Insights From a Brain Divided
Working about 50 years ago, Roger Sperry teamed up with a surgeon, Joseph Bogen to start an extremely productive line of research. Patients with intractable grand mal epilepsy had been shown to benefit from a very radical surgical procedure: separating the left hemisphere from the right. Seizures start from a small piece of brain firing rapidly, and if it can recruit other parts of the brain it can bring on the full grand mal episode. Separating the left and right hemispheres prevented some of those seizures from occurring by preventing early recruitment from the other hemisphere. In the human brain there is a very large connection between the left and right hemispheres called the corpus callosum. It runs as a long, flat band of connections between left and right from near the front of the brain to the rear. It is supplemented in the front by the anterior commissure, which is a round commissure connecting the left and right hemispheres.
Early in the long series of experiments Sperry was joined by Michael Gazzaniga, and it was Gazzaniga who took over the human experiments when Sperry went back to animal experiments. One of the first questions raised by these operations, was whether there was just one individual or two after the split-brain operation was carried out. It turned out that the very first results were quite shocking—it appeared that there was almost no change in the person aside from the abrupt slacking off of the seizures. IQ remained the same and personality was the same—and the person did not report any “missing parts”. The experimenters believe they understand why there is no report of missing the left or the right side of the body. When a person loses sight in an eye or hearing in an ear it is readily detected as the brain detects the lack of information input. But when a stroke occurs at the very top of the information processing chain, such as the cerebral cortex there is often no report of any missing body part because the part of the brain that would detect the missing information is in fact the part that is now defunct. So that in some persons with a high-level stroke on the left side of the brain they do not miss the right half of visual space that is processed by the injured cortex—instead they simply are not aware that it is there, it is ignored. So that the person may eat the food on the left half of the plate but ignore the food on the right half. Thus, it appears that the separated halves of the brain do not miss one another, but they can cooperate because they are aware of each other’s existence without “missing” the input from each other.
The cooperation between the hemispheres was not complete, however, but did get better with learning over time. The commissures between the hemispheres permit the higher levels of the cortex to coordinate their activities. One patient described buttoning his shirt with his right hand and finding the left hand was following along unbuttoning, but he had no idea why. Another described going to the grocery store and spending much more time than usual because she knew what item she wanted to pick up, but the left arm would work to prevent the right arm from picking up the item. She also had difficulty getting dressed because the two hemispheres did not agree on the appropriate clothing. Some actions are learned at a lower level in the nervous system, like the well-learned task of tying a shoelace, and those kind of actions were never bothered. Only the “high-level” choices were affected by the split-brain operation. After a few months the two hemispheres learned how to cooperate, and not interfere with each other.
Are Left and Right Different?
Many of the early findings from these patients was focused how the abilities of each of the hemispheres differed. This lead to much of the talk in the 1970’s and 80’s about creative/artistic abilities being in the right hemisphere and the linguistic abilities being in the left hemisphere. Some of that was over the top, but still reflected the basic findings. In persons who are right-handed their language abilities are located in the left hemisphere as are their math and logic abilities. The right hemisphere is where images of objects, spatial relationships and other more visually-based abilities reside. The right hemisphere also is where music and rhythm is both appreciated and generated. Also, the ability to recognize faces and the emotions those faces express resides in the right hemisphere, as does the detecting, processing and generation of emotions in general.
Most of the research into left-right brain functions was based on the fact that our visual world is split exactly in half. Everything to the left of your nose goes to the right hemisphere, and everything to the right of your nose goes to the left hemisphere. Thus, the experimenters could flash pictures separately to the left and right visual fields, thereby giving each hemisphere a separate picture. The left brain could speak what it saw, but the right had to draw what it saw because it had no ability to speak. It turns out that despite the left hand being the more poorly controlled hand (these were right-handed people), they could draw very well with their left hands (which is controlled by the right hemisphere). [Remember, everything in the brain is crossed: the left hemisphere controls the right hand and sees the right visual field; the right hemisphere controls the left hand and sees the left visual field.] Interestingly, the right hands were very poor at drawing—only stick figures could be done by the left hemisphere, and it was unable to copy simple figures like squares, circles and cubes. The left hemisphere is devoid of spatial ability.
The right hemisphere is quite good at spatial relationships, but is unable to see how things are causally connected except in the most simple of cases. It is very practical in how it sees the world and processes information. For instance, if the right hemisphere sees a billiard ball strike another ball, transferring its momentum to the second ball, that is fine. If the first ball stops short of the second ball, yet the second ball rolls away, it sees this as magic—as it should. The left hemisphere, on the other hand sees both instances as logical and ordinary—as it should not. But if a large cube is struck in random fashion by either a small green cube or a small red cube, and the large cube only lights up when struck by the green cube, the right hemisphere cannot see the logical connection between the big cube lighting up only when struck by the green cube. The left hemisphere has no difficulty seeing the logical connection. The left hemisphere finds it easy and comfortable to “connect the dots”, while the right hemisphere is mostly content with “just the facts” and no conclusions.
The right hemisphere has some crude language abilities. It can read words that are in common spoken language and can spell (using Scrabble letters) some simple words. When a 14 year-old boy was asked verbally, “Who is your favorite…” and then the words ‘girl friend’ were flashed only to his right hemisphere, he responded with a blush and some giggling—his left hemisphere could not say why. However, his left hand could slowly construct the girl’s nickname, Liz, from the Scrabble letters. This shows not only the small language ability of the right hemisphere, but also its involvement with emotions.
An example of how the right hemisphere handles emotional nuance—and takes a leading role in moral reasoning was shown in an experiment asking patients to respond to a commonly used moral test. The experimenters read the story out loud, and only quizzed the left hemisphere. They told of a man who accidentally confused poison with sugar and killed his boss. Another man wished to kill his boss, but mistakenly gave him sugar instead of poison, leaving him very much alive. They asked if both men were equally moral in their actions, or whether one was more reprehensible than the other. Most folks believe that the person intending to kill is worse morally than the one causing death by accident. The logically superior left hemisphere thought they were equally bad. Thus, it was surmised, that most of us, with intact connections between left and right hemispheres, use input from our emotionally superior right hemisphere to see the moral difference.
The right hemisphere is thought to posses the capability of watching other people’s behavior and expressions, thereby understanding what they are thinking and feeling. This ability of the right hemisphere is very important in how humans get along. Language does not provide all the information humans need to live and work with each other—we need to have an intuitive feel for what others around us are likely thinking and feeling. This capability seems a perfect fit for the hemisphere that evaluates faces and works out the nuances of the appropriate emotional reactions.
There is another difference between the left and right hemispheres that is not so much based on the split-brain experiments, as on strokes on one side of the brain or the other, and that is the emotional bias inherent in each hemisphere. When the left hemisphere is damaged the patient tends to become depressed, while tending to becoming overly optimistic or manic when the right hemisphere is damaged. Findings from other scientific approaches have also supported the idea that the left hemisphere tends to drive us toward a positive mood, while the right tends to move us toward a more depressed state.
Likely the most significant finding of the split-brain experiments was the discovery of the “interpreter”. This came about by showing the left and the right hemispheres a different set of pictures. The left hemisphere was shown a picture, a chicken claw and then it had to chose a picture that went with it from among four pictures—which both hemispheres could see—one of which was a chicken coop. The right hemisphere was shown a snow scene and then had to chose a picture from among the same four being seen by both hemispheres. It chose a snow shovel. When the left hemisphere (which had seen the chicken claw, but not the snow scene) was asked why the right hemisphere had chosen the shovel it quickly replied, “Why to help clean out the chicken coop.” Notice, it did not say, “I don’t know.” It simply went ahead and made up a story that covered the facts that it knew. And it did it on the spot, no hesitation involved. These kinds of results from numerous experiments show that the left hemisphere has an “interpreter”. The interpreter goes about explaining what is happening at the moment, using the facts that it has on hand, and constructing a story that covers those facts as best it can.
The discovery of the interpreter and its function in our lives gives great insight into how our conscious lives are constructed, and how we see our lives unfolding. It should give us all pause, because the ramifications are quite profound. Much, perhaps most, of our lives are being carried out by a brain that is running at an unconscious level and the interpreter is following along with its ability to use whatever facts it has at hand to make up a “best-fit” story about what we are doing.
Gazzaniga illustrates, with a simple story, how the interpreter gets the facts wrong, but gives us a believable narrative when we hit our thumb with a hammer. The hit on the thumb gives rise to a pain signal that elicits a spinal reflex that pulls back the hand in less than a quarter second. But the pain signal will not even reach the brain for half a second and that is when we become aware of the situation. However, the interpreter gives us the story that we consciously felt the pain, withdrew the hand and cried out. That was not the true sequence, but it is one that fits the logic of how the interpreter sees the world. One consequence of knowing that the interpreter is on the job is to accept that you are living your life on a “tape-delay” system. You are following along the actions of your brain by about a half second delay.
Everyone is familiar with the interpreter, it is that voice that you hear in your head all the time, which you think of as ‘you’. Knowing that the interpreter is quite willing to make up a “best-fit” story to explain your behavior gnaws at the idea that we know and choose our actions, and that we have free will. If your brain does most of its behavior at an unconscious level and then your interpreter comes along to “explain” it to you, it leaves us with some questions. How did the unconscious brain make its decisions? How much control do you really have in generating your behavior?
The interpreter serves us well in explaining to us, moment to moment, what we are seeing, how we are reacting, and how the world looks to us right now—it constructs a narrative that makes sense out of the world that we are experiencing. It saves us from the possible alternative fate of some confusing meld of left and right hemisphere outputs. Perhaps another way of looking at the interpreter is that it gives us a single, unified view of the world, and it provides us with a felling of “self”. But it does not really have access to all the decision making that took place at an unconscious level—it is just guessing.
Blending the concept of the interpreter with other scientists concepts of self or conscious thought processes is difficult. If you have read the earlier blogs in this series you will recall reading about system 1 and system 2. System 1 was unconscious and fast, system 2 was conscious and slow. The interpreter comes from insights gained from split-brain research, while the concept of systems 1 and 2 was based mainly on research in cognitive decision-making and risk-taking. The interpreter cannot be completely morphed into being system 1 or 2—it has some of the characteristics of both. The interpreter is conscious, as is much of system 2. But the interpreter is less than system 2, while certainly being part of it since it is conscious. However, the interpreter seems to operate with one of the characteristics of system 1, which is that both rely only on the facts currently in mind to explain what is going on. System 2 must be called in to override system 1 if more information is required to understand the current situation.
Other scientists have seen the concept of self as more encompassing then the interpreter. But the interpreter’s function was derived from experiments in split-brain patients. It may be that in normal brains with left and right hemispheres connected, the interpreter might take on more nuanced views of the world using input from the right hemisphere. Other scientific views of self would incorporate more awareness of emotive feelings, which would need the input of the right hemisphere to invest those feelings in the self. However, the existence of a story teller in the left hemisphere that seems to operate with some of the rules that govern the fast processing of system 1 (such as explaining behavior using only the facts known at the moment to the interpreter), changes the way in which we must look at ourselves and think about our behavior.
Interestingly, in folks with right hemisphere strokes the interpreter can begin constructing stories that are quite fantastical. The right hemisphere, in its parietal region, has an area devoted to monitoring the interpreter and reining it in if it starts going overboard with stories that deviate too far from the possible. When this is missing, as in a right hemisphere parietal stroke, the interpreter knows no bounds.
The findings from the split-brain experiments raise some interesting questions: What did the brain gain by making the hemispheres specialize? Since both sides of the brain have the same nuclei, how did the right side get to handle all the high-level emotional control, while the left got to handle logical thinking? As a secondary to that question, what role do the nuclei play that are in the hemisphere that is not dominate for their function (e.g., the emotional nuclei in the left hemisphere)? We do not have any solid answers for any of these questions. All we know so far is that at the top level the specialization seems fairly complete.
“Who’s in Charge?: Free Will and the Science of the Brain” Michael S. Gazzaniga, 2011.