L.A. TIMES / NEWS
/ FRONT PAGE / STORY
L.A. TIMES / NEWS
/ FRONT PAGE / STORY
Exotic devices that allow the
brain to be caught in the act of thinking let researchers explore science's
last frontier--the source of human consciousness.
By ROBERT LEE
HOTZ, Times Science Writer
I have something in mind--a thought so evanescent
that it comes and goes in milliseconds.
To capture it in the act, UCLA neuroscientist
Mark S. Cohen has trained on my brain a 22-ton experimental imaging device,
twice as powerful as--and 30,000 times faster than--any conventional medical
imager. This nuclear magnetic resonance (NMR) imager generates a magnetic
field so forceful that, as it pulses and flexes around my head, the room
shakes with a 100-decibel pile-driver roar.
Every 50 milliseconds, it captures an image
of the physical spark of my imagination at work--and something more.
Only part of my conscious mind attends to
the mental exercise that Cohen is recording. The rest is abuzz--worried
whether I can perform the task properly, curious about how well my mind
will photograph, and wondering most of all about the motives of these scientists
who are so intent on the neurobiology of my thoughts.
This irrepressible mental chorus constitutes
the background noise in the NMR image Cohen takes of my brain. It is also
the core of the most perplexing problem in science: What is consciousness?
The human brain, and the self-awareness
that arises from it, is a mystery wrapped in an enigma, swaddled in a tough,
protective membrane and sealed inside the skull, unknowable until now except
by the most indirect means.
Until recently, only a surgeon ever saw
an exposed, living brain. A neuroscientist could learn more about its intangible
mental functions by reading poetry or arguing philosophy than by examining
the dead organ on an autopsy table.
Today, scientists have at hand an array
of exotic devices that can peer through the skull to catch the living brain
at work. Researchers at UCLA and other centers are using them to explore
one of the last uncharted territories: the structure and cognitive functions
of the human brain.
Emboldened by their ability to capture the
image of something as intangible as imagination, a growing number of scientists
are trying to study the one thing that many believe cannot be labeled,
scrutinized or even defined--human consciousness.
The effort to understand human consciousness
is an inquiry older than science itself. It is at the heart of a riddle
of identity that has preoccupied philosophers, mystics and theologians
for as long as there have been words to frame the query: Who--or what--am
I?
Many neuroscientists hope that by studying
the neurons of the brain, its genes, sensory perceptions, memory and language
systems, they may be able to collect enough information about the way it
works to finally discover the organizing principles underpinning all subjective
experience.
Consequently, researchers for the first
time feel confident enough to frame serious questions about the physical
foundations of the human spirit.
How do the physical processes of the brain
give rise to subjective experience?
Somehow, the fragile synapses and cells
of the human nervous system can perceive the world around them, learn from
their perceptions, reinforce memories with the force of emotion, plan ahead,
decide and act on incomplete information, as well as sleep, dream, wake
and pay attention.
The brain captures its moods in melodies.
It invents stock markets, founds religions and orbits telescopes. It is
introspective enough to develop psychoanalysis.
"There is something very mysterious
about consciousness," said Christoff Koch, a theoretical neurobiologist
at Caltech. "Why can objective physical systems have subjective states?
It is baffling.
"It gets at the central idea of the
soul."
For the human brain, the scientific investigation
of consciousness is the beginning of an unusual journey of self-discovery.
"We are trying to understand who we
are by studying the organ that allows you to understand who you are,"
said Antonio Damasio, an expert at the University of Iowa on the brain,
cognition and behavior.
"Consciousness," said David Chalmers,
a cognitive scientist and philosopher at UC Santa Cruz, "is the last
frontier of science."
Chemistry and Electricity
Unraveling the nature of consciousness,
however, is a problem too daunting for any one scientist to address in
its entirety.
Instead, researchers are teasing apart isolated
neural processes, such as how the brain perceives color or how neural cells
focus attention, in the hope that they can gather evidence of how a conscious
mind is assembled from different brain processes.
On scores of university campuses, scientists
trace the ebb and flow of chemicals that trigger brain functions, the blood
flows that nourish them and the electrical patterns they generate. They
are trying to catch the mind in the act of being.
*
As they pull together new insights into
how the brain functions, a growing number of neuroscientists believe that
the mental processes underlying consciousness arise from an intricate madrigal
of two languages--chemistry and electricity--communicated through networks
of millions of neurons, all orchestrated precisely in time.
"We are the activity of the neuronal
machine," said Rudolfo Llinas, an expert at New York University on
the brain and cognition.
For the first time, researchers are identifying
the connections between the brain's physical anatomy and the mechanisms
of perception, learning and other, higher cognitive functions.
Investigators are beginning to understand
how experiences can lodge permanently among millions of scattered neurons--to
be revived in milliseconds by the smell of a baking pastry, a familiar
melody or a photograph.
Memory is more complicated than anyone had
imagined. Researchers such as Larry Squire at UC San Diego have discovered
that the brain harbors many independent systems of memory, while Erin Schumann
at Caltech and her colleagues are revising ideas of how knowledge is retained
in the chemistry of nerve cells.
Scientists have determined that the brain
handles memories of events and emotions differently than memories of ingrained
habits and tasks.
Short-term memories are fundamentally different
from long-term memories and may be forged in entirely different ways. False
memories appear to be handled differently in the brain than memories based
on true events, brain scans suggest.
Memory's unexpectedly intricate arrangements
mirror those of other neural systems involved in the operations of a conscious
mind.
Until recently, most scientists believed
that language was handled by the left side of the brain. But the mechanisms
of language are much more decentralized than previously thought. And the
way the growing brain handles language is much more flexible than previously
believed, research by Elizabeth Bates at UC San Diego suggests.
Names of animals and names of tools are
handled by largely separate brain regions, other scientists discovered.
Knowledge of the concepts they describe is stored in another discrete system.
*
The words, syntax and concepts of a person's
native tongue are stored so separately from any language learned later
in life that a stroke can knock out the ability to speak one but not the
other.
By highlighting nuances of brain functions,
sophisticated biomedical sensors offer glimpses of tantalizing relationships
between physical brain structures and conscious mental activity:
* Subtle differences in brain anatomy appear
to affect the ways men and women process information, even when thinking
about the same things, hearing the same words or solving similar problems.
* The most efficient brains appear also
to be the smartest, with the brains of those with the highest IQs using
the least energy. Learning and practice appear to improve the brain's efficiency.
* Small structural abnormalities appear
to develop in the brains of people with Alzheimer's disease or Huntington's
chorea long before any noticeable behavioral symptoms can be diagnosed.
* Minor alterations in neural circuits for
vision and hearing may be responsible for dyslexia, while brain abnormalities
in regions involved in inhibiting mental activity could be the cause of
attention deficit hyperactivity disorder, which affects about 5% of school-age
children.
But the search for clues to consciousness
leads down stranger alleys.
From nature's own experiments--the victims
of disease and brain injury--neurologists are obtaining glimpses into the
workings of the conscious mind by seeing how defects twist its usual attributes.
*
What is one to make of an otherwise normal
man--a victim of a rare mental disorder called Charles Bonnet syndrome--who
occasionally sees leprechauns, the amputee who thinks he is holding a cup
in the hand he no longer has, or the engineer who sees Technicolor cartoon
characters cavorting in a blind spot in her visual field.
Stranger still are victims of a mental disorder
called associative agnosia, who easily can draw any object but cannot recognize
what it is, or those with "blindsight," whose sense of sight
functions normally but who cannot make themselves consciously aware of
what their eyes see.
Why should brain damage leave one woman
unable to name animals, but able to name any other object?
From these and dozens of other hints, researchers
today are identifying the puzzle pieces of the brain, yet they are far
from understanding how they fit together into the cohesive whole of the
human mind.
"Why does all this processing give
you an inner life?" asked UC Santa Cruz's Chalmers. "Why is it
that these processes should give rise to the consciousness in the first
place?"
Our Uniquely Human Self-Consciousness
Some researchers argue that consciousness
in some form may extend beyond humans to other species.
Each human mind may be unique, but all its
higher cognitive functions take place in a brain closely resembling those
of more primitive primates such as apes and chimpanzees, say experts in
neural evolution.
The human brain appears to have no unique
cells, chemicals, neural circuits or major anatomical structures, experts
said. All the known differences are a matter of degree.
Other species can plan ahead based on experience,
combining sensory stimuli, attention and short-term memory. Nor is the
human mind unique in its ability to form concepts, some researchers contend.
Even pigeons appear to be able to sort objects into categories and recognize
abstract relationships.
What seems to distinguish human consciousness
is its subjective self-awareness--the feeling of being "me."
And that is where most scientists throw
up their hands in frustration, because human self-awareness is itself the
best, and perhaps only, evidence of its existence: I know I have a mind
because I have a mind that is aware of itself.
"How do you explain this quantum leap
in control over the mind in humans, with basically the same machinery you
have in monkeys?" asked neurobiologist Martin C. Sereno at UC San
Diego. "People just have more control over what is going on in their
heads--for better or worse."
*
There is no shortage of new theories from
scientists and philosophers trying to account for the novelty of human
consciousness.
Some contend that consciousness is the byproduct
of a Darwinian tooth-and-claw competition between mental states trying
to dominate behavior.
On the other hand, Oxford University mathematician
Roger Penrose proposed that consciousness must be a property of abstruse
particle physics operating inside brain cells. Free will, he contends,
must arise from the random character of quantum mechanics--a rolling of
the subatomic dice.
Some experts in artificial intelligence
conclude that consciousness is nothing more than sophisticated computer-like
information processing. Special mental switching areas integrate all the
brain's perceptions into a sense of self, they suggest.
Indeed, if the raw meat of the human brain
can develop consciousness, they speculate, why can't the silicon of integrated
computer circuits?
Neuroscientists like Sereno and philosophers
like Daniel Dennett at Tufts University believe that language is one essential
prerequisite for the development of higher consciousness. How, after all,
can a brain be self-aware if it cannot talk to itself?
Damasio thinks they have it backward. In
his view, language developed well after the onset of awareness. The brain
harbored a sense of self long before it had a word to name it, he said.
"If you look at a chimpanzee, I have
no doubt it has a sense of self, just not as rich as yours or mine,"
he said. "What we have is enriched by a spectacular memory of our
past and by a memory of the plans of our future, combined with the fact
that we automatically translate whatever we think into language.
"That is truly, uniquely human."
However intoxicating the theoretical possibilities,
Nobel laureate Francis Crick at the Salk Institute in La Jolla insists
on keeping his ideas about consciousness tied as closely as possible to
what can be measured in a laboratory.
"There was too much talk and not enough
experiments, from my point of view," he said. "You really want
new experimental data and to not get into too many highfalutin arguments
about the nature of consciousness."
*
In Crick's view, the sweeping question of
human consciousness is too large to study. Instead he has teased off a
more manageable piece of the problem.
With his collaborator Christoff Koch, Crick
is looking for the neural mechanisms underlying visual awareness.
They are considering the role played by
special neural cells in the higher visual cortex. Some cells respond to
straight lines while other cells react to color, movement or even faces.
To assemble a coherent image, rich with all the sensory impressions, memories,
knowledge and emotions it conjures, these separate visual cells must somehow
link up to all the other neurons that relate to what the eyes are seeing.
At the highest levels of this process, Koch
and Crick believe, some cells must respond to the unified perception assembled
from so many other active brain cells. It is those special cells, they
speculate, that make someone "conscious" of what the brain has
perceived.
"People think consciousness must arise
from the incredible complexity of millions of interconnected neurons,"
Koch said.
"We don't think it is pushing the envelope
to say there are specific neurons that give rise to consciousness."
Theater of the Mind
The scanner has finished imaging my brain.
My head, still enveloped in an imaging cradle,
slides out of the massive machine like a spent artillery shell.
The experiment was deceptively simple.
I had been asked to tap the fingers of my
right hand together slowly, then quickly, then more slowly again. Then
I was asked to imagine doing the same tasks.
The machine recorded my brain functions
by tracking minute variations in the scanner's magnetic field caused by
alterations in neural blood flow.
It takes Cohen, who helped design the scanner,
hours on a high-speed computer to transform those thousands of individual
measurements into a picture of the brain that a human eye can comprehend.
Projected on a color monitor, the scans
yield rows of wrinkled raisin-shaped images of my brain. Daubs of bright
color highlight the regions that became active when I physically moved
my fingers and those regions that became active when I imagined the same
action.
Both tasks--real and imagined--lighted up
the same areas of the brain responsible for movement.
At some fundamental level, thinking about
an action and performing it appear to be almost the same.
"To me that is a fascinating response,"
said Cohen. It runs "counter to everything I was expecting."
The images his machine creates appear to
draw a direct connection between the inner life of the mind and the physical
mechanisms of the brain.
"In a sense, this kind of functional
imager . . . allows me to study covert mental activity--in essence, thought,"
he said.
Other recent imaging studies of brain function
reinforce the relationship between conscious mental states and the physical
structures of the brain:
* When mental patients hallucinate and hear
imaginary voices, those portions of their brain responsible for hearing
respond as if the voices were real.
* When people are asked to picture a map
of the United States in their mind, their brains respond as if they were
looking at an actual map, activating that part of the cortex responsible
for vision.
* When people are asked to picture an object
and then rotate it mentally, their brains act as if the object were turning
in front of them.
One surprising thing about these images
of perception is that they do not show where or how the mind's eye is focused
in the brain.
Subjectively, perceptions always appear
seamlessly, presented in the mind as an integrated whole. But these scans
showed no sign of an active anatomical area where sensory stimuli were
coordinated and collated.
So how is consciousness organized in the
physical structures of the brain?
To Cohen, the images suggest that consciousness
is itself the act of attention.
As the brain evolved, it must have developed
a way to focus itself selectively; otherwise, the constant burble of brain
activity and sensory perceptions would overwhelm it. In this theory, consciousness
may arise from the brain's need to concentrate, momentarily highlighting
some neural activities at the expense of others.
Consciousness therefore may not be continuous,
Llinas of New York University suggested.
It may flicker on and off as needed, like
a spotlight flashing in the darkened theater of the mind.
An Elusive Quarry
Some scientists contend that consciousness
emerges from the union of all the brain's physical properties, the way
a rainbow arises from the interplay of light, suspended water droplets
and air.
If that is the case, they argue, scientists
will never find the human mind no matter how hard they scrutinize the brain's
physical structure, any more than someone will find a rainbow in any one
of its scattered parts.
Indeed, Chalmers believes scientists will
discover eventually that human consciousness is an irreducible quality
of the universe, like space, mass or time.
"Instead of trying to explain consciousness
purely in terms of its physical processes, you should take it as a fundamental
entity in its own right," he said.
"We would like a unified theory of
consciousness in the same way that physicists are searching for a unified
theory of matter," he said.
*
Some worry that by reducing human consciousness
to its biological components, scientists will tarnish the worth of the
human spirit or undercut ideas of personal responsibility and free will.
But other researchers believe that a more detailed understanding of the
brain will only enhance individual self-respect by affirming the uniqueness
of each human mind.
"You will understand," said Nobel
laureate Gerald Edelman at the Neurosciences Institute in La Jolla, "why
your individuality is important."
*
In some ways, the search for the roots of
human consciousness stands much of traditional scholarly inquiry on its
head.
Scientists who, by temperament and training,
devote their lives to the collection of objective facts about the universe
around them are forced to grapple with the imponderables of the world within.
Researchers who are trained to exclude the
human element from experiments discover that the human element is the experiment.
Philosophers, more accustomed to purely
metaphysical speculation, are now expected to buttress their ideas with
hard data.
All of them feel caught up in a uniquely
human endeavor that--for better or worse--promises to alter forever humanity's
sense of itself.
* * *
THE BRAIN: A WORK IN PROGRESS
A growing number of scientists are trying
to study the one thing that many believe cannot be labeled, scrutinized
or defined--human consciousness.
THE SEARCH FOR UNDERSTANDING
'There is something very mysterious about
consciousness. Why can objective physical systems have subjective states?
It is baffling. It gets at the central idea of the soul.'
--Christoff Koch, a theoretical neurobiologist
at Caltech.
THE CHALLENGE
'We are trying to understand who we are
by studying the organ that allows you to understand who you are.'
--Antonio Damasio, an expert at the University
of Iowa on the brain, cognition and behavior
GLOSSARY
Cortex:
Where most high-level functions associated
with the mind are implemented. Some of its regions are highly specialized.
For example, the occipital lobes located near the rear of the brain are
associated with the visual system. The motor cortex helps coordinate all
voluntary muscle movements.
Cerebral hemispheres:
Symmetrical halves of the brain. There are
two occipital lobes, two parietal lobes and two frontal lobes. The two
hemisphere are in continual communication with each other. Each acts as
an independent parallel processor with complementary functions.
Left cerebral hemisphere:
Appears most closely associated with a conscious
self. The left hemisphere, which usually manages the right side of the
body, controls language and general cognitive functions. It dominates in
deciding what response to make.
Right cerebral hemisphere:
Controls the left half of the body. In most
people it manages nonverbal processes, such as attention, pattern recognition,
line orientation and the detection of complex auditory tones.
Frontal lobes:
Located behind the forehead. They are most
closely linked with making decisions and judgments.
Limbic system:
A number of interconnected brain structures
linked to hormones, drives, temperature control, emotion, and, in one part,
to memory formation. Neurons affecting heart rate and respiration appear
concentrated in the hypothalamus and direct most of the physiological changes
that accompany strong emotion.
Hippocampus:
Plays a crucial role in processing various
forms of information as part of long-term memory. Damage to the hippocampus
will produce global retrograde amnesia, or the inability to lay down news
stores of information.
* * *
About This Series
Who are we? Where did we come from? While
many scientists search for clues to these ultimate questions by probing
the far reaches of the universe, others think the answers lie inside our
own heads. Their probes are uncovering galaxies of neural cells, each twinkling
with the brain's life forces. As it orchestrates human behavior, this symphony
of electrochemical communication may indeed constitute our very essence.
Sunday: The explosion of knowledge in the
field of brain development, where researchers are finding that those first
few years of life are far more critical than anyone had guessed.
Monday: New technology is uncovering the
brain's prominent role in emotions.
Tuesday: How brain researchers are overturning
traditional ideas about mental illness.
Today: Human consciousness.
Special Internet Site
Beginning today, a special section of The
Times' World Wide Webb will be devoted to information about the human brain.
The full text, photos and graphics from this four-part series will be available,
plus a wide range of additional information and graphics prepared especially
for the Internet. Point your Web browser to: http://www.latimes.com/thebrain
Copyright Los Angeles Times