BILITERAL BRAIN THEORY

The study of the differences between the hemispheres (halves) of the brain began with an obscure French country doctor, Marc Dax, who noticed that patients who lost their powers of speech following brain injuries sustained damage to only the left sides of their brains. Dax proposed at a medical society meeting in 1836 that speech is controlled by the left side of the brain and, therefore, that the two hemispheres must control different functions. Although Dax’s theory did not receive much attention at the time, it has since been the basis for a great deal of research and interest.

Brain Hemispheres

The human brain consists of two hemispheres that are mirror images of each other. The hemispheres are connected by the corpus callosum, a series of transverse nerve-fiber bundles that transmits information from one brain hemisphere to the other. Each hemisphere controls the movements and sensations of the opposite side of the body; that is, the left hemisphere controls the right side of the body, and the right hemisphere controls the left side of the body.
Human beings are asymmetrical; they are not equally adept at using their right and left sides. Unlike animals, who tend to be right- or left-sided but are equally divided in their preferences, the overwhelming majority of humans favor their right sides. Ninety percent of us are right handed. Furthermore, researchers have discovered that the human brain itself is not symmetrical in its abilities. Although sensory and motor functions are equally divided, many of the higher mental capabilities (such as speech) seem to be controlled primarily by either one hemisphere or the other.
Much of the research that has been conducted on the hemispheres has occurred as a result of studying brain-injured persons or persons who have had their corpora callosa surgically cut for medical reasons (the latter are commonly known as split-brain patients). Mental functions that are hemispherically individualized have been identified in such persons by identifying the functions that have been impaired or eliminated and the side of the brain that was injured. It is then supposed that the injured hemisphere controls those functions.
Such study appears to indicate that the left brain controls a significant portion of the analytical mental functions such as language (both speech and comprehension) and logical and rational capabilities, whereas the right brain controls much of the intuitive capabilities—the ability to produce and appreciate music and art, as well as spatial skills. The hemispheres also seem to differ in their methods of processing information. The left brain tends to process information in a sequential manner, dealing with details and features, whereas the right brain tends to deal with simultaneous relationships and global patterns.
However, the above categorization does not explain our asymmetrical brains. If the above were foolproof, right-handed people all would be logical, organized, and reasonable people, and left-handed people all would be artistic, intuitive, and disorganized.

Left Handedness

Left handedness has become a focal point of study in researchers’ struggles to understand the workings of the human brain. It is not known for sure what causes a person to be left handed. Some scientists believe that left handedness is caused by slight brain damage (caused by insufficient oxygen) to the left hemisphere at birth, forcing the right hemisphere to “take over” the language functions, thus producing a person whose left side is dominant. Others believe that handedness is inherited. They point to the statistics that indicate that two right-handed parents have a 2 percent chance of producing a left-handed child, whereas one left-handed parent and one right-handed parent have a 17 percent chance, and two left-handed parents have a 47 percent chance of having a left-handed child. Still others argue that handedness is behaviorally determined, that it is learned after birth and is not caused by physical trauma or genetics.
“Lefties” differ from “righties” in more ways than their writing hands, which is the most obvious difference. Research does indicate that the brains of left-handed people are organized differently than the brains of right-handed people. Studies have indicated that the speech of some left-handed people actually is controlled by the right hemisphere, which contradicts the right- and left-brain function theories originally presented. Other left-handers appear to have bilateral control of speech, i.e., control shared by both hemispheres. Still others’ speech is controlled by the left hemisphere, just as in the case of right handers. In addition, a disproportionate number of artistic people are left handed, prompting speculation that left handers can develop their right brains (artistic ability, creativity, intuition, etc.) more than right handers.

Some Caveats

Some educators have argued that because we live in a society that values objectivity, logic, reason, and organization more than creativity, intuition, art, and music, our “right brains” are not being developed and utilized as they should. These people point out that our educational methods in general favor “left-brain” processing (testing, reading, writing, reasoning, etc.), while alternative methods of reaching conclusions and learning—such as using intuition or being creative—are devalued. Children in school learn to give the teachers what they want rather than learning to think independently and creatively.
Although these conclusions may be true in terms of sociological processes, they are not necessarily accurate in terms of the popular conceptions of “right brain/left brain.” There is a danger that bilateral brain theory will extend beyond the research of neuropsychologists to become part of the “psychobabble” of the popular culture.
Springer and Deutsch (1989) believe that the hemispheres of the human brain are not as separate and distinct as popular culture believes them to be. Current research seems to indicate that although the hemispheres appear to retain some separate functions, they are more integrated than is commonly realized. Furthermore, there are many components of human existence that have not yet been identified or traced to a particular part of the brain. For example, Freudian theory and the theory of the unconscious seems to have a great deal to offer and has been incorporated into our culture, but modern science has not been able to identify an “unconscious” part of the human brain. There are many mysteries of the human brain and psyche that have not been explained fully and may never be.

BILATERAL BRAIN THEORY