Early research Gazzaniga is known for his work in cognitive neuroscience. His research with split-brain patients has helped to understand the distinct roles of the left and right hemispheres of the brain. In split-brain patients the
corpus callosum, the giant nerve bundle that connects the right and left hemispheres had been severed to limit the transmission of nerve impulses across the brain in the hopes of decreasing previously intractable seizures. The original series of split-brain patients, whose callosotomies had been done in the 1930s in
Rochester, New York had been previously tested, and no evidence was found that there was any disruption of the interhemispheric transfer of information after
callosotomy. Later, however, Sperry and his graduate student Ron Myers found that severing the corpus callosum in monkeys did block the transfer of information. As a first-year graduate student at Caltech, Gazzaniga, convinced by the monkey research that transfer of information would be interrupted, began to test the first California split-brain patient (patient W.J.) with a testing procedure that had not been done on the previous series of split-brain patients. He had to present information to one hemisphere only in order for his experiment to work. The anatomy of the optic nerve allowed Gazzaniga to communicate solely to one hemisphere or the other. Visual information flashed to the right side of the visual field of both eyes is sent to the left hemisphere, and visual information flashed to the left side of the visual field of both eyes is sent to the right hemisphere. He designed an apparatus that flashed a letter, number or symbol onto a screen to either the right or left visual field while the patient focused on a central point. By fixating on a central point, the quickly flashed figure (200ms) could be isolated to a particular visual field.
Patient W.J. Patient W.J. was a
World War II paratrooper, the first of a series of patients that underwent a callosotomy on the West Coast. He had developed
grand mal seizures after a German soldier knocked him out with a rifle butt after a parachute jump behind enemy lines. When it was suggested that he might benefit from a callosotomy, he was having anywhere from one grand mal seizure a week to seven a day, each requiring a full day to recover. He was ready to risk it. The surgery, which severed his entire corpus callosum and
anterior commissure, was a success. W.J. had no more seizures and said he felt no different (except for being seizure free) than he did before surgery. Before surgery, Gazzaniga tested W.J.'s brain functions. This included identifying stimuli presented to the left and right visual fields and identifying objects placed in his hands that were hidden from view, all of which he could easily do. After he had the surgery, the test results were different. When a picture of an object was flashed to his right visual field and he was asked if he saw anything, he quickly named the object. When a picture was flashed to his left visual field, however, he denied seeing anything. Then a circle was flashed on the screen and he was asked to point to whatever he had seen with whichever hand he wished. When the circle was flashed to the right
visual field, he pointed to where it had been with his right hand, which is controlled by the left hemisphere. When it was flashed to his left visual field, even though he denied seeing anything, he pointed to where it had been with his left hand, controlled by the right hemisphere. This seemingly simple test showed that each hemisphere saw a circle when it was shown in the opposite visual field, and each
hemisphere, separate from the other, could guide the
contralateral hand, which it controls, to point to the circle it had seen, but only the left hemisphere could talk about it. Neither hemisphere knew what the other had seen! Another experiment revealed the right hemisphere's was adept at visuospatial relations. A card showing a pattern produced by a set of blocks was put on a table in front of W.J. He was asked to copy the pattern using a set of blocks with his left hand, which was quickly able to reproduce the pattern. When it was his right hand's turn, it fumbled around haphazardly. Indeed, seeing what his right hand was up to, the left hand kept trying to help the fumbling right hand. W.J. had to actually sit on his left hand to stop it from interfering: two different mental control systems were competing with each other to solve the problem. These experiments opened the door to years of research by Gazzaniga and colleagues that has revealed that severing the callosum prevents the transfer of perceptual, sensory, motor, gnostic ( previously learned information about objects, persons, or places collected from our senses) and other types of information between the left and right cerebral hemispheres. Extensive research has shown that many of the brains processes are lateralized, such as speech and language to the left hemisphere, along with analytical thinking and the capacity to interpret (not necessarily correctly) behavior and unconsciously driven emotional states, while visuospatial processing, facial recognition, attentional monitoring, and the ascribing of beliefs to others are right hemisphere processes.
Patient P.S. Patient P.S. at age 20 months developed a high fever and had many right-sided seizures, which became generalized, with a seizure focus over the left temporal region. He appeared to develop normally until age 10 when generalized seizures recurred spontaneously and became intractable. At age 14 he had a complete surgical section of the corpus callosum. He was also the first split-brain patient studied from the east coast series who had a full callosotomy with an intact anterior commissure. He had absolutely no interhemispheric transfer of visual information, and although only his left hemisphere could speak, he was the first split-brain patient in that series who demonstrated extensive language comprehension in the right hemisphere. For example, if he were asked to name an object in a picture presented to his left visual field (right hemisphere), while he could not answer with speech, he spelled out the appropriate word with Scrabble tiles using his left hand. Every time, every picture. Even though he was right-handed, he could also roughly write words with his left hand. P.S.'s right hemisphere's verbal skills are unusual. Review studies on 3 series of patients who had had brain bisection found that right hemisphere language in split-brain patients happens infrequently. It is almost always attributable to early left-hemisphere brain damage, but see Patient J.W. below. Gazzaniga and his graduate student
Joseph LeDoux realized that P.S. presented them with the opportunity to directly question his right hemisphere: Would it be able to answer subjective and personal questions and, more specifically, did it possess its own sense of identity? To do this, they verbally asked, "Who
blank?" then flashed the rest of the sentence "are you?" to his left visual field only and thus his right hemisphere. He spelled out "Paul" (his first name) with his left hand using the tiles. With the next question, they asked, “Would you spell your favorite
blank” and then flashed “girl” to his left visual field. He shrugged and shook his head: His left hemisphere had seen nothing. But then he giggled and blushed. The right hemisphere saw and read the word “girl” and the right hemisphere’s comprehension of the word caused him to blush and giggle like most young teenage boys would have at the question. Meanwhile, the left hemisphere, which had not seen "girl," had no clue why he was blushing and giggling. Then his left hand reached out for 3 Scrabble tiles and spelled out the name “Liz.” Another telling question asked the right hemisphere what job he would pick. He spelled out “automobile race” with his left hand, though shortly after the end of the session, he was asked the entire question out loud (so his left hemisphere heard it), and his left speaking hemisphere answered, “Oh, be a draftsman.” Each hemisphere had a separate goal. The experimental session ended after asking the right hemisphere to spell out its mood. The left hand spelled out "good." These results suggested to LeDoux and Gazzaniga that they may be observing a basic mental mechanism in the left hemisphere that we all possess. They suggested that “the conscious verbal self is not always privy to the origin of our actions, and when it observes the person behaving for unknown reasons, it attributes cause to the action as if it knows for certain, but in fact it does not. It is as if the verbal self looks out and sees what the person is doing, and from that knowledge it interprets a reality.” Four months after her surgery, her right hemisphere could write simple answers and was able to carry out verbal commands. For example, if the command “smile” was flashed to her right hemisphere, V.P. could do it. Ask her why she was smiling and her left hemisphere would assert some made up answer. So V.P. was the second split-brain patient in the East Coast series whose right hemisphere had some verbal capacity. Gazzaniga wondered if he could create a mood state in the right hemisphere, study whether the left hemisphere was aware of it, and if so, how would it deal with it? A previous experiment with split-brain monkeys had shown that emotional states appear to transfer between the hemispheres subcortically, that is, areas not affected by callosotomy, so it seemed possible. Gazzaniga showed V.P's right hemisphere a scary clip from a movie where a man pushed another man off a balcony and threw a fire bomb on top of him. Then she was asked what she had seen. She said, “I don’t really know what I saw. I think just a white flash.” When asked if it made her feel any emotions she answered, “I don’t really know why, but I’m kind of scared. I feel jumpy, I think maybe I don’t like this room, or maybe it’s you.” She said to one of the research assistants, “I know I like Dr. Gazzaniga, but right now I’m scared of him for some reason.” She felt the emotional response to the video her right hemisphere had seen but had no idea what caused it. She looked around to come up with an hoc answer. Gazzaniga explained, "The left-brain interpreter had to explain why she felt scared. The information it received from the environment was that I was in the room asking questions and that nothing else was wrong. The first makes-sense explanation it arrived at was that I was scaring her." Gazzaniga later called this capacity to interpret behavior and unconsciously driven emotional states 'the Interpreter.' This system takes the chaos of both internally and externally generated information that is constantly bombarding each of us and tries to make sense of it all. It weaves a story about events, even felt emotions that can go beyond the actual available information or it can ignore pertinent information. Gazzaniga postulates that the interpreter underlies the human drive to seek explanations for why events occur. This system has proven to be helpful for survival, but also is not always accurate.
Patient J.W. Patient J.W. suffered a concussive head trauma at age 13, after which he began to have brief absence spells that went untreated. At 19, he experienced his first grand mal seizure. The frequency of the seizures increased and were intractable with medication. In 1979, when he was 26 years old, he underwent a two-stage callosotomy. Immediately following both surgeries, his right hemisphere had the capacity to understand spoken and written language, meaning that he had a right hemisphere semantic system, but was unable to speak. For example, the left hand could make a picture-word correspondence: Lateralize a picture of a bird to J.W.'s right hemisphere and his left hand would point to the written word "bird." Lateralize the word "zebra" to his right hemisphere and his left hand would point to a picture of a zebra. Unexpectedly eleven years later, while evaluating visual field stabilizing equipment, J.W.'s right hemisphere started to vocally name pictures that were presented to his right hemisphere. Over the following several years, this ability continued to increase. Up until then, the previously reported post-callosotomy dynamic periods of right hemisphere language capacity suggested that the right hemisphere could only develop language skills in the absence of the left hemisphere when there had been damage to the left hemisphere in childhood. Another interpretation of the data was that observations of right hemisphere
language development were restricted by the limited life span of postoperative adult patients. J.W. was the first split-brain patient to demonstrate an increasing ability for right hemisphere speech many years after his callosotomy. While long-term functional plasticity has been suggested in adults, documentation of such is scarce. == Selected publications ==