The New York Review of Books

Nineteenth-century neurology was dominated by two opposing schools of thought. Early in the century the Austrian neuroanatomist Franz Gall and his disciples claimed that, to those practiced in the art, an examination of bumps on a person’s head revealed talents and psychological characteristics; traits of character, he held, were controlled by specific regions of the brain. Gall had a fashionable success in France, but was ridiculed by the leading neurologist of the day, M.J.P. Flourens, who had performed experiments on birds’ brains. At the height of his fame in the 1840s, when he defeated Victor Hugo for membership in the French Academy, Flourens believed that he had conclusively demonstrated that activities such as walking and flying were not dependent on any particular region of the brain. The brain functions as a whole, he argued, and it was impossible to predict the specific effects of any form of damage.

In 1861 the French neuroanatomist Paul Broca demonstrated that damage to a specific region on the left side of the cerebral cortex caused severe language problems, such as an inability to speak fluently. This was the first serious challenge to Flourens and the “holistic” school. Subsequently, the German neurologist Carl Wernicke found another region on the left side of the brain that apparently controlled different aspects of language, including the ability to understand speech. Wernicke argued that the region on the left side of the brain that had been discovered by Broca was somehow responsible for translating language formulated in the brain into the mechanical movements of the vocal cords, the tongue, and the mouth. A band of fibers called the arcuate fasciculus connected Broca’s region to the same region that Wernicke himself had discovered; and Wernicke believed that the region he had discovered was responsible for the recognition, or sorting, of speech as distinct from other sounds. Clinicians soon found that such “localization” of brain functions explained many other patterns of neurological disorders in addition to language. In 1884, for example, a patient with epilepsy and partial paralysis had a brain tumor removed in the first such operation in medical history. The neurological symptoms enabled the surgeon to locate the exact position of the tumor.

During the early years of the twentieth century, however, the belief that psychological behavior derived from separate mental faculties, each controlled by different centers in the brain, became increasingly unpopular; most neurologists and psychologists considered this an implausible view of human psychology. In 1927 a neurology textbook noted:

Neurologists have been prone, even up to the present time, to fall into the error of attempting to find specific centers for particular mental functions or faculties. But the evidence at present available gives small promise of success in the search for such centers. It is, in fact, theoretically improbable that such discoveries will ever be made, for psychology today recognizes no such mosaic of discrete mental faculties as would be implied by such a doctrine.

For many neurologists, the anatomical evidence also …