SPRING 2003 •
VOLUME 7, NUMBER 3
BY
ANNE KEYSER
Think famous explorers,
and names like Magellan, Columbus, and Lewis and Clark come to
mind. If Petya Radoeva '03 continues on the course she has set
at Mount Holyoke, her name may one day be listed among those of
great adventurers whose journeys have opened once-mysterious terrain.
With the help of Mount Holyoke psychologist Joseph Cohen, and
funding from the College's Howard Hughes Medical Institute Undergraduate
Summer Research and Cascade Mentoring Summer Research programs,
the neuroscience and behavior major is mapping territory as vast
and uncharted as any encountered by better-known explorers--the
human brain.
Radoeva has been fascinated by
the workings of the brain since her first year at Mount Holyoke, when she took
Introductory Seminar in Psychology: Brain/Mind, taught by Cohen, professor of
psychology and education. She is not alone. From late-Stone Age doctors who
perforated the skull to relieve distress, pain, and evil spirits, to nineteenth-century
phrenologists who judged intellect and personality by the shape of the head,
scientists have long been curious about matters cerebral. Since the 1800s, they
have made great progress in identifying the brain's different regions and the
tasks each area controls. Still, much remains unknown about the most complicated
organ of the body, including the focus of Radoeva's research--how the brain
controls vision.
One recent theory is that the brain
has two separate systems for vision, one (visuoperception) for describing and
recognizing objects and another (visuomotor) for interacting with them. The
idea comes partly from studies of patients who have lost particular functions
due to strokes, tumors, and other brain injuries, says Cohen. Some patients
are able to recognize objects but unable to reach for them appropriately, he
explains; they might grasp a toothbrush's bristles rather than its handle, for
example. Others have just the opposite problem. They cannot identify or describe
the objects they see, yet they are able to interact with them flawlessly. Even
people with uninjured brains can show this kind of "dissociation" between visual
perception and action, says Cohen. They may misestimate the size of an object
that has been distorted by an optical illusion but, in grasping for it, will
scale their grip just right.
Despite such evidence, the dual-vision
theory is not favored by all neuroscientists. In fact, it is a hotly debated
hypothesis with lots of room for new explorers. Enter Radoeva. "I love challenges,"
she explains. With guidance from Cohen and neuroscientist Paul Corballis, Radoeva
designed an experiment that uses objects distorted by illusions to gauge the
sophistication and interaction of the visuoperception and visuomotor systems
within each hemisphere of the brain. Would the illusions "trick" one system
more than the other, she wondered? Would one system be stronger on one side
of the brain than on the other?
Some of the most exciting answers
came last academic year and summer, when Radoeva studied at Dartmouth College's
Center for Cognitive Neuroscience. There, she worked with Corballis, who inspired
her to dedicate her life's work to brain-damaged patients and who gave her the
opportunity to test an extremely rare subject. The man was an epileptic whose
doctors had stopped his seizures years earlier by severing the bundle of nerves
connecting the brain's right and left hemispheres. In "JW" and other so-called
"split-brain" patients, seizures cannot travel from one hemisphere to the other,
nor can commands of the visuoperception or visuomotor systems. When Radoeva
presented test objects in JW's right visual field, asking him to estimate their
size and then grasp them, only his brain's left hemisphere could respond, unaided
by messages from the right side. Likewise, his right hemisphere operated independently
for test objects presented in his left visual field.
Based on her results thus far,
including experimental trials conducted during January Term with patients in
her native Bulgaria, Radoeva and her advisers believe that the visuomotor system
is more developed in the brain's left hemisphere, while the visuoperceptual
system is more developed in the right. She also contends that the two systems
are present and interacting with each other to a similar extent in both hemispheres.
But those findings could change as Radoeva continues to collect and interpret
data for a senior honors thesis on hemispheric differences in the brain. After
graduation, she hopes to continue her investigation by specializing in psychiatric
and neurological disorders in a joint M.D./Ph.D. program.
"Petya is an enterprising, inventive,
resourceful, and dedicated researcher. In many ways she acts like an advanced
graduate student or even a mature scientist," said Cohen, who believes that,
someday, research like hers could inform prognoses and rehabilitation for patients
with brain damage in particular visual areas.
Radoeva dreams of such applications
of her work. "I really want to help people, to bring them back to life," she
says of her drive to understand (and, someday, heal) the human brain. "Science
makes progress in little steps, and our findings could potentially be one of
them." |
