My Stroke of Insight: A Brain Scientist's Personal Journey Read Online Free PDF Page A

years. To my knowledge, the first person on record to suggest that each hemisphere actually had its own mind was Meinard Simon Du Pui. In 1780, Du Pui claimed that mankind was Homo Duplex - meaning that he had a double brain with a double mind. 10 Nearly a century later, in the late 1800s, Arthur Ladbroke Wigan witnessed the autopsy of a man who could walk, talk, read, write, and function like a normal man. Upon examination of his brain, however, Wigan discovered that this man had only one cerebral hemisphere. Wigan concluded that since this man, who had only "half" a brain, had a whole mind and could function like a whole man, then those of us who have two hemispheres must have two minds. Wigan enthusiastically championed this "Duality of the Mind" theory. 11
Over the centuries, various conclusions have been drawn about the differences and similarities in how the two hemispheres process information and learn new material. This subject gained tremendous popularity in the United States in the 1970s, following a series of split-brain experiments where Dr. Roger W. Sperry surgically cut the fibers of the corpus callosum of people experiencing severe epileptic seizures. In his 1981 Nobel lecture, Sperry commented:
Under the conditions of commissurotomy where background factors are equalized and where close left-right comparisons become possible within the same subject working the same problem, even slight lateral differences become significant. The same individual can be observed to employ consistently one or the other of two distinct forms of mental approach and strategy, much like two different people, depending on whether the left or right hemisphere is in use. 1
    Since those early studies of split-brain patients, neuroscientists have learned that the two hemispheres perform differently when they are connected to one another than when they are surgically separated. 2 When normally connected, the two hemispheres complement and enhance one another's abilities. When surgically separated, the two hemispheres function as two independent brains with unique personalities, often described as the Dr. Jekyll and Mr. Hyde phenomenon.
    Using noninvasive modern techniques including functional imaging (fMRI), scientists are now capable of visualizing which specific neurons are engaged in performing a designated function in real time. Because our two hemispheres are so neuronally integrated via the corpus callosum, virtually every cognitive behavior we exhibit involves activity in both hemispheres - they simply do it differently. As a result, the world of science supports the idea that the relationship between the two cerebral hemispheres is more appropriately viewed as two complementary halves of a whole rather than as two individual entities or identities.
It makes sense that having two cerebral hemispheres that process information in uniquely different ways would increase our brain's capacity to experience the world around us and increase our chances of survival as a species. Because our two hemispheres are so adept at weaving together a single seamless perception of the world, it is virtually impossible for us to consciously distinguish between what is going on in our left hemisphere versus our right hemisphere.
To begin, it is important to understand that hemispheric dominance is not to be confused with hand dominance. Dominance in the brain is determined by which hemisphere houses the ability to create and understand verbal language. Although the statistics vary depending upon whom you ask, virtually everyone who is right handed (over 85% of the U.S. population) is left hemisphere dominant. At the same time, over 60% of left handed people are also classified as left hemisphere dominant. Let's take a closer look at the asymmetries of the two hemispheres.
Our right hemisphere (which controls the left half of our body) functions like a parallel processor. Independent streams of information simultaneously burst into our brain via each of