A condition, caused by neurological damage or disease, in which a person's previous capacity to understand or express language is impaired. The ability to speak, listen, read, or write may be affected depending on the type of aphasia involved.

In contrast to neurological problems that affect the physical ability to speak or perform other linguistic functions, aphasia involves the mental ability to manipulate speech sounds, vocabulary, grammar, and meaning. There are several different types of aphasia. Each has different symptoms and is caused by damage to a different part of the brain.

The great majority of aphasias are caused by damage to the left hemisphere of the brain, which is the dominant

language hemisphere for approximately 95 percent...