Theories of Dreaming

Theories of Dreaming
The theory of dreaming most generally accepted, which offers an explanation of dreaming based on the physiology of REM sleep, is Hobson and McCarly’s (1977) activation-synthesis hypothesis. According to this hypothesis, dreams are the result of the forebrain responding to random activity initiated at the brainstem. This is demonstrated by the PGO waves that occur during REM sleep. Specifically, PGO refers to the pons, where the activity originates; the lateral geniculate nucleus of the thalamus, which is the area through which sensory information passes; and occipital areas, where visual information is processed. According to Hobson and McCarly (1977), this random activity, or noise, emanating from the pons, passes through similar sensory-relay stations as information from the environment, and is interpreted in a way that leads to the phenomenology of dreaming. Overall, this theory has received general support for some time because it fits well with physiological data and its explanation of dreaming appeals to a majority of peoples’ dream experiences, again, being somewhat haphazard and random. This theory posits that the bizarre nature of dreams is attributed to certain parts of the brain attempting to piece together a story out of what is essentially random information.
The activation-synthesis theory does make intuitive sense, based not only on how we generally remember and report information from dreams, but also on how difficult it is to piece together memories of a dream upon waking. Neuropsychological evidence points towards our tendency to confabulate stories that we believe to be true in order to fit together disparate pieces of information (Gazzaniga, 1985). If true, however, the supposedly random information that leads to dreaming would weaken the evolutionary analysis presented here. If there is no bias towards a particular type of information processed during REM sleep, then it becomes hard to imagine how dreaming could be selected for in an evolutionary context. Specifically if there is no rhyme or reason with regards to the content that makes up dreams, it becomes difficult to understand the advantage of experiencing such a haphazardly concocted virtual dream environment.
A more detailed analysis of dream content and the relation between REM sleep and dreaming, however, demonstrates that the activation-synthesis theory is
incomplete (Domhoff, 2000b). Although dreams tend to be rather bizarre, they are certainly not as disjointed as would be the case if this hypothesis were unilaterally true. In fact, large samples of dream reports from numerous studies point toward the fact that individuals see the majority of dreams as realistic and containing a connected storyline (Foulkes, 1985; Snyder, 1970; Domhoff, 2000a). This is something which should not occur if the information processed in dreams is truly random. Likewise, to be discussed below, certain information is differentially represented in dreams (Hall and Van de Castle, 1966).
Additional neuropsychological evidence reveals that the brainstem mechanism, which is a key ingredient in activation-synthesis theory, is not necessary for dreams to occur. Rather, work by Solms (1997, 2000) points towards the forebrain region as being crucial in the generation of dreams. If there is reason to believe that dreaming is not just the random processing of information, but instead there is some pattern to the types of themes present in dreams and the possibility that dreams can consist of cohesive story-lines, then it seems logical to investigate why these patterns exists and what purpose they serve. Before delving into these details on the functional aspects of dreaming, it is necessary to briefly describe more about the phenomenology of dreaming and how this could be reflected in the brain.