The Consciousness Instinct: Unraveling the Mystery of How the Brain Makes the Mind by Michael S. Gazzaniga; Farrar, Straus and Giroux, 288 pp., $28
In his engaging and wide-ranging new book, The Consciousness Instinct, neuroscientist Michael S. Gazzaniga explores a conundrum that has long baffled scientists: “Gazillions of electrical, chemical, and hormonal processes occur in our brain every moment, yet we experience everything as a smoothly running unified whole,” he writes. “What is the organization of our brain that generates conscious unity?”
Gazzaniga, director of the SAGE Center for the Study of the Mind at the University of California, Santa Barbara, and the author of numerous books on the brain, leads us through three possible approaches to answering this question. The first, and the one to which he devotes the most attention, is the modular theory of brain functioning. It holds that the brain, rather than operating in a holistic fashion, relies instead on thousands of independent processing units, or modules—localized neuronal networks that serve a specific function.
The inner workings of these networks are often revealed when people sustain brain damage to a specific area, allowing scientists to identify the module responsible for normal processing in a particular domain. Patients who suffer damage to the parietal lobe on the right side of the brain, for instance, experience spatial neglect: everything on the left side is ignored, almost as if it didn’t exist. They will not eat food on the left side of a plate, or shave or apply makeup to the left side of the face. Some even go so far as to deny the existence of a left arm or leg. This strange behavior, fully described in the 1950s, provided early evidence that the parietal lobe on the brain’s right side is responsible for bodily and spatial orientation.