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For many decades considered too obvious, or mysterious,
to be studied scientifically, the notion of human consciousness
and how it is generated is once again under the microscope, reported
a panel of experts convened for a Mar. 22 STEP Science for All
session on "Consciousness: How Does the Brain Create Mind?"
The scientists were not all of one mind (heck, the mind itself
might not be all of one mind), but a consensus emerged that, in
the words of philosopher Dr. Patricia Churchland, "It looks very
likely that what we consider mental phenomena is actually brain
phenomena.There is no mind-independent substance, just the physical
brain" that is responsible for consciousness. "It's not 100 percent
certain, but highly probable."
That probability is the fruit of broad surveys of neuroscientific
study, narrowly focused investigations of an emotion as simple
as fear, and on fascinating glimpses into minds damaged by stroke
or other brain injury.
|Dr. Patricia Churchland suggested that we are as naïve today
about the true nature of consciousness as the ancients — who thought that the same “element” that
consumed firewood also illuminated stars, comets and the northern lights — were about
Churchland, professor of philosophy at the University of California,
San Diego, proceeded on the assumption that "mind is what the brain
does," but cautioned that we are far from being able to assign
any particular conscious state to the firing of specific neurons.
Even so, she argued, "We won't have defined consciousness if all
we find are the cortical correlates of it."
Just as fundamental concepts such as temperature, proteins and
genes were only understood after years of theoretical fine-tuning — what
she called "the profile of discovery" — consciousness itself
might one day yield to scientific analysis. She used the metaphor
of fire, which in ancient times was thought to be the root of such
disparate phenomena as stars, comets, the northern lights, as well
as forest fires, to explain how a definition of consciousness might
We now know that fire is rapid oxidation, she observed, but it
has taken millennia to realize that only terrestrial fires depend
on oxidation, and that stars are fueled by fusion, comets are cold
iceballs lit by starlight, and that no flame ignites the northern
"I suspect that consciousness will go the way of fire," she said. "Neuroscience
is still very much in its nascent stages," and cannot yet approach
the major puzzles of consciousness, including information storage,
modularity, computation, integration, functional organization and
time management, she said.
Science's ability to ask good questions about the nature of consciousness
has itself been hampered in the past 40 years by a fashionable
arm of inquiry known as behaviorism, said Dr. Bernard Baars, a
research fellow at the Neurosciences Institute in San Diego. "Consciousness
has only been spoken of in euphemisms, as in the way Victorians
used to speak of sex." His approach, now more than 2 decades in
the making, has been to study consciousness as a variable — states
characterized, like gravity, by more and less of it. He has pioneered
the concept of "global workspace theory." It posits that the brain — with
its 20 billion neurons each firing 10 times per second — is
like a "massive society of information processors." Consciousness,
in Baars' view, involves brainwide distribution of information;
unconscious input stays, by contrast, quite limited in distribution.
|Speakers at the STEP forum on human consciousness
included (from l) Dr. Todd Feinberg, Dr. Joe LeDoux, Churchland and Dr. Bernard Baars.
Like Churchland, he agrees that it is "too early in the field's
history" to arrive at a conceptual definition of consciousness.
But just as with fire, and temperature and genes, some fairly smart
operational definitions are maturing toward actual concepts.
Interestingly, Baars argued that dreaming is actually a conscious
state — studies have shown it (and common sense suggests
that humans would have no record of having dreamed if not for this
Lest the discussion become too abstract, Dr. Joe LeDoux of the
Center for Neural Science at New York University illuminated the
basic neural pathways underlying consciousness of a very raw kind — the
sense of fear. Examining the nature of feelings and how the brain
makes them, he showed that our emotional responses aren't necessarily
dependent on feelings. There are unconscious pre-processes that
generate conscious feelings.
If you see a snake, for example, you unconsciously recoil, and
only later form an emotion.
LeDoux advanced a "reconsolidation" theory of memory in which
our recollections are only as good as the last time they were retrieved;
we have no access to the virgin events that originally created
them. Perhaps that explains why people habitually revisit bad memories;
repeated rinsing might dilute their unpleasantness.
Commenting on the role of the unconscious, LeDoux noted, "There's
more to the self than meets the mind's eye."
If consciousness can be defined as self-awareness, what better
way to study it than to look at how it changes when damaged by
head injury, or stroke or aneurysm? Dr. Todd Feinberg of Albert
Einstein College of Medicine offered a clinician's view of the
impact of neurological disorders on sense of self.
He focused on delusional mental syndromes in which victims don't
recognize their own body parts as belonging to them. In one, married
women who are afflicted commonly misidentify the limb as belonging
to their husband; men affected by it are likely to attribute ownership
to the mother-in-law, he insisted with a straight face.
These conditions, including Capgras syndrome, asomatognosia and
alien hand syndrome (in which, in its classical form, a person's
hand systematically tries to undo the actions of the other) yield
evidence for Feinberg of a "neural hierarchy theory" making consciousness
not the king atop a mountain of subservient neurological input,
but rather a democracy moved by forces erupting within it.
The four guest speakers might not fully have answered the question, "What
is the real nature of conscious awareness?," posed by the meeting's
lead organizer, NCI's Dr. Grace Ault, but they certainly reached
the borderlands. To see the whole program, visit www.videocast.nih.gov.