Aphasia is an impairment of language which occurs when someone suffers injury to the language areas of the brain. Aphasia can affect language in many ways including its production (ability to speak), and its comprehension (ability to understand others when they speak), as well as other related abilities such as reading and writing. Over 20% of all people who suffer a stroke develop some form of aphasia. The following are the three most common types of aphasia and their characteristics:
Broca's aphasia is at times called "motor aphasia" to emphasize that it is the production of language which is impaired, (such as speaking) while other aspects of language are mostly preserved. Typically, Broca's aphasia prevents a person from forming her own intelligible words or sentences, but leaves her with an ability to understand others when they speak. Often, people with Broca's aphasia are frustrated because they can't transform their thoughts into words. Some aphasics can say a few words which they use to communicate in a characteristic type of speech known as telegraphic speech.
People with Wernicke's aphasia can't understand others, or even themselves, when they speak. Their speech, however, is incomprehensible, as they create sentences whose words are arranged in an apparently random and often amusing fashion. When people with Wernicke's aphasia speak, they feel as though they are being understood. This is caused by their lack of awareness of their profound language impairment, (anosagnosia). Over time, Wernicke's aphasics might learn that others can't understand them when they speak, so they might become angry, paranoid, and depressed.
This is the type of aphasia that results when damage in the brain is extensive enough to involve both the Broca's and Wernicke's language areas. People with global aphasia are unable to understand spoken language, or to speak. In some cases, however, people with global aphasias can still communicate by using written language.