Hobson and McCarley attacked three key as-
pects of Freudian dream theory. First, they in-
sisted that dreaming is a normal function of the
sleeping brain, occurring every 90 minutes as the
brain cycles in and out of REM sleep, and not
an offshoot of neurosis. Second, they argued
that dreams are instigated by random activations
of the brain stem during REM sleep, not by a
need to suppress unacceptable thoughts and de-
sires. Third, they contended that the bizarre fea-
tures of dreams are not due to any intentional
obfuscation of some harbored illicitness; in-
stead, “the forebrain may be making the best of
a bad job in producing even partially coherent
dream imagery from the relatively noisy signals
sent up to it from the brain stem.”
Hobson and McCarley also
stressed that their model “does not
deny meaning to dreams … nor
does it imply that they are without
psychological meaning or func-
tion.” Rather, psychological pur-
pose derives from the synthesis por-
tion of Activation-Synthesis. There-
fore, in a comment particularly rel-
evant today, “dreaming sleep may
… provide a biological model for
the study of memory, [with] a func-
tional role for dreaming sleep in
promoting some aspect of the
Surprisingly, however, their evi-
dence was circumstantial at best. The
trailblazers based it on what they
called “brain-mind isomorphisms”
— similarities between psychological
and physiological aspects of dream-
ing — an approach they credited to
Freud. Hobson and McCarley sug-
gest, then, that dreams of flying, for
instance, ensue from the internal ac-
tivation of the vestibular system during REM
sleep. Like Kipling’s Just So Stories, the logic
makes sense, but the science leaves many gaps.
Nonetheless, the Activation-Synthesis model
took off. In fact, the prestigious American Journal
of Psychiatry published Hobson and McCarley’s
explication as a lead article. And Hobson, with
whom I studied, later wrote extensively about
the model, extolling the neurophysiological
basis of dreaming, but focusing almost exclusively on activation. Consequently, mental
health practitioners, authors of psychology and
psychiatry textbooks, and their students came to
believe Activation-Synthesis demonstrated that
dreams were meaningless, functionless epiphe-nomena of the sleeping brain. This brave, new
model of dreaming has largely replaced Freudian theory both in college psychology courses
and among clinicians and researchers, even as
Freudian dream interpretation remains an essential motif in popular culture and the arts.
off-line processing of memories, not only stabilizing and strengthening them, but also extracting their meaning, as Matthew Walker, principal
investigator at the Sleep and Neuroimaging Laboratory in the Department of Psychology at
University of California, Berkeley, and I reviewed in a paper published earlier this year in
Nature Neuroscience. And in 2010 research, my
Harvard colleague Erin Wamsley and I charted
a strong correlation between dreaming about a
recently learned skill and subsequent improvement in its performance. Examining both nocturnal dreams and waking daydreams, we have
repeated these findings, and, thus, propose that
“far from being a random or meaningless distraction, spontaneous cognition during states of
sleep and resting wakefulness appears to serve
Actually, this idea of a link between sleep and
memory processing is nothing new. The ancient
Roman rhetorician and educator Quintilian
Important refinement
Recent advances in cognitive neuroscience re-
inforce Activation-Synthesis but shift the focus
from the randomness of activation to the mean-
ingfulness of synthesis. Sleep plays a part in the
important functions related to processing past
memories and planning for the future.”
What we did in these experiments was quite
simple. In the morning, students navigated a
virtual 3-D maze in a computer game. We then
tested how long it took them to get out of the
maze from various points. That afternoon, half
the subjects napped for 90 minutes while the
other half watched rather boring videos.
Around 5 p.m., we retested everyone. As we
had expected (or at least hoped!), those who
napped got through the maze about one minute
faster than they had before but those who had
stayed awake took about one minute longer. We
also woke up the napping subjects twice to col-
lect their dream reports. Only those who report-
ed dreaming about the maze wound up faster at
the 5 p.m. test. We also asked those who had to
stay awake what had been on their minds at
those same two junctures; whether they report-
ed thinking about the task or not, they showed
no improvement at the 5 p.m. test. Just 33 years
after Hobson and McCarley’s speculation, firm
scientific evidence confirms that, for at least
this one memory task, sleep enhances subjects’
memories of what they recently learned, but
only if they dream about it!
noted in the first century A.D.,
“Things which could not be recalled on the spot are easily coordinated the next day.” In modern
times, the scientific study of sleep
and memory only began in 1972,
with the pioneering work of psychologist and academic Carlyle
Smith. And it was only around the
year 2000 that the field began in
earnest. Since then, understanding
of this link between sleep and
memory processing has grown exponentially. Here are some
examples.
Sleep consolidates and enhances
memories. Most researchers believe
that sleep reactivates memories,
stabilizing and strengthening them
unconsciously. For procedural memories —
how to do things like ride a bicycle — subjects
perform better after a night’s sleep than at the
end of instruction or after a period of daytime
wakefulness. In 2002, colleagues and I trained
people on a finger-tapping task, typing the se-
quence 4-1-3-2-4 over and over during 12 half-
minute trials. After training them in the morn-
ing, we tested them 10 minutes after the last
trial and 10 hours later, and they revealed no
further improvement. But when we instead
trained them in the evening and tested them the
next morning after a night’s sleep, they were
10 percent to 20 percent faster and made fewer
mistakes. In other cases, for example verbal
memory, sleep slows the rate of forgetting and
makes memory more resistant to interference
from newly learned material. In a 2006 study,
we taught subjects a list of word pairs like
“horse-track.” They did somewhat better re-
taining the pairs when tested after a night of
sleep versus after a day of wakefulness. Other
subjects were additionally taught a list of com-
peting word pairs like “horse-hay” before re-
testing. The new list made remembering the
original pairs much harder after the day of
wakefulness, but not after the night of sleep.
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