Identifying
those pieces has led to an explosion of information about
how the brain is organized
—and knowing the organizational
plan is critical to understanding how any system works.
Traditionally, physiologists have prospered from the mantra
"form follows function." That is, natural selection
forces a structure to evolve toward the most efficient design
for its particular task. So by studying the design, we can
make good guesses about the task.
For instance,
if you'd never seen a typewriter before and wanted to
figure out how it worked, you'd only have to take it apart.
Likewise, draw a blueprint of the digestive tract and
you've come a long way toward understanding how the body
processes food. But take the brain apart and all you'll
get is a mosaic of gray and white tissue—anatomy
without obvious purpose. It's a black box instead of a
machine; a computer instead of a typewriter.
Like
a computer, the brain relies on electronic circuitry to
perform its job. It stores data in both short-term and
long-term memory. It rapidly sorts and processes information.
Like a computer, you can't tell what it does by taking
it apart; instead, you have to turn it on. But if it's
on, you can't take it apart. Catch 22.
Functional
MRI lets us look at what's happening inside the box while
it's turned on. With it, we can see exactly what regions
of the brain are activated when a specific task is performed,
effectively getting form from function. The black box
is growing transparent—and its design isn't what
we expected.
For
example, Kanwisher, who studies how we see things, has
demonstrated that one region of the visual cortex is activated
when a person is shown a picture of a place, but that
a completely different region of the cortex is activated
when a person is shown a picture of a face.
"Facial
recognition is separated from other things in the visual
system," she says. "We are extremely visual
organisms. Over a dozen specific regions have been found
in the visual cortex alone in the last few years, and
more are expected."
Why
would our brain use different neurons to recognize faces
versus recognizing a familiar building?
"We're
extremely social primates," Kanwisher says. "In
the evolution of our primate ancestors, it was probably
pretty important to survival to know who you were looking
at; whether someone was a friend or a foe. It's also possible
that facial recognition is simply very different from
every other visual task and needs a highly specialized
area. Or maybe we just look at faces so much more than
anything else that the brain has specialized itself."
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