What Is Split Brain Research?

Split-brain research in the mid-20th century opened up a whole new science. Scientists started mapping the brain once they saw how epileptics--who had undergone surgery to split the halves of their brains--functioned. The research eventually showed how amazing the brain is at adapting to such radical changes.

History

• In an attempt to relieve the suffering of people who had frequent grand mal seizures when medication proved ineffective, William Van Wagenen developed a radical surgical treatment. In 1940, working as a neurosurgeon in Rochester, N.Y., Van Wagenen cut the major band of nerve tissue connecting the left and right hemispheres of the brain. When partially or completely severed, the band, called the corpus callosum, appeared to cause epileptic seizures to cease in about 50 to 70 percent of epileptics.

  In the early 1960s at the California Institute of Technology, Nobel Prize-winning researcher Roger Sperry started working with a man who had undergone a corpus callostomy (had his corpus callosum severed to prevent seizures). It took the man a month to recover his ability to speak, but even after that, the man had persistent difficulty in reading or describing things on his left. Sperry's research went on to study the effects of corpus callostomy in animals, which was later continued by his assistant, Michael Gazzaniga, who became known as the "father of cognitive neuroscience" for his work in mapping areas of specialization in the brain.

Effects in Monkeys

• In experiments with monkeys, Gazzaniga showed that, in most respects, after the operation monkeys behaved and were treated normally. When presented with two buttons with different symbols on them, the monkey had no problem when it saw the buttons with its right eye and pushed the correct one to receive food. When the buttons were viewed with its left eye, the monkey could no longer distinguish between the two buttons and got confused and agitated.

Effects in Humans

• In experiments with humans, he found that vocal expression usually resided in the left hemisphere, while shape and pattern recognition resided in the right hemisphere. A man with a severed corpus callosum could verbally describe words and images presented to his right visual field. However, the man claimed that he could not see those presented to his left visual field, although with his eyes closed, he could draw a picture of the object or word he had seen with his left eye. Gazzaniga also presented similar subjects with blocks that had different designs on each face and asked them to assemble the blocks to match a picture. The left hand could easily and quickly arrange the blocks to match the picture. The right hand was completely unable to assemble the blocks correctly. Using both hands together, the hands of the subjects seemed to fight over how the blocks should be assembled.

Theories

• Although the two halves of the brain seem to have particular specialties that have difficulty coordinating when the corpus callosum is severed or damaged, there is evidence that over time, the brain finds other ways to connect the two hemispheres. In many corpus callostomy patients, only the first two-thirds of the corpus callosum are severed, leaving the rear third, called the splenium, intact. Patients eventually learn to give verbal control to the hemisphere that has the pertinent sensory information, even if that is the right hemisphere. Researchers theorize that the splenium in partial corpus callostomy and the brain stem in complete corpus callostomy becomes the route for inter-hemispheric communication.

Alien Hand Syndrome

• Patients with brain damage from surgery, stroke or infection sometimes develop a syndrome in which they can feel sensations in their hand, but they don't feel responsible for nor able to control its movements. In patients with a corpus callostomy, alien hand syndrome most often manifests as uncontrolled but purposeful movements of the nondominant hand.