http://www.sciencenews.org/20010811/bob12.asp
Scientists hope to raise the neural curtain on sleep's virtual theater
Bruce Bower
After his father's death in 1896, Viennese neurologist Sigmund Freud made a
momentous career change. He decided to study the mind instead of the brain.
Freud began by probing his own mind. Intrigued by his conflicted feelings
toward his late father, the scientist analyzed his own dreams, slips of the
tongue, childhood memories, and episodes of forgetfulness.
Freud's efforts culminated in the 1900 publication of The Interpretation of
Dreams. In that book, he depicted dreams as symbolic stories in which
sleepers' unconscious sexual and aggressive desires play out in disguised
forms.
Later in his life, Freud acknowledged that dreams don't always gratify wishes.
For instance, he noted that some dreams represent attempts to master a past
traumatic experience. Yet the father of psychoanalysis always held that dreams
contain both surface events and subterranean themes of great personal
importance. For that reason, he wrote, "the interpretation of dreams is the
royal road to a knowledge of the unconscious activities of the mind."
Freud's theory of how dreams work has had a huge cultural impact over the past
century, even as it attracted intense criticism. Now, brain scientists-members
of the discipline that Freud left behind-have stepped to the forefront of this
passionate dream dispute.
One prominent group of scientists asserts that Freud profoundly misunderstood
dreams. In their view, the act of dreaming yields a guileless collage of
strange but heartfelt images that carry no hidden meanings.
These scientists say that dreaming occurs when a primitive structure called
the brain stem stirs up strong emotions, especially anxiety, elation, and
anger. At the same time, neural gateways to the external world shut down, as
do centers of memory and rational thought. The brain then creates bizarre,
internal visions that strongly resonate for the dreamer.
An opposing view corresponds in many ways to Freud's ideas. Its supporters
portray dreams as products of a complex frontal-brain system that seeks out
objects of intense interest or desire. When provoked during sleep, this brain
system depicts deep-seated goals in veiled ways so as not to rouse the
dreamer.
A third group of investigators regards the brain data as intriguing but
inconclusive. Dreams may serve any of a variety of functions, they argue.
Depending on the society, these uses include simulating potential threats,
grappling with personal and community problems, sparking artistic creativity,
and diagnosing and healing physical illnesses.
"It is striking that 100 years after Freud [published The Interpretation of
Dreams], there is absolutely no agreement as to the nature of, function of, or
brain mechanism underlying dreaming," says neuroscientist Robert Stickgold of
Harvard Medical School in Boston.
A broad consensus exists on one point, though. If neuroscientists hope to
understand the vexing relationship of brain and mind, they need to get a
handle on dreams.
Dreams as an afterthought
Freud's royal road to the unconscious looks like a scientific dead-end to
psychiatrist J. Allan Hobson. Neuroscientific evidence indicates that the
sleeping brain churns out dreams as an afterthought to its other duties, argue
Hobson, Stickgold, and Edward F. Pace-Schott, also of Harvard Medical School.
"Unconscious wishes play little or no part in dream instigation, dream emotion
is uncensored and undisguised, sleep is not protected by dreaming, and dream
interpretation has no scientific status," Hobson says.
Hobson's assault on Freudian dream theory began more than a decade ago. At
that time, he proposed that dreams result from random bursts of activity in a
brain stem area that regulates breathing and other basic bodily functions.
These brain stem blasts zip to the frontal brain during periods of rapid eye
movement (REM) sleep, when the entire brain becomes nearly as active as when a
person is awake.
Dreams most often occur during REM sleep. A slumbering individual enters REM
sleep about every 90 minutes.
Hobson's group published a revision of this theory in the December 2000
Behavioral and Brain Sciences. Their new approach grants that dreams harbor
emotional significance, but not in the way Freud posited.
Brain imaging and sleep-laboratory data clearly delineate among wakefulness,
REM sleep, and non-REM sleep, the Harvard scientists note.
Three essential processes during REM sleep make it the prime time for
dreaming, they say. First, brain stem activity surges and sets off responses
in emotional and visual parts of the brain. Second, brain regions that handle
sensations from the outside world, control movement, and carry out logical
analysis shut down. Third, brain stem cells pump out acetylcholine, a chemical
messenger that jacks up activity in emotional centers.
At the same time, two neurotransmitters essential for waking
activity-noradrenaline and serotonin-take a snooze.
The result, in Hobson's view: a vivid hallucination, informed by strong
emotions, that takes bizarre twists and turns. REM sleep's biological makeup
fosters the mistaken belief that one is awake while dreaming, saps the ability
to reflect on the weirdness of dreams as they occur, and makes it difficult to
recall dreams after waking up.
REM sleep conducts far more important business than dreaming, Hobson argues.
Its central functions may include supporting brain development, regulating
body temperature, fortifying the immune system, and fostering memories of
recently learned information. The last possibility evokes heated scientific
debate
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--J. R.
Useless hypotheses, etc.:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, and ego.
Everything that can happen has already happened, not just once,
but an infinite number of times, and will continue to do so forever.
(Everything that can happen = more than anyone can imagine.)
We won't move into a better future until we debunk religiosity, the most
regressive force now operating in society.
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