A Brief History of Split-Brain Research

As part of my research, I wanted to learn about the history of split-brain discoveries. I read a very interesting article from the scientific journal Nature. This post will cover many of the highlights in the history of discoveries by the leading scientists in split-brain resarch.

The incredible procedure known as the corpus callosotomy was first used in Rochester, New York in the 1940’s. It was performed on a group of 26 people that all suffered from extreme epilepsy, and the goal was to stop the patients’ seizures by isolating the excessive brain activity to one hemisphere of the brain. Unfortunately, the surgery failed to prevent the seizures at first, and one theory suggests that this was because the two hemispheres were not completely separated. It was not until 1962 that one of the patients showed improvement following the surgery. While the procedure is highly invasive and can generally be replaced by drug treatments for epileptic patients, a pair of scientists, Roger Sperry and Michael Gazzaniga, wanted to learn more about how the brain operates as two separate machines, and these split-brain patients were the perfect opportunity for them. Earlier  studies of the split-brain patients documented that the patients had no change in behavior or brain functioning, but Sperry and Gazzaniga were perplexed by this and decided to investigate further.

Their first subject was a World War II veteran who underwent a corpus callosotomy to stop his seizures which were due to a serious head trauma during the war. They experimented on him by flashing stimuli to either his right or left visual field, feeding the information to the brain hemisphere opposite the visual field. He was told to press a button and tell the researchers what he saw whenever a stimulus appeared. When the stimulus was in his right visual field, the information was being sent to his left hemisphere, and he would immediately press the button and tell the scientists what he saw. But when the stimulus was in his left visual field, the information was sent to his right hemisphere (the side that does not produce language), and he told the scientists that he did not see anything. What was interesting though, was that he would still press the button with his left hand even though he claimed not to have seen anything. Sperry and Gazzaniga realized that the two sides of his brain were operating completely independently of one another and were not aware of what the other side was processing.

It was hard for the scientists to find more split-brain patients to study that did not have other serious neurological disorders that would interfere with their experiments. But in the 1980’s, split-brain research became more widespread when a few more ideal subjects were found. One of the major focuses of split-brain research was to learn if the right brain was capable of processing language, despite the fact that it can not produce speech. Gazzaniga conducted a study with a young boy with a split brain to find out. He asks the boy “who is your favorite girlfriend?” But the word “girlfriend” was only flashed to the boy’s right hemisphere. The boy responded by saying that he did not see any word, but then he giggled and blushed, indicating that he did indeed see the full question. He then used his left hand to arrange three scrabble tiles to spell the word “LIZ,” answering the question. This supported that the right hemisphere is capable of processing language, which was huge in the world of neuroscience. It was discovered later through another patient that the right hemisphere actually can produce speech in some cases because the corpus callosotomy affects different patients in different ways.

In 1981, Sperry won the Nobel Prize in Physiology and Medicine for his discoveries, but Gazzaniga continued on with research after Sperry’s death in 1994. Other scientists worked on learning how split-brain patients were able to complete tasks that involved their two hands working together, bimanual tasks. In 2000, a team in New Zealand had split-brain patients carry out various bimanual tasks. They found that the patients were only able to carry out tasks that were familiar to them. For example, a long time fisherman was asked to pantomime tying a fishing line, and he could do it easily. But when asked to pantomime threading a needle, he could not. This showed that certain tasks that are familiar are coordinated at the subcortical level, so the hemispheres do not need to communicate in order to complete them.

Further research on split brains uncovered that the right hemisphere is actually responsible for a lot more than previously thought. More recent studies have shown that the right hemisphere plays a major role in the processing of other people’s emotions and intentions. Through a few experiments focused on moral reasoning, Gazzaniga showed that the left hemisphere alone is incapable of passing correct moral judgement, and that the right hemisphere is actually involved.

As medication has improved, new and better drugs have been used as treatment for epilepsy, and the number of people who undergo a corpus callosotomy rapidly decreases, making it hard for new discoveries about the split brain to be made. Gazzaniga, now known as the “godfather of modern split-brain science,” spends most of his time recording all his observations in his patients over the years. As Gazzaniga put it, “the glory days of split-brain research may be over,” but that does not mean that our knowledge of the rare condition will stop advancing.
Wolman, David. “A Tale of Two Halves.” Nature, vol. 483, 15 Mar. 2012, pp. 260–263. Macmillan Publishers, doi:10.1038/483260a.