluded. At the least, the absence of serotonin, norepinephrine, and histamine is important, along with waking levels of both acetylcholine and dopamine, with the dopamine perhaps having more impact because its usual inhibitors are at low levels (Gottesmann, 2002). Furthermore, the role of gamma-aminobutyric acid is more important than Hobson's theory allows, although its role is yet to be fully understood (Siegel, 2000, pp. 119-120). Even more generally, the number of neurotransmitters involved and the complexity of their interactions seem to grow with each passing year (Pace- Schott, 2003).
Whatever the exact neurochemical environment turns out to be at those times when the brain is activated in a manner that makes it possible for dreaming to occur, it seems likely from the nature of most dream content that Hobson has continued to underestimate the degree of cortical control in dreams. Once again, Jones (2000) stated unequivocally that she did "not know of any physiological evidence that the cortex has no control over the brain stem or over the central activity of dreams" (p. 956). Further, "corticofugal outputs reach the entire brain stem as well as the spinal cord, influencing the very neurons shown to be critical for the initiation and maintenance of REM sleep in the pontine reticular formation" (Jones, 2000, p. 956). Another prominent neuroscience researcher concluded that:
It is also noteworthy that eye movements and PGO spikes are reduced to stereotypic and highly ordered patterns in decerebrate cats, which suggests that "the cortex thus appears both to control and introduce complexity to the brain stem activity" (Jones, 2000, p. 956; cf. Siegel, 2000, p. 121).
In keeping with these cautions, the injection of cholinergic agonists into central amygdaloid nuclei in cats shows that these agonists exert great modulatory power on the brain stem, doubling the amount of REM per night over a period of 5 days (Calvo, Simon-Arceo, & Fernandez-Mas, 1996). Furthermore, the results of imaging studies with human participants suggest that the extended amygdala complex may be closely related to and interact with the medial cortical regions that are activated in REM, including the orbital and ventromedial surfaces of the frontal cortex, which are known to be crucial for complex emotional and perceptual control during waking (Fosse et al., 2001; Maquet, 2000; Maquet et al., 1996).
Results such as these help explain why Hobson overestimated the presence of "unstable" and "uncontrolled" emotion; he focused too readily on the brain stem and its reactivation of the limbic region in REM, thereby downplaying the degree to which the limbic region is under intrinsic control. Hobson has made an unjustifiable leap from the relative deactivation of the dorsolateral prefrontal cortex to an alleged lack of sensible cognitive controls in most, if not all, dreams. Even though the dorsolateral prefrontal cortex is central for higher order cognition, other regions of the prefrontal cortex that remain activated are known to contribute to complex cognitions. These regions include the anterior cingulate, important for control of sustained attention, and emotional and perceptual control regions in more medial and ventral parts of the prefrontal cortex already mentioned in the previous paragraph (Braun et al., 1997; Maquet, 2000; Maquet et al., 1996; Nofzinger, Mintun, Wiseman, Kupfer, & Moore, 1997). These regions are generally thought to subserve cognitive processes for schemas, semantic memory, self-understandings, and general world knowledge. In effect, Hobson has downplayed the neurocognitive systems that may be important for dreaming; his main cognitive-level concept is simply "synthesis."
As for Solms, he also has overstated the bizarreness of dreams. Dream content seems almost as far from schizophrenia as a well-crafted short story and as appropriate in emotions as are most waking situations. The coherent nature of most dreams refutes Solms's belief that dreams are bizarre because of low levels of activation in the prefrontal cortex. However, he recently came close to conceding that the neurochemical modulation during dreaming is more complex than he originally thought (Solms, 2002), acceding to the argument put forth by Gottesmann (2002). Solms has labored mightily to try to prove that Freud's (1900) theory of dreams is consistent with modern-day neurophysiology, but he has never once looked to see whether it is consistent with 50 years of empirical dream research at the psychological level (see Domhoff, 2003, for a complete presentation of this evidence in relation to Freudian theory).
Discussion and Conclusion
Building on the lesion and imaging studies published in the 1990s, which created some new interest in scientific dream studies after many years in the doldrums, Hobson and Solms unfortunately used the occasion to revive the longstanding battle between Freudians and those anti-Freudian neurophysiologists who do not take the cognitive level seriously enough. They also revived claims about the generally psychotic nature of dreaming that had been abandoned by the early 1970s, at the latest, by laboratory dream researchers. Moreover, as this article has demonstrated, Hobson and Solms already had been refuted on several of their theoretical points of concern by the accumulation of systematic evidence on the actual nature of dreaming and dream content. None of their neurophysiological speculations, which also turn out to be dubious on neurophysiological grounds alone, has much credibility, because the main findings on dream content are at odds with them.
If there is to be an eventual synthesis of dream findings with neurophysiological results, it cannot be based on Hobson's cognitively impoverished framework or Solms's attempt to revive psychoanalysis as neuropsychoanalysis. On the basis of the findings to date, it is better, on the one hand, to begin with an attempt to determine the features that dreaming may share with both normal waking cognition and waking hallucinatory thinking and, on the other hand, to blend that understanding with a thorough grounding in the systematic findings on dream content. Within this context, perhaps more precise hypotheses could be formulated that might make it possible to use the new technologies and findings developed in the neurosciences over the past 15 years to move beyond the two orthodoxies represented by Hobson and Solms. It then might be possible to incorporate the unusual features of dreaming and dream content, stressed out of all proportion by both Hobson and Solms, into a new neurocognitive theory of dreams.
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