The idea that specific mental processes are located in, or associated with, discrete parts of the brain can be traced back to the early 1800s when a German physician Franz Gall invented phrenology. Its most important assumption was that bumps on the skull could reveal our mental abilities and character traits.
As Raymond Fancher explains, Gall was the first great comparative anatomist of brains. His careful examination of the brains of many different species led him to the conclusion that higher mental functions correlated with the size of the brain. While the correlation is imperfect, he did demonstrate the tendency for animals with larger brains to manifest more complex, flexible, and intelligent behavior. It was this demonstration, more than any other argument, that convinced scientists that the brain was the center of all higher mental activity.
Unfortunately, because Gall embedded this contribution in the ill-fated theory of phrenology, he is now viewed as somewhat of a quack. Gall's theory appears to have had its origin in an early childhood experience. In his autobiography he relates how as a boy he was exasperated by fellow students who, while less intelligent than himself, received higher grades because they were better memorizers. In reflecting on his rivals, he concluded that they all had one prominent physical characteristic in common: large and protruding eyeballs. Convinced that greater intelligence was associated with larger brains, he speculated that specific parts of the brain were the seats of specific faculties or traits. People with good verbal memories might have particularly well-developed "organs of verbal memory" somewhere in their brains. Gall further surmised that this was in the region of the frontal lobes directly behind the eyes, where the pressure of the enlarged brain caused the eyes to protrude.
By observing people who exhibited particular characteristics, Gall pinpointed areas of the brain responsible for 37 different traits, including musical talent, cautiousness, faithfulness, benevolence, and hope. For example, when he asked a group of lower-class boys that he had befriended to run errands for him, he found that their attitudes toward petty theft varied greatly. Measuring the boys' heads, he reported that the inveterate thieves had bumps just above and in front of their ears. He hypothesized an "organ of acquisitiveness" in the brain beneath. Observation of people with strong sexual drives convinced Gall that they had well-developed neck and skull bases. This led him to localize the personality characteristic of "amativeness" in the cerebellum.
At the height of its popularity, phrenology was a parlor game played by the well-to-do in Europe. It found particularly fertile soil in the United States, where celebrities such as Edgar Allan Poe and Walt Whitman were among its adherents. Manuals for self-diagnosis were published. Phrenologists even counseled employers on screening job applicants. In 1852, Horace Greeley suggested that railroad workers be selected by the shape of their heads. Phrenology proved influential until well into the twentieth century.
Fancher suggests that among the obvious weaknesses of Gall's theory were (1) his assumption that the shape of the skull accurately reflected the shape of the brain, (2) his totally inadequate classification of psychological characteristics that immediately doomed any attempt to localize these in the brain, and (3) his selective and arbitrary methods of observation. With three dozen interacting traits to work with, it became easy to rationalize any apparent discrepancies in the theory. Presented with a huge organ of acquisitiveness in a generous person, Gall could argue that a larger organ of benevolence counteracted the acquisitive tendencies. Or, certain organs might temporarily be impaired by disease. In short, the theory could not be falsified. Some of Gall's students dramatically demonstrated this pitfall. When a cast of Napoleon's right skull predicted qualities at variance with his known personality, one phrenologist replied that his left side had been dominant, but a cast of it was (conveniently) missing. When Descartes' skull was found deficient in the regions for reason and reflection, phrenologists argued that the philosopher's rationality had always been overrated. Although it's easy to find Gall's notions ridiculous, as Bryan Kolb notes, we are well reminded of how even now we use physical appearance to judge personality traits. For example, the current research literature points to the presence of a strong physical-attractiveness stereotype in which we judge what is beautiful as good.
For students who want to learn more about phrenology, you might send them to http://pages.britishlibrary.net/phrenology. The site includes information on the history of phrenology as well as a detailed map of the skull, linking brain regions with specific functions.
Fancher, R. (1996). Pioneers of psychology (3rd ed.). New York: Norton. Kolb, B., & Whishaw, I. (2003). Fundamentals of human neuropsychology (5th ed.). New York: Worth.