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Mapping the Brain's Terrrain: Petya Radoeva '03 Explores Vision

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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."

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