aphasia

General term for the many types of disturbance in language that are due to brain damage, especially in the speech areas of the dominant hemisphere.

Classification systems are based on which part of the brain is thought to be affected or on which sensory or motor functions are impaired or language skills lost. The main types are: Broca's aphasia – patient's speech and writing severly affected but with full understanding of spoken and written language; Wernicke's aphasia – speech and writing affected in expression (errors in grammar, wrong and nonexistent words produced) and comprehension; conduction aphasia – lesion in the arcuate fasciculus, the pathway connecting Wernicke's area with Broca's, resulting in speech that is semantically abnormal, and difficulty in repeating sentences and reading aloud; aphasia due to lesions in the angular gyrus (a ridge on the side and towards the rear of the cortex) – difficulty in understanding spoken and written language and in naming objects; global aphasia – all language skills affected, presumably owing to lesions in both Broca's and Wernicke's area.