Split-brain
From Free net encyclopedia
Split-brain is a lay term to describe the result when the corpus callosum connecting the two halves of the brain is severed to some degree. With a severed corpus callosum, the two hemispheres of the brain are forced to function independently of each other. The surgical operation to produce this condition is called corpus callosotomy. It is rarely performed, usually in the case of severe epilepsy; to mitigate the risk of accidental physical injury by reducing the severity and violence of epileptic seizures. This surgery is very successful, but it is only used as a last resort. A patient with a split brain, when shown an image in his or her left visual field (the left half of what each eye sees), will be unable to name what he or she has seen. This is because the speech control center is in the left side of the brain in most people and the image from the left visual field is sent only to the right side of the brain. Since the two sides of the brain cannot communicate, the patient can't name what he or she is seeing. The person can, however, pick up a corresponding object with their left hand, since that hand is controlled by the right side of their brain. Most modern callosotomies involve only the anterior portion of the corpus callosum, reflecting the fact that the frontal and temporal lobes are the most commonly involved in the genesis of seizures. The deficits from this modified procedure are milder; some patients have no side effects whatsoever. Some of the earliest split brain research was carried out by Roger Wolcott Sperry. Sperry began his research on animals. He severed the corpus callosums of his subjects and conducted tests on them in order to discover what changes the surgery had produces in their behaviors. Sperry was joined by Michael Gazzaniga in the early 1960s, and they went on to do split-brain research on the human brain. In 1966, ten corpus callosotomies had been performed, and four of the ten patients agreed to be studied by Sperry and Gazzaniga. Their research would attempt to discover how the two halves of the human brain function when they are separated from each other. The researchers developed visual, tactile, auditory, and many other tests to explore the cognitive abilities of their patients. The visual tests were set up so that a picture, word, or word segment was presented to only one of the patient’s brain hemispheres. Through these tests, Sperry and Gazzaniga discovered that both the right and left hemispheres of the brain are equally capable of visual perception. However, because the center for speech is in the left hemisphere, that side of the brain had to see the stimulus to verbally identify it. The tactile tests allowed the patients to feel an object or block letters that they were unable to see. After conducting these tests, the researchers learned that objects felt with the right hand were easy for the patients to identify verbally, confirming that the left hemisphere is the verbal center. However, objects held in the left hand were understood by patients, but they were unable to verbally communicate this understanding. The researchers discovered that the right hemisphere can comprehend language in a nonverbal way, and that it is good at thinking about and analyzing the stimuli that is presented to it. The right hemisphere was also found to be better at visual tasks involving shapes and spatial relationships. The researchers concluded that every human being has two complex, individual brains residing in his or her skull. This conclusion is not universally agreed upon, but the research conducted by Sperry and Gazzaniga has been responsible for vast improvements in the understanding of the human brain and how it functions. As a result of this improved understanding, great advancements have been made in the world of medicine.
Results from this research have led to important theories on the lateralization of brain function.
External links
- Detail on the callosotomy procedure from epilepsy.com
- Interesting summary with further links to follow
- An animated game that illustrates the split-brain experiments.