"A debate on Cartesian dualism has led to radically differing approaches to the treatment of depression." A new book reveals how much is at stake in our understanding of the mind. "If consciousness and all its manifestations were 'merely' the firing of neurons and the release of chemicals in the brain, what need was there to focus on mental states? Once the physical brain was right, the rest would follow. It was an approach that has spawned a vast pharmaceutical industry to treat any pathological psychological state—anxiety, shyness, depression, psychosis—with a variety of pills."