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A cognitive disorder marked by an impaired ability to comprehend or express language in its written or spoken form. This condition is caused by diseases which affect the language areas of the dominant hemisphere. Clinical features are used to classify the various subtypes of this condition. General categories include receptive, expressive, and mixed forms of aphasia.

Aphasia not dependent on a manifest cerebral lesion, but occurring as a congenital defect, in severe constitutional diseases, or as the result of emotional excitement in hysterical persons.