Scientists today are using the latest imaging technologies to investigate Sigmund Freud's most fundamental tenets: that dreams represent unfulfilled wishes, that the three parts of the psyche--the ego, id and superego--have neuronal bases, and that "talk therapy" changes the physical networks of neurons in the brain. The fact that such work is happening at all represents an apparent comeback for psychoanalysis [see "Freud Returns," by Mark Solms, on page 28]. No one would be happier than Freud himself. Although his followers like to think of his work as pure psychology, the young Freud built his theories on his own detailed investigation of animal and human brains. To him, every mental illness stemmed from a physical defect in the brain.