What is a aphasia?
An aphasia is the loss of your ability to understand or express language. There are 6 types of aphasias, producing different patterns of language difficulties depending on where the damage has happened to the brain's language system. Four aphasia are typically caused by stroke of the middle cerebral artery (MCA), which supplies blood to the outside left and right sides (or lateral) parts of your brain. Specifically, this results in damage to key language brain areas and pathways connecting these key areas (called the arcuate fasiculus). For a description of these key brain areas, check out the "Language" page.
Types of Aphasia
The figure below demonstrates different symptom patterns, and their corresponding clinical name, depending on which brain regions in the language system are damaged. Fluent refers to the person's ability to produce language, like speaking and writing. Comprehension refers to the person's ability to understand language. Repetition refers to a person's ability to repeat the same exact thing that another person has said.
When Broca’s area (region primarily responsible for speech production) and the arcuate fasiculus are damaged, a person typically has mostly intact language comprehension, with slow, effortful speech production, and poor repetition.
When Wernicke’s area (the region primarily responsible for speech comprehension) and the arcuate fasiculus are damaged, the person has relatively intact and fluent production, with poor comprehension and repetition.
When there is only damage to the arcuate fasiculus, patients have relatively intact comprehension and production, but impaired repetition.
If there is widespread left hemisphere damage (impacting Broca’s area, Wernicke’s area, and the arcuate fasiculus), a patient will have poor language comprehension, production, and repetition.
Transcortical aphasias are usually due to damage to a watershed area, or a brain region supplied by 2 blood vessels. Typically, this damage occurs after not enough blood is supplied, called hypoprofusion. Because the arcuate fasiculus is not involved, there’s relatively intact repetition.
Transcortical Motor Aphasia
When there is damage to the watershed brain regions supplied by the anterior cerebral artery and middle cerebral artery, a patient will have impaired language production, but relatively intact comprehension.
When there is damage to the watershed brain regions supplied by the posterior cerebral artery and middle cerebral artery, a patient will have impaired language comprehension with relatively intact production.
Transcortical Sensory Aphasia
Thank you to Amanda M. Garcia, PhD for her expertise in helping compile this page!
 Catani, M., & Mesulam, M. (2008). The arcuate fasciculus and the disconnection theme in language and aphasia: history and current state. cortex, 44(8), 953-961.