REM Sleep = Dreaming: Only a Dream
Department of Psychiatry, University of Medicine and Dentistry of New Jersey,
671 Hoes Lane, Piscataway, NJ 08855
University of California, Davis and VA Northern California Health Care System
There is an ironic contradiction in current
literature on sleep and dreaming. Those who have
conducted controlled research, or who have evaluated
this research objectively, know that equating REM
sleep with dreaming is no longer a supportable
proposition - if it ever was. On the other hand, many
neurophysiologists ignore the accumulated body of
rigorous psychophysiological data and describe their
research on REM sleep as studies of the
"neurophysiology" or "biochemistry" of dreams.
Given the peculiar hierarchy of scientific
authority, and the allure of linking psychology to
physiology, it is these latter scientists that tend to
dominate current opinion. This produces several
unfortunate consequences. First, it suggests to our
students that it is OK is ignore scientific data that does
not fit one's prejudices. It also misleads the public on a
topic of enormous lay interest. But its most destructive
effect is to impede research progress: the daunting
complexity of one of the most interesting problems in
human brain-behavior relations is being sacrificed in
favor of an outmoded (and false) simplification.
In the remainder of this brief essay, we outline
the evidence that compellingly refutes a REM=dream
isomorphism. A more detailed review will be
Goodenough et al. (1959) appear to have been
the first to seriously question the REM=dreaming
equivalence. They reported that a group of subjects
(Ss) who reported frequent spontaneous recall of
dreams at home had a high (53%) rate of dream recall
in experimental awakenings from NREM sleep. Three
years later, Foulkes (1962) reported a similarly high
(54%) rate of dream reports from NREM awakenings
in Ss unselected with respect to dream recall. With
reports of "thinking" included as dreams, this rate
jumped to 74%, close to the ~80% usually obtained
from REM awakenings. Foulkes did, however, find
qualitative differences between REM and NREM
dreams. Narratives from NREM awakenings tended to
have a lower incidence of affective events and visual
images than those from REM. This observation, which
remains influential in textbooks and other literature,
turned out to be misleading, as we discuss below.
Foulkes and Vogel's early study (1965) of
mental activity at sleep onset further challenged the
REM=dream equivalence. They found that dreamlike
reports, often similar to those obtained from REM,
could be obtained from awakenings at sleep onset.
These reports were common during descending stage 1
and 2, and could occur in the presence of alpha.
Although the hypnagogic reports as a group tended to
be shorter and to lack the visual continuity of many
REM reports, they described sleep onset narratives
that seemed indistinguishable from the dreamlike
reports Pg. 10 obtained from REM.
Early evidence cited in support of a
REM=dream isomorphism was an apparent
correlation between the pattern of rapid eye
movements during REM sleep and that which would
be expected if the subject had been scanning the dream
images he later reported (Dement and Kleitman, 1957;
Roffwarg et al., 1962). However, initial positive
findings were not confirmed in later, better-controlled
studies. Moskowitz and Berger (1969) found that only
18 of 56 blind matchings were correct, little above the
fourteen expected by chance. Studies by Firth and
Oswald (1975) and Jacobs et al. (1972) also failed to
find a consistent relationship between eye movements
and dream imagery. Koulack (1972) reviewed the
evidence on this question and concluded that "the
notion of a constant isomorphic relationship [between
eye movements and dream imagery] is untenable."
Nevertheless, one still finds contemporary texts that
describe the scanning hypothesis as confirmed. We
would also like to reiterate here our hypothesis that the
eye movements of REM hold no special significance
for the psychology of this state. The effector response
to neuronal firing in the oculomotor nuclei - eye
movement - does not cause arousal. In contrast, the
REM discharges of motor neurons that control large
muscles would awaken the sleeper were they not
inhibited. Nature, being frugal, did not develop an
unneeded inhibitory pathway to block eye movements.
The biological significance of eye movement activity
during REM probably lies elsewhere. Eye movement
density appears to be roughly proportional to the
within-sleep level of brain arousal. It could therefor
provide a valuable non-invasive index of that
important sleep variable (for details and some relevant
data see Feinberg et al., 1987).
A REM=dream isomorphism also predicts that
dream reports should be longer with longer periods of
time in REM. A relation between narrative length and
time in REM was reported by Dement and Kleitman in
their pioneering study (1957). However, this early
work did not mention control for time of night. Since
REM periods are longer as sleep progresses it is
probable that length of time in REM was confounded
by time of night. A recent study (Rosenlicht et al.,
1994) that included control for time of night did not
find that narrative length was proportional to time
spent in REM prior to the awakening. Mean total
word count (TWC - a measure of dream length) in
reports from awakenings after 10 minutes of REM
sleep was not longer than after 5 min. However, mean
TWC from REMP4 was almost twice that from
REMP2, indicating that prior sleep duration is a much
more potent determinant of narrative length than time
As it became evident that mental activity occurs
in NREM sleep, some argued that REM dreams were
qualitatively different because they were often more
bizarre and affect laden. However, REM reports are
usually longer than NREM reports. Therefore, when
comparing the incidence of "dreamlike" events (visual
images, discontinuities, etc.) in narratives from the
two states, the length of the report must be taken into
account. Antrobus (1983) demonstrated that when
length of dream report, as measured by TRC (total
recall count) is partialed out, the apparent qualitative
differences between REM and NREM reports
disappeared. A number of investigators including
Foulkes and Schmidt (1983), Fein et al. (1985),
Cavallero and Foulkes (1990), and Cavallero et al.
(1992) have also shown that when length of dream
report is controlled, there is little or no difference
between REM and NREM reports. Thus, if narratives
elicited by awakenings from REM have distinguishing
features, these have yet to be demonstrated
More recently, the mnemonic sources of dream
content have been the subject of a number of
interesting studies (Cavallero et al., 1990; Cavallero,
1987; Cipolli et al., 1988; Cicogna et al., 1986, 1991;
Foulkes, 1982; Antrobus, 1987; Ehrlichman et al.,
1985). Stage differences in dream recall appear more
closely related to level of mnemonic activation and to
access to memory traces than to any special dream
production mechanism unique to one stage of sleep
(Cicogna et al., 1986, 1991). Thus, Cipolli et. al.
(1988) found that thematic units from different stages
on the same night were more closely related than those
from the same sleep stage on different nights. When
Ss were asked to make associations to dream material,
Cavallero and his colleagues (1987) found that
mnemonic traces were similar for sleep onset and
REM dreams. Finally, dream sources, as well as
content, appear similar in REM and NREM mentation
(Cavallero et al., 1990). In general, these results
suggest that the same cognitive systems produce
mental activity irrespective of EEG sleep stage, as
Foulkes proposed in 1982. Moreover when Cicogna et
al. (1986) compared memory traces from day
dreaming and sleep onset dreaming, they found a
similarity suggesting that žcognitive processes
involved in the creation of original narrative sequences
may be similar in sleep and waking.
We must, at last, explicitly reject the notion, as
appealing as it may be, that REM sleep is the brain
correlate of the dream. Sleep researchers, including
physiologists, should move on to study the true
situation - messier, more complex, but no less
interesting. Testable alternative hypotheses to explain
some of the variance in sleep mentation already exist.
Of these, we believe that the simplest and most
plausible are those that propose a positive relation
between memory accessibility and brain "activation"
or the within-sleep arousal level.
Rejecting the false REM=dreaming
equivalence also can advance research on the purely
physiological level. If the wild activity in sensory and
motor neurons does not affect mentation, it suggests
that this state involves an žinternalÓ deafferentation
that prevents these discharges from affecting
consciousness (Feinberg and March, 1995). Thus, a
remarkable attribute of the REM state, and what may
be an essential clue to its function, is the existence of a
gross Pg. 11 psychophysiological mismatch rather than
congruence. However, to pursue this possibility
requires that we accept the falsification of the
One final imponderable must be acknowledged.
The discussion above is based on the assumption that
mental activity reported on waking is recall of
mentation that was ongoing during sleep. This
inference has never been proved, and it remains
possible that Goblot (cited originally by Calvin Hall,
1981) was correct 100 years ago: the dreams we
report on awakening may be constructed entirely
during the waking process itself. While we consider
the extreme version of this hypothesis unlikely, we do
believe that a considerable portion of the dream report
is constructed during and immediately after
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