Split-Brains: Interhemispheric Exchange in Creativity

Joseph E, Bogen, USC, UCLA, Caltech

Glenda M. Bogen, Pasadena, California

I. Stages in Creativity
II. The Split-Brain
III. The Fundamental Finding
IV. Creativity
V The Lack of Creativity
VI. Summary

Brain Stem The continuation upwards of the spinal cord.

Callosotomy Operation in which the fibers of the corpus callosum are cut--usually done to prevent seizure activity from spreading from one cerebral hemisphere to the other.

Cerebral Hemisphere One of the two halves of the cerebrum. each hemisphere sitting on top of one limb of the Y-shaped upper end of the brain stem.

Cerebrum The greatly expanded top of the nervous system, overhanging and largely hiding the brain stem.

Corpus Callosum A large collection of about 200 million nerve fibers that directly connects the two cerebral hemispheres.

Hemispherectomy Removal of one cerebral hemisphere by combining a complete callosotomy with transection of the nerve fibers connecting the hemisphere with the brain stem. Usually done to treat medically intractable seizure disorders that are spreading from a badly scarred nonfunctional hemisphere to a relatively intact hemisphere.

Split-Brain The result of a complete callosotomy; the two hemispheres still remain in communication via their connections through the Y-shaped upper end of the brain stem.

Explanations of creativity in terms of brain function are rare. One brain-based theory was advanced by the authors in 1969 and expanded by others. The theory arose from observations of humans who had the SPLIT-BRAIN operation. This surgery successfully treated their epilepsy and made it possible for them to join in laboratory experiments, which led to a Nobel Prize for Roger W. Sperry, with whom the authors collaborated for more than 30 years. This article first offers some observations on creativity, emphasizing its development through several stages. Then a brief description of split brain behavior is presented. Third, two implications of the split-brain research are considered: (a) each cerebral hemisphere can function to a significant extent independently and (b) the two hemispheres function differently. The article concludes with the authors' views on both creativity and a lack of creativity,
I. STAGES IN CREATIVITY
Creativity provides a workable approach to an unsolved problem or a previously unrecognized opportunity. Often, the essence of the approach appears rather suddenly and further details are then filled in. Many people have pointed out that creativity occurs through several stages.
Hermann Helmholtz, the great physicist, described the way in which his most important new thoughts had come to him. He said that after a period of lengthy investigation. "happy ideas come unexpectedly, without effort, like an inspiration. So far as I am concerned, they have never come to me when my mind was fatigued, or when I was at my working table . They came particularly readily during the slow ascent of wooded hills on a sunny day."
Henri Poincare, in his book Science and Method, described in vivid detail the successive stages of his great mathematical discoveries. They came to him after long preparation and a period of incubation during which no conscious mathematical thinking was done. He wrote, "I went away to spend a few days at the seaside and thought of entirely different things. One day as I was walking can the cliff the idea came to me."
Such stories are not restricted to scientists. Supreme Court chief justice Rehnquist wrote, "I began to realize that some of my best insights came not during my enforced thinking periods in my chambers, but while was shaving in the morning, driving to work or just walking from one place td another."
To result in a successful creation, an inspiration must next be verified to see that the idea really works. This verification phase is similar to the preparation phase in that the process is often logical, mathematical, or literary and is consciously deliberate. Graham Wallas suggested in 1926 that creativity proceeds in four distinct phases: preparation, incubation, illumination, and verification.
To produce something both novel and meaningful one must have a period of preparation. This involves acquiring a large fund of information. Following preparation is a period of incubation during which time the information is rearranged, typically while one is unaware of the process. Next is illumination. Almost everyone is familiar with the cartoonist's use of a light bulb to symbolize the instant illumination of an idea. Last is necessary a phase of deliberate reorganization and refinement, readily describable by the creator, to test and polish the final product .
What can be the physiologic basis for this succession of stages! During incubation, some very productive thinking goes on, which is inaccessible to verbal output (in that one cannot tell how it went on) and whose result can become available in a sudden insight. Where does this thinking take place! To say that it comes from the heart describes the quality rather than the origin. To say that it comes from intuition is merely to rename it rather than to give it a physiologic source. It surely requires an elaborate neuronal system, of a size, complexity, and activity level comparable to that organ-namely, the left hemisphere--that produces the richness of human language. It is likely that much of the thinking that goes on during incubation takes place in the human right hemisphere. [See INCUBATION; INTUITION . ]
By contrast, the preparation and verification phases seem more left hemispheric. One sees the likelihood of a greater than usual interhemispheric communication during an individual's more intuitive moments, an interaction dependent on the corpus callosum.
II. THE SPLIT-BRAIN
The corpus callosum, with more than 200 million nerve fibers, constitutes 3. system larger than the sum of all systems ascending to and descending from the cerebral hemispheres. The central location and the large size of the corpus callosum, especially in humans, have for centuries suggested an important role in mentation. During the past 30 years, a large number and variety of experiments have made it clear that the corpus callosum can transfer high-level information from one hemisphere to the other. Moreover, we now know that the hemispheres are not so much "major" and "minor" as they are complementary and that each hemisphere is capable of thinking on its own, in Its own way. Much of this information has come from cutting the corpus callosum, that is, the split-brain operation.
The term split-brain has several meanings. Applied to the human, it denotes complete callosal section--an operation that has been performed for medically intractable epilepsy to stop the spread of seizure activity from one hemisphere to the other. Our own split-brain patients had complete cerebral commissurotomy, including anterior commissure, and dorsal and ventral hippocampal commissures, as well as complete callosotomy. But it is now common to use the term split-brain to refer to cases of complete callosotomy alone, because they show most of the same signs and symptoms. When patients who have had a complete callosotomy have recovered from the acute operative effects and reach a fairly stable state, they show a variety of phenomena that can be grouped under four headings
A. Social Ordinariness
One of the most remarkable results is that In ordinary social situations the patients are indistinguishable from normal in spite of the cutting of more than 200 million nerve fibers. Special testing methods are needed to expose their deficits. These usually involve restricting the input to only one hemisphere--for example, by putting an object into one hand, with vision occluded.
B. Lack of Interhemispheric Transfer
A wide variety of situations have been developed to show that the human subjects are in this respect the same as split-brain cats and monkeys. A typical example is the inability of the split-brain person (or monkey) to retrieve with one hand an object palpated with the other, although same-hand retrieval is normal.
C. Hemispheric Specialization Effects
The hemispheric specialization typical of human subjects results in phenomena not seen in split-brain animals. A typical example is the inability of right-handers to name or describe an object in the left hand, even when it is being appropriately manipulated and can be reliably retrieved from a collection when the subject has previously felt it with the same, retrieving hand.
D. Compensatory Strategies
Split-brain subjects progressively acquire a variety of strategies for circumventing their interhemispheric transfer deficits. A common example is for the patient to speak out loud the name of an object palpated in the right hand; because the right hemisphere can recognize many individual words, the object can then be retrieved with the left hand.
III. THE FUNDAMENTAL FINDING
The fundamental finding from the split-brain is that the two cerebral hemispheres can function independently and simultaneously, in parallel. This point has been confirmed in dozens of human patients in several different institutions (unlike those famous, individual cases on which so much neurologic theorizing has been based). Moreover, the fact of hemispheric independence has been repeatedly confirmed in experiments with cats and monkeys that never had epilepsy or the other qualifying factors that have been recurrently pointed to by persons unwilling to recognize the fundamental finding because of its startling implications.
IV. CREATIVITY
If learning can proceed simultaneously, independently and differently in each hemisphere, so may problem solving. This contributes to a less predictable--that is, a less stimulus-bound-behavior In other words, specialization of the hemispheres for different trains of thought greatly increases the flexibility of the ensemble. Such differentiation necessarily produces a concomitant decrease in stability. The successful expansion of the human species (so far) suggests that the loss of stability is less important than the gain in flexibility. (See PROBLEM SOLVING.)
Creativity has not only made the human species dominant (and dangerous) on the earth; what may be more important for each of us is that it gives value and purpose to human existence. Creativity requires more than the propositional skills and logical thought of the left hemisphere; it also needs the cultivation and collaboration of the other side of the brain. There is as yet no clear consensus on how best to describe the cognitive differences between the hemispheres. Whatever terms are used (e.g., propositional versus appositional), what is essential for our theory is the well established fact that in most humans the two cerebral hemispheres function quite differently. We believe that this involves, indeed requires, a significant degree of hemispheric independence, such that the interhemispheric exchange is much of the time incomplete.
No one supposes that all creativity involves the corpus callosum. The left hemisphere alone, either following right hemispherectomy or isolated from the right by callosotomy, is capable of a full range of verbal expression, including generation of an unlimited number of novel sentences. But when a solution requires combining of "dual memory codes, verbal and imaginal" (as Brenda Milner put It) one readily recognizes an important role for the corpus callosum.
V.THE LACK OF CREATIVITY
If some kinds of creativity are dependent on a transcallosal interhemispheric exchange, there are three obvious explanations for its absence. There may be first of all a deficiency of technical competence in 3 suitable medium; in the case of literary as well as mathematical creativity this is easily seen as a lack of propositional skill.
Second, many persons possess technical proficiency in music, drawing, or writing whose production is devoid of those innovative and informative values that distinguish an artist from a performer. We are accustomed to hear, these days, of the "culturally disadvantaged," usually referring to persons whose propositional potential has remained undeveloped for lack of proper schooling. There is likely a parallel lack of appositional development in persons whose education has narrowly emphasized reading, writing, and their concomitants. Third, there must be the possibility of a heightened communication between the two hemispheres, overcoming temporarily the ongoing lack of transfer that has allowed independent processing.
The foregoing considerations, especially the extent of hemispheric exchange, led to a series of experiments by Warren TenHouten and colleagues in which split brain patients (and controls) were studied by interview and EEG with respect to their reactions to a short movie containing symbols highly loaded with affective significance respecting separation and death. These experimental results, as well as the similarity between split-brain patients and persons who have experienced, with psychosomatic or addictive disorders, an impoverishment of their fantasy life without being bothered by it, led to the hypothesis of "functional commissurotomy" by Klaus D. Hoppe. That is, alexithymic patients appeared to be deprived, as were the split-brain patients, of what Hoppe has termed "hemispheric dissociation," which facilitates symbolexia, the verbal expression of empathic identifications with symbolized affective states.
The conditions for a fluctuation In callosal transmission have yet to be adequately explored. One consideration is that inspiration occurs not only in repose but often in striving under pressure. In any case, variations in hemispheric exchange are clearly contingent on appropriate affective states.
VI. SUMMARY
A duality of mind is readily demonstrable in split brain humans, and evidence is steadily accumulating that ongoing interhemispheric communication is incomplete in the intact brain. It is now certain that the corpus callosum can transfer high-level information from one hemisphere to another. When we take into account the well-established principle of hemispheric specialization, the alexithymia in spite of the impressive normality of split-brain humans in ordinary social situations, a physiologic explanation for at least some forms of creativity seems close at hand. What is required is a partial (and transiently reversible) hemispheric independence during which lateralized cognition can occur and is responsible for the dissociation of preparation from incubation. A momentary suspension of this partial independence could account for the illumination that precedes subsequent deliberate verification. From this point of view, we can understand better tile observation of Frederic Bremer, who wrote years ago that the corpus callosum subserves "the highest and most elaborate activities of the brain"--in a word, creativity.
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