In the 1950's, it was discovered by Sperry that seriously ill epileptic patients could be treated by separating the two hemispheres of the brain with an incision. Sperry went on to reveal that each of these apparently normal patient's two hemispheres were able to function in complete autonomy. The left side being active in speech and the right side in shape recognition. This fundamental discovery gave rise to a multitude of extrapolations concerning the "right brain" and the "left brain". In this book, Gazzaniga, who has expanded on Sperry's research, put things into perspective and shows us that it is more complex than was previously thought. According to him, the brain is most certainly made up of relatively autonomous modules which react independantly to environmental pressures. At least one of the modules, situated on the left side of the brain, is responsible for the interpretation of answers which may be contradictory with others, whereas yet another module on the same side translates into words the result of this interpretation. So, instead of being a unique, monolithic system that we imagined, the brain would appear to be a collectivity of systems - a social brain. This approach enlightens us as to the functioning of the human brain, and according to Gazzaniga, affects the very roots of our belief systems and societies.

Renowned American neurologist, Michael Gazzaniga is Director of the Cognitive Neuroscience Division of Cornell University and chairman of Neuropsychology. He was once the student of Roger W. Sperry, who revolutionized neurology with his studies of the division of the human brain.