Aphasia is an inability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke or head trauma. Aphasia can also be the result of brain tumors, brain infections, or neurodegenerative diseases, but the latter are far less prevalent.
To be diagnosed with aphasia, a person’s speech or language must be significantly impaired in one (or more) of the four aspects of communication following acquired brain injury.
Alternately, in the case of progressive aphasia, it must have significantly declined over a short period of time. The four aspects of communication are auditory comprehension, verbal expression, reading and writing, and functional communication.
The difficulties of people with aphasia can range from occasional trouble finding words, to losing the ability to speak, read, or write; intelligence, however, is unaffected. Expressive language and receptive language can both be affected as well.
Aphasia also affects visual language such as sign language. In contrast, the use of formulaic expressions in everyday communication is often preserved.
For example, while a person with aphasia, particularly expressive aphasia (Broca’s aphasia), may not be able to ask a loved one when their birthday is, they may still be able to sing “Happy Birthday”. One prevalent deficit in the aphasias is anomia, which is a difficulty in finding the correct word.
With aphasia, one or more modes of communication in the brain have been damaged and are therefore functioning incorrectly.
Aphasia is not caused by damage to the brain that results in motor or sensory deficits, which produces abnormal speech; that is, aphasia is not related to the mechanics of speech but rather the individual’s language cognition (although a person can have both problems, particularly if they suffered a hemorrhage that damaged a large area of the brain).
An individual’s “language” is the socially shared set of rules, as well as the thought processes that go behind verbalized speech. It is not a result of a more peripheral motor or sensory difficulty, such as paralysis affecting the speech muscles or a general hearing impairment.
While aphasia has traditionally been described in terms of language deficits, there is increasing evidence that many people with aphasia commonly experience co-occurring non-linguistic cognitive deficits in areas such as attention, memory, executive functions and learning.
By some accounts, cognitive deficits, such as attention and working memory constitute the underlying cause of language impairment in people with aphasia.
Others suggest that cognitive deficits often co-occur but are comparable to cognitive deficits in stroke patients without aphasia and reflect general brain dysfunction following injury.
Research is currently being done using functional magnetic resonance imaging to witness the difference in how language is processed in normal brains vs aphasic brains. This will help researchers to understand exactly what the brain must go through in order to recover from Traumatic Brain Injury and how different areas of the brain respond after such an injury.