Before modern research techniques and equipment were available, the only way to study cerebral lateralization was to study people with damaged brains. The damage might occur due to injury or disease. In the 1860s, researcher Pierre Broca found that damage in the left hemisphere caused the inability to form words, a condition called nonfluent aphasia.
Karl Wernicke later observed that if a different area in the left hemisphere was injured, a person could form words well but his speech was incomprehensible, a condition known as fluent aphasia. These observations resulted in the theory that language is produced and analyzed in the left hemisphere. Later research shows that language, especially in women, is sometimes governed by both hemispheres.