Two Brains in One: The Hemispheres

As a result of a series of remarkable surgical experiments in the mid-1960s, neuroscientists discovered an astonishing fact about the brain’s hemispheres: they operate as two separate, independent computers, with two uniquely different ways of processing data. Surgeons Joseph E. Bogen and Philip J.Vogel, working at CalTech, began performing a controversial, last-resort surgical technique on patients suffering from severe epilepsy. They theorized that, by severing most of the corpus callosum, the thick band of nerve fibers that connect the two hemispheres, they could prevent epileptic seizures from spreading across the entire brain, or at least limit their severity. Most surgeons had previously believed that such an extreme insult to the brain’s structure would totally incapacitate the patient, or at the least seriously impair his or her general mental functions. But experiments by neuroscientists Roger Sperry and Ronald Myers with cats
and monkeys had indicated no observable impairment. As a result, Bogen and Vogel applied the procedure in a number of cases, with positive results for the epilepsy and no noticeable impairment in mental function. In addition to providing a last-resort treatment for intractable epilepsy, which was eventually rendered unnecessary by more effective drug treatments, the surgical transection of the corpus collosi produced a small population of very unusual human beings. They all had divided brains. Sperry, Myers, and their colleague Michael Gazzaniga performed a wide range of cognitive experiments with these special splitbrain people, over a number of years. Here’s what they discovered. In normal humans (not including the split-brain population), each hemisphere knows what the other hemisphere knows, as a result of the constant swapping of information across the corpus callosum. But each hemisphere “knows” in a different way. The left hemisphere, or “left brain” as pop-psychology fans like to call it, responds much more readily to certain aspects of the data stream than to others. Conversely, the “right brain” responds to its own preferred aspects of the data.Working together they get the job of thinking done, but each makes a different kind of contribution. The left hemisphere—let’s call it “LH”—is more attentive to elements of data—words, phrases, sentences, numbers, repetitive parts of patterns, procedures, sequences, time intervals, and logical “if-then” progressions of ideas. It specializes in noticing, reacting to, and thinking with the “bits and pieces” of information that flow through it. Logic, mathematics, and structure are the home territory of LH thinking. The right hemisphere—the “RH”—is more attentive and more skillful in processing patterns in the data.These include recognizing spatial forms and structures, colors, sound patterns such as musical melodies, and the patterns of intonation of speech.Your RH creates your subjective body image—your sense of your own physical structure, bodily boundaries, and the location and movement of your limbs in space, also known as proprioception. The RH also seems to be much more attentive to the social and emotional meanings of what it’s perceiving. And, of course, we typically associate the term intuition with the RH style of processing. To simplify and sloganize the differences for convenience: the LH specializes in “parts” and the RH specializes in “patterns.” In most normal people, the two hemispheres cooperate so closely that these profound differences are typically concealed. This probably explains why scientists only discovered the phenomenon of hemispheric lateralization in the 1960s when the split-brain surgeries lifted the veil on the brain’s exquisite integration and cerebral synergy. Consider the very ordinary experience of singing a song. Most likely, your RH would conjure up the melody and supply the cues for pitch, intonation, and phrasing, while your LH would retrieve the lyrics (the words). All of this information would flow to your vocal apparatus through the LH speech center, the parietal lobe’s motor center, and probably the cerebellum as well. It’s no wonder that most of us have to practice diligently to learn to sing competently. There’s a lot going on in your head when you sing. Since the discovery of brain lateralization, many scientists and many science popularizers have taken an interest in the implications of the discovery for personal growth and individual effectiveness. Unfortunately, myth and imagination have displaced science in some areas, and various popular myths have sprouted out of wishful thinking. For example,physiological studies indicate certain variations in brain structure and lateralization between males and females and different patterns of learning and competence during childhood. However, the interpretation of this domain of research is so burdened with socio-political controversy that it’s impossible to do it justice within the scope of this book. Consequently, I’ve cravenly elected to limit this discussion and to refer interested readers to the abundant research literature to be found on the Internet.