When a patient has aphasia, they have sustained damage to the language areas of the brain, causing problems with reading, speaking, writing and/or listening. For the majority of people who are right-handed and around half of people who are left-handed, aphasia results from damage to the left side of the brain, according to the American Speech-Language-Hearing Association. Patients may develop aphasia after a head injury, tumor or stroke. The National Aphasia Association stated that the most common cause is a stroke, with 25 to 40 percent of survivors having the language disorder. In total, the National Institute of Neurological Disorders and Stroke (NINDS) estimated that in the United States, around 1 million people have aphasia.
Several types of aphasia exist, which differ based on the area of the brain that becomes damaged. The National Institute on Deafness and Other Communication Disorders (NIDCD) divided the types of aphasia into two broad categories: fluent aphasia and non-fluent aphasia. If a patient has fluent aphasia, the damage occurred in Wernicke's area of the brain, while a patient with non-fluent has damage to Broca's area (The NIDCD has a figure showing these regions of the brain on their aphasia page). Fluent aphasia is also called Wernicke's aphasia and non-fluent aphasia also goes by Broca's aphasia. A fluent aphasia patient speaks in long sentences that do not make sense or uses incorrect words. MayoClinic.com pointed out that a patient with fluent aphasia will have issues understanding spoken language; in addition, a fluent aphasia patient may not realize that people around her do not understand what she is saying. With non-fluent aphasia, the patient leaves out words when speaking and has trouble getting words out. The NIDCD added that a non-fluent aphasia patient speaks in short sentences, but other people can understand them.
Another type of aphasia is global aphasia, which the NIDCD defined as a non-fluent aphasia. A patient with this type of aphasia has very severe neurological damage. Both comprehension and expression abilities become affected.