The diverse functions of our two brain hemispheres have been the subject of some of the most exciting research findings about human anatomy and behavior in the last sixty years. First identified in the late 1950s by Roger Sperry and Ronald Meyers, in experiments first with cats and then with monkeys, the data became important to consciousness study when it was applied to human subjects. In the 1960s, at the California College of Medicine (now the University of California at Irvine) and the California Institute of Technology, a group of severely epileptic patients underwent operations in which their brain hemispheres were surgically separated. The nerve fibers known as the corpus callosum, which joins the two halves of the brain and serves as the primary information pathway between the two, was severed in an attempt to keep seizures isolated to one hemisphere. (The hemispheres are still connected at the brainstem, however.) As a surgical and therapeutic technique it was effective. What was learned as a result of this intervention continues to have a profound impact on our knowledge of the human brain, particularly in the areas of perception, speech and language, and human learning and creativity.

The split-brain people," as they came to be known, acted quite normally, but exhibited some curious behaviors when subjected to certain tests. For instance, they were seated behind a screen that blocked their view of the objects on the table in front of them, then asked to identify an item placed in one hand. If a comb, for instance, was put in the right hand, it was recognized as such and verbally labeled. If, however, the comb was first placed in the left hand, the subject could indicate, through gesturing, how it might be used, and recognize it from among other items, but drew a blank when asked to name what it was.

The researchers concluded - and later studies verified - that the right hemisphere of the brain controls the left side of the body, and the left hemisphere controls the right side of the body. When the left hand was sending information about an object, the right hemisphere didn't have a word for it. With the object in the right hand, however, the left brain recognized it as comb and named it as such.

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