Abstract

The first major advances in the understanding of the neurological bases for language abilities were the results of the study of the brains and behaviors of patients with language impairments due to focal brain damage. The two most prominent pioneers in this field are remembered because their names have become associated with distinctive aphasia (language loss) syndromes and the brain regions associated with them. In 1861 Paul Broca described the damage site in the brain of a patient who had lost the ability to produce articulate speech as a result of a stroke. Broca's aphasia, as it is now commonly called, is produced by damage that involves the inferior left frontal lobe of the brain. It tends to produce both a loss of articulatory skill (sometimes but not always with paralysis) and (as discovered much later) problems with grammar and syntax, including grammatical comprehension under certain conditions. Despite speech production impairments, Broca's aphasics do not have basic word‐ and sentence‐comprehension difficulties, when comprehension is not dependent on syntactic analysis. In 1874 Carl Wernicke demonstrated that damage to the left superior temporal lobe produced a different syndrome of language impairments. Wernicke's aphasia generally spares fluent, syntactic speech but impairs the use and comprehension of content words. Wernicke's aphasics'speech includes inappropriate word substitutions, neologisms, and semantic confusions, and their comprehension is similarly disturbed. These early studies also demonstrated that these aphasic disturbances were almost exclusively associated with damage to the structures of the left cerebral hemisphere, even though anatomically corresponding structures are present on both sides of the brain. However, this is not true of all language functions. Some left‐handed individuals can suffer aphasia from right hemisphere damage, and recent studies of patients with right hemisphere damage without aphasia have demonstrated impairment of their comprehension above the sentence level (e.g., interpretation of jokes and stories) and in the production and interpretation of prosodic features of speech (rhythmic and tonal patterning that conveys emphasis and emotion).