Impairment in the comprehension of speech and meaning of words, both spoken and written, and of the meanings conveyed by their grammatical relationships in sentences. It is caused by lesions that primarily affect Wernicke's area, which lies in the posterior perisylvian region of the temporal lobe of the dominant hemisphere. (From brain & Bannister, Clinical neurology, 7th ed, p141; Kandel et al., Principles of Neural science, 3d ed, p846)