Aphasia is a language disorder caused by damage to brain regions involved in language processing, most commonly from stroke affecting the left hemisphere. Different types of aphasia, corresponding to different lesion locations, produce distinctive patterns of language impairment that have been instrumental in mapping the neural architecture of language. Aphasia affects approximately one-third of stroke survivors and can impair speaking, understanding, reading, and writing while leaving other cognitive abilities relatively intact.
Major Types
Broca's aphasia (damage to the left inferior frontal gyrus and surrounding regions) produces nonfluent, effortful, telegraphic speech with relatively preserved comprehension. Patients omit function words and grammatical morphemes ("man...go...store"). Wernicke's aphasia (damage to the left posterior superior temporal gyrus) produces fluent but semantically empty speech with severely impaired comprehension. Patients speak in flowing sentences that lack meaningful content ("I went to the thing and got the thing for the thing"). Global aphasia (extensive left-hemisphere damage) impairs both production and comprehension.
Conduction aphasia
Conduction aphasia (damage to the arcuate fasciculus connecting Broca's and Wernicke's areas) produces relatively fluent speech and good comprehension but impaired repetition and frequent phonemic paraphasias (sound substitutions). Anomic aphasia (various lesion locations) produces word-finding difficulty as the primary symptom — patients know what they want to say but cannot retrieve the word.
Language recovery after aphasia depends on lesion size, location, time since onset, and the individual's premorbid language abilities. Some recovery occurs spontaneously in the first months, potentially through resolution of diaschisis (functional disruption in connected but undamaged areas). Further recovery can be promoted by speech-language therapy, which exploits neural plasticity to strengthen surviving language networks or recruit alternative pathways, including right-hemisphere homologues of left-hemisphere language areas.