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The Undiscovered Mind
http://www.biomednet.com/hmsbeagle/71/xcursion/essay
From The Undiscovered Mind: How the Human Brain Defies Replication,
Medication, and Explanation (pp. 28-32)
by John Horgan
© 1999 by John Horgan. Used with permission of The Free Press. Posted
February 4, 2000 · Issue 71
Editor's note: At the behest of the Society for Neuroscience, the 1990's
were designated by the U.S. Congress as the "Decade of the Brain." In The
Undiscovered Mind, John Horgan describes the reaction of neuroscientist
and Nobel laureate Torsten Wiesel to the concept of this timeframe - it
was "foolish." "We need at least a century, maybe even a millennium, to
comprehend the brain." And that could be a conservative estimate -
indeed, as Horgan notes, the science of the mind may never have an end.
Horgan explores the many facets of mind-science, including neuroscience,
Freudian analysis, behavioral genetics, evolutionary psychology, the
philosophy of consciousness, artificial intelligence, and more. He
describes the remarkable research being done in these fields, and talks
with the researchers themselves about their sometimes astonishing
results. But ultimately, Horgan finds in all this research what
philosophers call an "explanatory gap" - while many mental apparatus can
be elegantly described, the ultimate "how" of the mind remains as elusive
as ever. And then, as we see below, there's the small matter of emotions.
Getting in Touch with Emotions
Even if they unravel the mechanisms underlying working memory and other
cognitive functions, neuroscientists must face another problem: How does
emotion fit into the puzzle? Until recently many neuroscientists sought
to sidestep emotion in their experiments, treating it as an annoying
source of experimental noise and distortion rather than a fundamental
part of human nature. Neuroscientists have followed the lead of cognitive
scientists, who have tried to understand those information-processing
functions that can be most easily duplicated in computers, such as
vision, recollection, speech recognition, and reasoning.
By avoiding emotion, neuroscientists and cognitive scientists have
created a peculiarly one-dimensional picture of the mind, according to
Joseph LeDoux, a neuroscientist at New York University. Cognitive science
"is really a science of only a part of the mind, the part having to do
with thinking, reasoning, and intellect," LeDoux complained in his 1996
book, The Emotional Brain. "It leaves emotions out. And minds without
emotions are not really minds at all. They are souls on ice - cold,
lifeless creatures devoid of any desires, fears, sorrows, pains, or
pleasures."
LeDoux, himself a cool, controlled man with deep-set eyes and a carefully
trimmed beard, has demonstrated that at least one emotion, fear, can be
approached empirically. Unlike language or other cognitive functions
unique to humans, LeDoux pointed out, fear is a biological phenomenon
whose roots reach back far into the history of life. The neural circuitry
and processes that underlie fear have been highly conserved through
evolution; thus experiments on rats and other animals may reveal much
about humans. The amygdala, which is crucial to the fear response, is
found not only in humans and primates but also in rats.
"The fear system is very, very simple," LeDoux told me. "You've got a
stimulus that comes in through standard input channels, goes to the
amygdala and goes out through the output channels," he said. Early
studies of fear responses had produced confusing results because the
experiments were too complex. "Every time you change the experiment, you
change the way the brain accomplishes the task. So the key in figuring
out the fear system is to strip it down to a simpler model."
LeDoux has carried out experiments in which rats have been conditioned to
associate a certain sound, such as a musical tone, with an unpleasant
sensation, such as an electric shock. The initial response of rats and
many other animals to such a stimulus is to freeze, an appropriate tactic
for an animal threatened by a predator. The freeze response is an innate,
reflexive function. LeDoux and his colleagues showed that damage to a
minute structure within the amygdala, called the lateral nucleus,
prevented rats from learning to freeze in response to the tone preceding
an electric shock. The cognitive ability of the rats was unimpaired in
other respects.
LeDoux was trying to unravel the circuitry required for more complex
fear-related behavior, which is sometimes called instrumental learning.
For example, when a rat learns that freezing does not prevent him from
being shocked, he tries avoidance - moving to a different part of the
cage or climbing up its sides. At this point, the rat makes the
transition from being an emotional reactor to an actor, LeDoux said,
capable of making choices and trying different strategies.
Psychologists once believed that the subjective sensation of fear is the
first component of the fear response; increased heart rate, sweating, and
other physiological symptoms were thought to be triggered by the
subjective sensation. LeDoux contended that the opposite is probably
true; physiological symptoms occur first and then initiate the subjective
sensation of fear. In many cases, moreover, the fear response might never
generate a conscious sensation. Our conscious, subjective feelings "are
red herrings, detours, in the scientific study of emotions," LeDoux has
written.
LeDoux felt that too much attention had been paid to consciousness
lately. "It would surely get you the Nobel Prize if you figured it out,"
he told me, "but I don't think it would tell us what we need to know"
about the mind. Although consciousness is often equated with the mind,
most mental processes occur beneath the level of awareness, LeDoux
pointed out. Consciousness, moreover, is a relatively recent innovation
of evolution. "Basically the brain is unconscious. Somewhere in evolution
consciousness evolved as a module. It's connected up to some other parts
of the brain, but not the rest of it."
Explaining consciousness is not as important as understanding how the
brain draws on both genes and experience to create a self, a personal
identity, in each individual. "That to me is the big question: how our
brain makes us who we are. Explaining consciousness wouldn't explain
that." The key to this issue is understanding how both nature and nurture
affect the brain's wiring. "What's often overlooked is that nature and
nurture speak the same language, which is the synaptic language," LeDoux
said. Ultimately all influences on personality, genetic or experiential,
become manifest at the level of the connections between neurons.
LeDoux doubted whether any single theory would account for emotion. There
are many aspects of emotion, he noted. "There's an evolutionary
component, there's a cognitive component, a behavioral component. It's
just a question of what the balance in the particular situation is."
Cognitive theories tend to focus on conscious emotional processes;
evolutionary theories emphasize innate emotional responses; behavioral
theories stress the role of environmental conditioning. "In any
particular emotional episode, it's not a matter of which one is right but
which one explains which part of the episode." Moreover, each emotion
probably requires a separate explanation; the mechanisms underlying fear
are probably quite different from those underlying lust or hatred.
LeDoux summarized the research that he and others have done on emotion,
and particularly fear, in The Emotional Brain. He also cautiously
suggested that investigations of the neurobiology of fear might at some
point yield better treatments for human anxiety disorders. LeDoux
expected psychiatrists to dismiss his rat experiments as irrelevant to
their work. But to his surprise, psychiatrists responded to his book
enthusiastically - almost too enthusiastically, LeDoux suggested. "It's
been almost this uncritical acceptance," he explained. "'Yes, let's go!
This is the answer!' They seem so desperate. I don't think I have the
answers in my book. I just threw out some ideas."
Like Gerald Fischbach, Torsten Wiesel, and other leading neuroscientists,
LeDoux readily acknowledges the shortcomings of his field. He once
stated, "We have no idea how our brains make us who we are. There is as
yet no neuroscience of personality. We have little understanding of how
art and history are experienced by the brain. The meltdown of mental life
in psychosis is still a mystery. In short, we have yet to come up with a
theory that can pull all this together. We haven't yet had a Darwin,
Einstein or Newton."
Then LeDoux suggested that neuroscience might not need a unifying theory:
Maybe what we need most are lots of little theories. It would be great to
know how anxiety or depression works, even if we don't have a theory of
mental illness. And wouldn't it be wonderful to know how we experience a
wonderful piece of music (be it rock or Bach), even in the absence of a
theory of perception. And to understand fear or love in the absence of a
theory of emotion in general wouldn't be so bad either. The field of
neuroscience is in a position to make progress on these problems, even if
it doesn't come up with a theory of mind and brain.
John Horgan is a freelance writer and author of The End of Science, a
U.S. best-seller that has been translated into ten languages. His awards
include the Science Journalism Award of the American Association for the
Advancement of Science (1992 and 1994) and the National Association of
Science Writers Science-in-Society Award (1993).
©2000 BioMedNet Ltd. All rights reserved.
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