In normal human adults, each hemisphere of the brain,working in concert with the other, performs certain types of functions more efficiently than the other. While the left-brain hemisphere is dominant in the areas of language and logic, the right-brain hemisphere is the center of nonverbal, intuitive, holistic modes of thinking. Each hemisphere mostly receives perceptions from and controls the activities of the opposite side of the body.
Scientists have been aware of the specialized functioning of the hemispheres—also known as lateralization—for over one hundred years, having discovered that language skills are controlled by the left side of the brain in approximately 95 percent of right-handed people and about two thirds of left-handed individuals.
In the nineteenth century, however, this discovery led to the assumption that all higher reasoning ability resided in the left-brain hemisphere, which was thus regarded as dominant overall. The right brain hemisphere was thought to possess only lower-level capabilities and was considered subordinate to the left.
Research conducted in the 1950s and 1960s established that the two hemispheres of a normally functioning brain—connected by the corpus callosum, a thick cable of nerves—operate in a complementary fashion with both hemispheres involved in higher cognitive functioning.
The primary difference between them was found to involve the mode rather than the level of thinking. A research group under the direction of Roger Sperry at the California Institute of Technology observed and tested patients who had undergone a surgical procedure in which the corpus callosumwas severed to control epileptic seizures.
In this procedure, the two hemispheres of the brain, which normally have a strong tendency to work together, were uncoupled, and each side of the brain remained ignorant of information received by the other. Thus, right-handed people had no trouble writing, which is usually governed by the left-brain hemisphere in righthanders, but were unable to draw, as the left brain was cut off from the spatial capacity of the right.
When a special apparatus was used to present the image of a spoon only to a split-brain patient’s left hemisphere, the subject could name it readily, but when the same image was presented to the right-brain hemisphere, the subject could not, although they were still aware of what it was.
Research on both split-brain and normal subjects since the 1960s has confirmed that both hemispheres of the brain use high-level cognitive modes. That of the left brain is verbal and analytic, while right brain thought processes are rapid, complex, whole-pattern, spatial, and specialized for visualimagery and musical ability.
The right temporal lobe, in particular, governs visual and auditory imagery. People in whom this area is damaged have difficulty recognizing familiar melodies, faces, and pictures, and learning to identify new ones. The right brain hemisphere also appears to have special links to emotion.
Right-brain damage interferes with both the ability to produce and interpret expressions of emotion. Damage to the front part of the right-brain hemisphere renders people unable to act on or express strong emotions. If the damage is further back in the brain, the person can express emotion but not recognize it in other people or in pictures.
Other general characteristics of right-brain thought processes include the tendency to synthesize rather than analyze, and to relate to things in a concrete rather than a symbolic fashion. Where left-brain thinking tends to represent wholes by abstraction (using one piece of information to represent something larger), the right brain is more likely to interpret data through analogies ó —seeing relationships between wholes.
Right-brain functioning is nontemporal, nonrational, holistic, and intuitive, relying on leaps of insight, hunches, or visual images. Discoveries about the right- and left-brain hemispheres have led some researchers and educators to advocate educational reforms that would allow right-brain modes of thought a greater place in the current educational system, which reflects society’s overall tendency to reward the verbal, analytical left-brain skills.
As split-brain researcher Roger Sperry notes, our educational system “tends to neglect the nonverbal form of intellect. What it comes down to is that modern society discriminates against the right hemisphere.” The artistic, creative right brain is relegated to the “minor” subjects of art and music, but the main programs of study do not, as a rule, focus on developing the right-brain skills of imagination, creativity, or visualization.