Medicine has charted much of the human body's intricate terrain, but the brain still remains an elusive frontier. In popular science books, most neurologists reason their way through the region in one of two ways: inductively (humanists such as Oliver Sacks who consider psychology and philosophy and reach largely intuitive conclusions) and deductively (cognitive scientists, such as Cornell's Michael Gazzaniga, who fit the evidence into frameworks based on hard science). Gazzaniga's is one of the most intricate empirically-based theories and yet he explains it with clarity and wit.
At any moment, Gazzaniga posits, thousands, perhaps millions, of "modules" cause mood shifts without being part of our conscious experience. Once the emotional changes are experienced, a left brain "interpreter" takes note and attempts to the find reasonable explanation for the module's actions. Gazzaniga's interpreter (which resembles Freud's ego or Descartes' soul) then builds up a memory of explanations. When the interpreter mistakenly pairs up cause-and-effect (often because of chemical imbalances in the brain), anything from insomnia to psychosis can result.
In an unfortunate digression toward the book's end, Gazzaniga extends his theory to society, criticizing the view that government has an obligation to the poor. If the interpreter of a poor person observes that money can be gained without working, Gazzaniga posits, it will find it unnecessary to earn a living. If anything, though, Gazzaniga's theory shows how poverty can cause the interpreter to reach erroneous conclusions about self-worth. Nevertheless, while these arguments obviously will be debated for some time, most of Gazzaniga's theories are rigorously constructed and compelling for their ability to explain a wide range of neurological behavior.