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
Evolutionary Psychology – ISSN 1474-7049 – Vol - ume 3. 2005. 63 -The Role of Dreams in the Evolution of the Human Mind

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.