A condition, caused by neurological damage or disease, in which a person’s previous capacity to understand or express language is impaired. The ability to speak, listen, read, or write may be affected depending on the type of aphasia involved.
In contrast to neurological problems that affect the physical ability to speak or perform other linguistic functions, aphasia involves the mental ability to manipulate speech sounds, vocabulary, grammar, and meaning. There are several different types of aphasia. Each has different symptoms and is caused by damage to a different part of the brain.
The great majority of aphasias are caused by damage to the left hemisphere of the brain, which is the dominant language hemisphere for approximately 95 percent of right-handed people and 60 to 70 percent of left-handed people. Two areas in the left hemisphere—Broca’s area and Wernicke’s area—and the pathways connecting them are especially important to linguistic ability, and damage to these areas is the most common cause of aphasia. Broca’s area, located in the frontal lobe of the left hemisphere, is named for the 19th-century French physician Paul Broca (1824-1880), an early pioneer in the study of lateralization (the specialized functioning of the right and left sides of the brain). Aphasia resulting from damage to this area, called Broca’s aphasia, is characterized by slow, labored, “telegraphic” speech, from which common grammatical function words, such as prepositions and articles, are missing (“I went doctor”). In general, however, comprehension of spoken and written language is relatively unaffected.