By better understanding the zombie within, neurobiologists hope to
By Scott LaFee
UNION-TRIBUNE UNION-TRIBUNE STAFF WRITER
March 24, 2004
For most people, the prototypical zombie is a Hollywood creation, a
walking dead guy oblivious to everything, utterly unresponsive to any
stimulus other than its insatiable hunger for human flesh.
Such zombies if they actually existed would be easy to identify:
slack jaws, hollow, empty eyes, a body in an advanced stage of
decomposition. Real-world zombies, though, are even easier to spot.
They look exactly like you, me and everybody else.
That's not to say, of course, that any of us actually suffers from
cannibalistic cravings. Rather, as humans indeed because we are
humans we often behave like zombies. That is, we tend to live beyond
the pale of consciousness.
Consciousness is one of the great and lingering mysteries of science.
Francis Crick, the Nobel laureate who co-discovered the structure of
DNA, calls it "the major unsolved problem in biology."
Crick, who has spent the last couple of decades at the Salk Institute
in La Jolla conducting brain research, believes that all of the
brain's behaviors, including consciousness, result from the brain's
physical processes. For more than a decade, he and colleagues like
Christof Koch, a neurobiologist at the California Institute of
Technology in Pasadena, have argued that human self-awareness is
essentially the consequence of countless neurons, sensory cells and
other physiological systems interacting with the environment to create
the intangible entity we know as our minds.
Everything we think, say and do, contend Crick and Koch, can be
explained biologically. It is their ambition to prove it, to find what
they call "the neuronal correlates of consciousness."
And that's where zombies come in.
Living on autopilot
People talk without thinking all of the time.
If you doubt it, think about this: When you're talking, do you
construct each sentence first in your mind, piecing the words
together? Or do you simply talk, the words tumbling out in proper
sequence and syntax?
For the most part, it's probably the latter. You don't think about
each word before you speak it. "Your brain," says Koch, "takes care of
that quite well without any conscious effort on your part."
Speaking is, in profound ways, a "nonconscious" behavior. It is a
mental operation not directly associated with conscious feelings,
sensations or memories. It just sort of happens, seemingly, on its own.
The same is true about much of life. Surprisingly big chunks of it,
Koch writes in his new book, "The Quest for Consciousness," happen
without us being consciously aware they are happening.
"We all do things every day, virtually every minute, that do not
involve conscious thought, from tying our shoes, to driving to work or
working out, to cooking dinner," said Koch. "These actions are
essentially routine, automatic. You do them without thinking and often
have no direct memory of them afterward."
Neurobiologists call these actions "zombie behaviors," activities that
occur without conscious input or self-examination. They have been a
subject of scholarly debate for more than a century, serious grist for
philosophers and psychologists like Friedrich Nietzsche and Sigmund
Freud. Increasingly, they are also the stuff of science.
Koch says neuroscience has accumulated credible evidence that the
brain is filled with specialized sensory-motor processes, what he
calls "zombie agents," that carry out these unthinking behaviors. He
says there is a plausible explanation for their existence: They allow
us to be us.
All zombie behaviors have at least a couple of things in common: They
happen fast. And they are, in some way, routine. Many of these
behaviors are akin to reflexes, such as blinking when your view is
suddenly obstructed, sneezing when something tickles your nose or
flinching at an unexpected noise.Other zombie behaviors are more
subtle, such as the constant stream of mental directions that keep
your body upright, balanced and mobile when walking, that allow you to
change your gait or step when weaving through a crowd.
These behaviors cannot easily be done if you consciously think about
them. It takes too much time, time that could be vital to survival or
put to better use. And so our brains, constantly awash in sensory
information, have evolved streamlined, one-way information pathways to
get necessary signals from the brain to the body almost
instantaneously, without the delaying clutter of conscious thought.
"One of the cardinal advantages of zombie agents is that their
specialized nature allows them to respond more rapidly than the
general purpose perceptual system," writes Koch. "You grab for that
pencil before you actually see it roll off the table, or you move your
hand away from the hot burner before you feel its heat."
This last point is important, Koch says, because it refutes the idea
that you jerk your hand away because you consciously feel pain. You
don't. The movement is a spinal reflex. It does not require the brain
For humans, the presence and activity of myriad zombie agents means
significant regions of the brain can be put to better use.
Specifically, the cortical regions involved in higher cognitive skills
learning, memory, vision, language are free to grapple with new
problems and situations, to plan ahead. Other animals mice and
monkeys, for example have been shown to possess some aspects of
these properties, but to a lesser degree. Humans have more cortex,
language, insight and a deeper, more reflective self-awareness.
"It's a reasonable idea," said Larry Squire, a neuroscientist at UCSD
and the San Diego VA Medical Center. "Animals have evolved lots of
very specific adaptations for survival. Honeybees, for example, do
this very elaborate dance to communicate where to find food. But they
can use this information in only two ways: They do the dance for
others, or they go find the food themselves. They can't do anything
else with it.
"Humans are different. We can apply specific information to many other
unrelated events or actions. We're flexible. This is consciousness."
By better understanding the biological basis of zombie behaviors,
researchers hope they will learn more about consciousness. But it is a
daunting task, if only because it's exceedingly difficult to always
differentiate between the two.
Some zombie behaviors, for example, can appear quite complex. When a
dog wags its tail or a baby smiles, both may be doing so
automatically, without conscious thought.
More confoundingly, consciousness readily intrudes into zombie
behaviors. Consider the act of tying your shoes. It's a mechanistic,
routine action that generally requires no active thought. But at any
moment while tying your shoes, you can suddenly become aware that,
well, you're tying your shoes.
Such moments happen constantly, throughout the waking day. Your brain
is working on cruise control. Suddenly, you realize your brain is
working on cruise control.
"In the intact brain, zombie behaviors are so tightly interwoven with
conscious ones that it is difficult to isolate them," says Koch. "Even
if the response was generated automatically, awareness may follow
within the blink of an eye."
For scientists, parsing the distinctions between nonconsciousness and
consciousness means studying humans. Current animals models are of
limited value because consciousness is a subjective experience. Only
humans can directly communicate what's going on in their minds.
Figuring out what a lab rat is feeling is difficult, though not
Some of the most productive research into zombie behaviors involves
studying people who suffer from specific, clinical diseases affecting
Visual agnosia, for example, is a relatively uncommon condition in
which a patient cannot identify an object visually, but knows
immediately what it is if they touch it or hear it (as when a set of
keys is jingled). The cause is believed to be linked to localized
brain damage affecting a specific perceptual ability.
Koch cites a particular case study that he says helps illustrate the
presence and function of zombie agents operating beyond the kin of
D.F. is a 34-year-old woman who suffered widespread and irreversible
brain damage from an episode of carbon monoxide poisoning. She
survived but could no longer recognize most objects by sight. She was
not blind. She could see colors, step easily over objects, catch a
tossed ball and sketch things from memory.
"But she can't tell whether a pencil held in front of her is
horizontal or vertical, whether she is looking at a square or a
triangle, and she is unable to copy simple drawings," writes Koch.
Though she can't see things in any meaningful way, D.F. can interact
with them with remarkable accuracy. In one experiment, she was asked
to insert a card into a slanted slot. She did so easily, her hand and
arm rotating automatically to orient the card to the slot. Even with
the lights turned out halfway through the action, she had no trouble
posting the card.
Yet D.F. couldn't see the orientation of the slot, couldn't talk about
it, couldn't consciously rotate her hand to match the slot's slant.
Clearly, her abilities were being governed by brain processes outside
conscious, visually based thought.
Such experiments, repeated in varying degrees with patients suffering
from blindsight (an unusual condition in which a patient with cortical
blindness may perceive peripheral movement without actually being able
to see anything there), epilepsy and sleep walking, all suggest that
the brain may be operating two physically distinct and separate
systems, like a parallel processor.
That is, neural activity in some parts of the brain governs zombie
behaviors while other brain regions handle sensory input that demands
Or, posits Koch, a single network in the brain may be functioning in
two distinct, simultaneous modes. Sensory data move through cortical
processing stages until they trigger a stereotyped, nonconscious
behavior. If the data are too ephemeral or weak, that's where they stop.
But if the data are stronger or more sustained, they linger and
resonate. Consciousness kicks in as feedback between neurons escalates.
At the moment, these remain only ideas of what is happening in the
brain. Technologies like functional magnetic resonance imaging, which
allow scientists to see what parts of a brain are working in real
time, may provide the tools to delve deeper and better, but Koch
concedes there's a long way to go.
We can think about consciousness, but we can't explain it.
If zombie agents competently handle most of life's demands, a larger
question looms: Why be conscious at all? What's the benefit?
The answer is decidedly incomplete, and largely speculative.
Consciousness is clearly a property of certain kinds of highly evolved
biological organs, but not all. Your intestinal walls, for example,
are lined by more than 100 million neurons, but Koch notes that you
don't have conscious access to its workings.
Consciousness presumably provides an organism with an edge over an
organism that is not conscious. That advantage, suggests Koch, is the
ability to take large amounts of information, rapidly boil it down to
essential facts and then do something with the knowledge. A snarling
lion prompts a deer to run away; the same thing may inspire a human to
go make a spear.
Consciousness performs a sort of executive summary function, said Koch.
"A single, compact representation of what is out there is presented,
for a sufficient time, to the parts of the brain that can choose among
different plans of action. This is what conscious perception is about."
Awareness occurs, Koch said, at the interface between sensory
processing and mental planning.
It's a slippery concept, hard to grasp. But then, that's the nature of
the zombie within. Actions like learning how to dance, ride a bike or
climb a mountain can all become zombie behaviors through repetition.
Once mastered, it's harder to play the piano while thinking about
specific keystrokes than it is to simply let the fingers tinkle.
But such a talent begins with conscious thought.