Merck Manual

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Juebin Huang

, MD, PhD, Department of Neurology, University of Mississippi Medical Center

Reviewed/Revised Aug 2023
Topic Resources

Aphasia is partial or complete loss of the ability to express or understand spoken or written language. It results from damage to the areas of the brain that control language.

  • People may have difficulty reading, writing, speaking, understanding, or repeating language.

  • Doctors can usually identify the problem by asking the person questions.

  • Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), are done.

  • Speech therapy can help many people with aphasia.

In right-handed people and about two thirds of left-handed people, language function is controlled by the left half of brain (left cerebral hemisphere). In the other third of left-handed people, much of language function is controlled by the right half. Thus, in most people, language function is controlled by the following areas of the brain:

  • Part of the left frontal lobe called Broca area

  • Part of the left temporal lobe called Wernicke area

  • The lower back part of the left parietal lobe (next to the Wernicke area)

  • The connections between these areas

Damage to any part of these areas interferes with at least some aspect of language function. Usually, writing and speech are affected similarly.

Causes of Aphasia

Aphasia usually results from disorders that do not cause progressive damage, such as the following:

In such cases, aphasia does not continue to worsen over time.

But if it results from a progressive disorder (such as an enlarging brain tumor), aphasia can progressively worsen. As the tumor gets bigger, it may put more pressure on areas of the brain that control language function and further impair the ability to express or understand language. Some types of dementia can also cause aphasia that progressively worsens.

People with aphasia have difficulty expressing or understanding language. But the nature and degree of the difficulty vary. The variety reflects the complex nature of language function.

Types of Aphasia

There are two main types of aphasia:

  • Wernicke (receptive) aphasia: If the Wernicke area is damaged, people have difficulty understanding spoken and written language. They usually speak fluently and with a natural rhythm, but the sentences come out as confused strings of words (sometimes referred to as word salad). They may not know that they are speaking nonsense. Most affected people are also unable to read words. They write as they speak—fluently but incomprehensibly.

  • Broca (expressive) aphasia: If the Broca area is damaged, people may mostly understand the meaning of words and know how they want to respond. However, they have difficulty finding the words to say. Their words are forced out slowly and with great effort, sometimes interrupted by expletives, but what they say makes sense to them. The normal rhythm and emphasis of speech is also missing. They have trouble repeating phrases. Most affected people are also unable to write words.

When Specific Areas of the Brain Are Damaged

Different areas of the brain control specific functions. Consequently, where the brain is damaged determines which function is lost.

When Specific Areas of the Brain Are Damaged

Aphasia may also involve

  • Loss of the ability to comprehend written words (alexia)

  • Loss of the ability to recall or say the names of objects (anomia): Some people with anomia cannot remember the right word at all. Others have a word in mind but cannot say it. People with anomia tend to speak fluently but use phrases that do not mean anything or say what they mean in a round-about way. Most people with aphasia have anomia. This type of aphasia is called anomic aphasia.

  • Loss of the ability to repeat words, phrases, or sentences (conduction aphasia): People with conduction aphasia cannot repeat what they hear. They often use the wrong word or use word combinations that do not make sense. They can speak fluently, but they cannot say the names of objects (anomia).

  • Loss of almost all ability to understand, speak, or write language (global aphasia): Global aphasia occurs when the left temporal and frontal lobes (including the Broca and Wernicke areas) are damaged. People may be able to utter expletives because the right side of the brain, which is more involved in emotions, is not damaged.

Most people with aphasia have more than one type, although one type is often more severe than the others. Most people who have expressive or receptive aphasia have both types to some degree. But types of aphasia overlap a lot. Thus, doctors tend to describe the specific problems a person has in addition to identifying the type of aphasia.

Diagnosis of Aphasia

  • A doctor's evaluation

  • Standardized tests of brain function

  • Imaging tests such as computed tomography or magnetic resonance imaging

Usually, doctors can identify aphasia by talking with the person and asking a few questions. However, they need to make sure that the apparent problems with language are not caused by problems with hearing or vision or by muscle or nerve problems that affect speaking or writing, including dysarthria. Dysarthria Dysarthria Dysarthria is loss of the ability to articulate words normally. Speech may be jerky, staccato, breathy, irregular, imprecise, or monotonous, but people can understand language and use it correctly... read more is a speech problem, which is due to damage that affects the nerves and muscles that control the ability to speak—the ability to physically pronounce sounds and words. Aphasia is a language disorder, indicating a brain problem that affects comprehension, thought, and word finding.

Doctors evaluate how fluently people speak, whether starting to speak is difficult, and whether people have difficulty finding words, naming objects, or repeating phrases. Doctors also check how well people understand what is said to them—for example, whether they can understand and carry out a command. People are asked to write and to read aloud.


Certain standardized tests of brain function (neuropsychologic testing Diagnosis ) may be given by a neuropsychologist or speech and language therapist. Neuropsychologic testing provides information about how different areas of the brain are functioning. These tests can help doctors identify aphasia that causes only subtle symptoms. These tests also help doctors plan treatment and determine how likely recovery is.

Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), are done to find out what type of brain damage caused the aphasia. Other tests may be done depending on the suspected cause.

Treatment of Aphasia

  • Treatment of the cause

  • Speech therapy

  • Use of communication devices

Treating certain causes of aphasia can be very effective. For example, if a tumor causes swelling in the brain, corticosteroids can reduce the swelling and improve language function. Aphasia due to some other causes (such as a stroke) may lessen more slowly or only partially when the cause is treated.

Speech therapists Aphasia can help people who develop aphasia after brain damage due to disorders that do not cause progressive damage. Therapy is usually started as soon as people are able to participate. The sooner therapy is started, the more effective it is, but it is helpful even when started late.

If people with aphasia do not recover basic language skills, they may be able to communicate using a book or a communication device, such as a board with pictures or symbols of often-used words or daily activities or a computer-based device with a keyboard and message display.

Family members and other people who care for a person with aphasia can become frustrated. Remembering that aphasia is a physical disorder and that a person has little control over it can help.

Prognosis for Aphasia

How well a person recovers is influenced by the following:

  • The cause, size, and location of the damage

  • The extent that language is impaired

  • The response to treatment

  • To a lesser degree, the age, education, and general health of the person

Children under 8 years old often regain the ability to use language, even when the brain has been severely damaged. For people older than 8 years, most recovery occurs within the first 3 months, but they may continue to improve to some degree for up to a year.

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