My thinking about the question of consciousness started
early since the afternoon in Roger Sperry's lab at Caltech
almost 40 years ago when I tested the first split-brain
patient. Right off the bat it seemed that whatever consciousness
was, one could have two of them after the neurons which
connected the two cerebral hemispheres were surgically
separated. Mind left did not appear to know about mind
right, and vice versa. Those first impressions, while
factually enduring, left much to be desired as a sophisticated
perspective on the question of consciousness. My situation
echoed Tom Wolfe's admonition: practice writing for 20
years before you seek a publisher.
Classic split-brain work has highlighted how the left
and right brain each possesses its own particular functions.
The studies would lead one to believe that the brain is
a collection of modules. Thus, the left hemisphere is
specialized for not only language and speech, but also
for intelligent behavior. After human cerebral hemispheres
are disconnected, a patient's verbal IQ remains intact,
and his problem-solving capacity, as observed in hypothesis
formation tasks, remains unchanged for the left hemisphere.
The left hemisphere thus remains unchanged from its pre-surgical
capacity; yet the largely disconnected, same-size right
hemisphere becomes seriously impoverished in many cognitive
tasks. While the largely isolated right hemisphere remains
superior to the isolated left hemisphere in certain activities
such as recognizing upright faces, having better attentional
skills, and perhaps also expressing more emotions it is
poor at problem solving and numerous other mental activities.
Thus, the left has modules specialized for higher cognitive
function while the right has modules specialized for other
functions.
Visuo-spatial function, for example, is generally more
acute in the right hemisphere, but left-hemisphere integration
may be needed to perform higher-order tasks. The use of
tactile information to build spatial representations of
abstract shapes appears to be better developed in the
right hemisphere; however, tasks such as the Block Design
test from the WAIS, which are typically associated with
the right parietal lobe, appear to require integration
between the hemispheres in some patients. Furthermore,
even though the right hemisphere is better able to analyze
unfamiliar facial information than is the left hemisphere
and the left is better able to generate voluntary facial
expressions, both hemispheres are capable of facial expression
when spontaneous emotions are expressed.
The uniquely human skills we possess may well be produced
by minute and circumscribed neuronal networks sometimes
referred to as "modules." And yet our highly modularized
brain generates a feeling in all of us that we are integrated
and unified. How does that feeling come about, even though
we are a collection of specialized modules? The answer
appears to be that there is a specialized left hemisphere
system we have designated as the "interpreter," a device
that seeks explanations for why events occur. The advantage
of having such a system is obvious. By going beyond observing
contiguous events and asking why they happened, a brain
can cope with these same events more effectively, should
they happen again. Recent investigations of ours have
extended research on the properties of the interpreter
and how its presence influences other mental skills. There
are, for example, hemisphere-specific changes in the accuracy
of memory processes. The predilection of the left hemisphere
to interpret events has an impact on the accuracy of memory.
When subjects were presented with pictures that represented
common events (i.e., getting up in the morning or making
cookies) and then several hours later were asked to identify
whether pictures in another series appeared in the first,
both hemispheres were equally accurate in recognizing
the previously viewed pictures and rejecting the unrelated
ones. Only the right hemisphere, though, correctly rejected
pictures in the second set that were not previously viewed
but were related to pictures from the first. The left
hemisphere incorrectly "recalled" significantly more of
these pictures as having occurred in the first set, presumably
because they fit into the schema it had constructed regarding
the event. This finding is consistent with the view of
a left hemisphere "interpreter" that constructs theories
to assimilate perceived information into a comprehensible
whole. In doing so, however, the elaborative processing
has a deleterious effect on the accuracy of perceptual
recognition. This result has been extended to include
verbal material.
By emphasizing specialized circuits that arise from natural
selection, we see that the brain is not a unified neural
net that supports a general problem solving device. If
we accept this notion, we can concentrate on the possibility
that smaller, more manageable circuits produce awareness
of a species' capacities. Holding fast to the notion of
a unified neural net means we can understand human conscious
experience only by figuring out the interactions of billions
of neurons. That task is hopeless. My scheme is not.
The same split-brain research that exposed shocking differences
between the two hemispheres also revealed that the human
left hemisphere has the interpreter. The left brain interpreter's
job is to interpret our behavior and responses, whether
cognitive or emotional, to environmental challenges. The
interpreter constantly establishes a running narrative
of our actions, emotions, thoughts, and dreams. It is
the glue that keeps our story unified and creates our
sense of being a coherent, rational agent. It brings to
our bag of individual instincts the illusion that we are
something other than what we are. It builds our theories
about our own life, and these narratives of our past behavior
seep into our awareness.
The problem of consciousness, then, is tractable. We
do not have to find the code of one huge, interacting
neural network. Instead, we must find the common and perhaps
simple neural circuit(s) that enables vertebrates to be
aware of their species-specific capacities, and the problem
is solved. The same enabling circuit(s) in the rat is
most likely present in the human brain, and understanding
that point makes the problem scientifically tractable.
What makes us so grand is that the circuit has so much
more to work with in the human brain.
Our brains are automatic because physical tissue carries
out what we do. How could it be any other way? That means
they do it before our conceptual self knows about it.
But the conceptual self grows and grows and reaches proportions
that find the biologic fact that our brain does things
before we are consciosuly aware of them of interest but
not disheartening. The interpretation of things past has
liberated us from a sense of being tied to the demands
of the environment, and it has created the wonderful sense
that our self is in charge of our destiny. All of our
everyday success at reasoning through life's data convinces
us of our centrality. Because of that we can drive our
automatic brains to greater accomplishment and enjoyment
of life.
