[Paleopsych] NYT Magazine: Jim Holt: Of Two Minds

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Jim Holt: Of Two Minds
New York Times Magazine, 5.5.8
http://www.nytimes.com/2005/05/08/magazine/08WWLN.html

    The human brain is mysterious -- and, in a way, that is a good thing.
    The less that is known about how the brain works, the more secure the
    zone of privacy that surrounds the self. But that zone seems to be
    shrinking. A couple of weeks ago, two scientists revealed that they
    had found a way to peer directly into your brain and tell what you are
    looking at, even when you yourself are not yet aware of what you have
    seen. So much for the comforting notion that each of us has privileged
    access to his own mind.

    Opportunities for observing the human mental circuitry in action have,
    until recent times, been almost nonexistent, mainly because of a lack
    of live volunteers willing to sacrifice their brains to science. To
    get clues on how the brain works, scientists had to wait for people to
    suffer sometimes gruesome accidents and then see how the ensuing brain
    damage affected their abilities and behavior. The results could be
    puzzling. Damage to the right frontal lobe, for example, sometimes led
    to a heightened interest in high cuisine, a condition dubbed gourmand
    syndrome. (One European political journalist, upon recovering from a
    stroke affecting this part of the brain, profited from the misfortune
    by becoming a food columnist.)

    Today scientists are able to get some idea of what's going on in the
    mind by using brain scanners. Brain-scanning is cruder than it sounds.
    A technology called functional magnetic resonance imaging can reveal
    which part of your brain is most active when you're solving a
    mathematical puzzle, say, or memorizing a list of words. The scanner
    doesn't actually pick up the pattern of electrical activity in the
    brain; it just shows where the blood is flowing. (Active neurons
    demand more oxygen and hence more blood.)

    In the current issue of Nature Neuroscience, however, Frank Tong, a
    cognitive neuroscientist at Vanderbilt University, and Yukiyasu
    Kamitani, a researcher in Japan, announced that they had discovered a
    way of tweaking the brain-scanning technique to get a richer picture
    of the brain's activity. Now it is possible to infer what tiny groups
    of neurons are up to, not just larger areas of the brain. The
    implications are a little astonishing. Using the scanner, Tong could
    tell which of two visual patterns his subjects were focusing on -- in
    effect, reading their minds. In an experiment carried out by another
    research team, the scanner detected visual information in the brains
    of subjects even though, owing to a trick of the experiment, they
    themselves were not aware of what they had seen.

    How will our image of ourselves change as the wrinkled lump of gray
    meat in our skull becomes increasingly transparent to such exploratory
    methods? One recent discovery to confront is that the human brain can
    readily change its structure -- a phenomenon scientists call
    neuroplasticity. A few years ago, brain scans of London cabbies showed
    that the detailed mental maps they had built up in the course of
    navigating their city's complicated streets were apparent in their
    brains. Not only was the posterior hippocampus -- one area of the
    brain where spatial representations are stored -- larger in the
    drivers; the increase in size was proportional to the number of years
    they had been on the job.

    It may not come as a great surprise that interaction with the
    environment can alter our mental architecture. But there is also
    accumulating evidence that the brain can change autonomously, in
    response to its own internal signals. Last year, Tibetan Buddhist
    monks, with the encouragement of the Dalai Lama, submitted to
    functional magnetic resonance imaging as they practiced ''compassion
    meditation,'' which is aimed at achieving a mental state of pure
    loving kindness toward all beings. The brain scans showed only a
    slight effect in novice meditators. But for monks who had spent more
    than 10,000 hours in meditation, the differences in brain function
    were striking. Activity in the left prefrontal cortex, the locus of
    joy, overwhelmed activity in the right prefrontal cortex, the locus of
    anxiety. Activity was also heightened in the areas of the brain that
    direct planned motion, ''as if the monks' brains were itching to go to
    the aid of those in distress,'' Sharon Begley reported in The Wall
    Street Journal. All of which suggests, say the scientists who carried
    out the scans, that ''the resting state of the brain may be altered by
    long-term meditative practice.''

    But there could be revelations in store that will force us to revise
    our self-understanding in far more radical ways. We have already had a
    hint of this in the so-called split-brain phenomenon. The human brain
    has two hemispheres, right and left. Each hemisphere has its own
    perceptual, memory and control systems. For the most part, the left
    hemisphere is associated with the right side of the body, and vice
    versa. The left hemisphere usually controls speech. Connecting the
    hemispheres is a cable of nerve fibers called the corpus callosum.

    Patients with severe epilepsy sometimes used to undergo an operation
    in which the corpus callosum was severed. (The idea was to keep a
    seizure from spreading from one side of the brain to the other.) After
    the operation, the two hemispheres of the brain could no longer
    directly communicate. Such patients typically resumed their normal
    lives without seeming to be any different. But under careful
    observation, they exhibited some very peculiar behavior. When, for
    example, the word ''hat'' was flashed to the left half of the visual
    field -- and hence to the right (speechless) side of the brain -- the
    left hand would pick out a hat from a group of concealed objects, even
    as the patient insisted that he had seen no word. If a picture of a
    naked woman was flashed to the left visual field of a male patient, he
    would smile, or maybe blush, without being able to say what he was
    reacting to -- although he might make a comment like, ''That's some
    machine you've got there.'' In another case, a female patient's right
    hemisphere was flashed a scene of one person throwing another into a
    fire. ''I don't know why, but I feel kind of scared,'' she told the
    researcher. ''I don't like this room, or maybe it's you getting me
    nervous.'' The left side of her brain, noticing the negative emotional
    reaction issuing from the right side, was making a guess about its
    cause, much the way one person might make a guess about the emotions
    of another.

    Each side of the brain seemed to have its own awareness, as if there
    were two selves occupying the same head. (One patient's left hand
    seemed somewhat hostile to the patient's wife, suggesting that the
    right hemisphere was not fond of her.) Ordinarily, the two selves got
    along admirably, falling asleep and waking up at the same time and
    successfully performing activities that required bilateral
    coordination, like swimming and playing the piano. Nevertheless, as
    laboratory tests showed, they lived in ever so slightly different
    sensory worlds. And even though both understood language, one
    monopolized speech, while the other was mute. That's why the patient
    seemed normal to family and friends.

    Pondering such split-brain cases, some scientists and philosophers
    have raised a disquieting possibility: perhaps each of us really
    consists of two minds running in harness. In an intact brain, of
    course, the corpus callosum acts as a constant two-way
    internal-communications channel between the two hemispheres. So our
    everyday behavior does not betray the existence of two independent
    streams of consciousness flowing along within our skulls. It may be,
    the philosopher Thomas Nagel has written, that ''the ordinary, simple
    idea of a single person will come to seem quaint some day, when the
    complexities of the human control system become clearer and we become
    less certain that there is anything very important that we are one
    of.''

    It is sobering to reflect how ignorant humans have been about the
    workings of their own brains for most of our history. Aristotle, after
    all, thought the point of the brain was to cool the blood. The more
    that breakthroughs like the recent one in brain-scanning open up the
    mind to scientific scrutiny, the more we may be pressed to give up
    comforting metaphysical ideas like interiority, subjectivity and the
    soul. Let's enjoy them while we can.

    Jim Holt is a frequent contributor to the magazine.