Agnosia is loss of the ability to identify objects using one or more of the senses.
- Symptoms vary depending on where the brain is damaged.
- Doctors determine whether people have agnosia by asking them to identify common objects by sight, touch, or another sense and by doing a physical examination, tests of brain function, and imaging tests.
- The cause is treated if possible, and speech and occupational therapy may help.
Agnosia is relatively rare. Usually, only one sense is affected.
Agnosia is caused by damage to the parietal, temporal, or occipital lobe of the brain. These areas store memories of the uses and importance of familiar objects, sights, and sounds and integrate memory with perception and identification.
Agnosia often occurs suddenly after a head injury or stroke. Other causes of agnosia include brain tumors, brain abscesses (pockets of pus), and disorders that cause progressive degeneration of certain areas of the brain, such as Alzheimer disease.
Agnosia can involve any of the senses: hearing, taste, smell, touch, and sight.
Agnosia symptoms vary depending on the lobe that is damaged:
- Parietal lobe: People have difficulty identifying a familiar object (such as a key or safety pin) that is placed in the hand on the side of the body opposite the damage (called somatosensory agnosia). However, when they look at the object, they immediately recognize and can identify it. Some people with a damaged parietal lobe insist that nothing is wrong or ignore the problem, even when one side of their body is paralyzed (called anosognosia).
- Occipital lobe: People cannot recognize common objects, such as a spoon or a pencil, even though they can see these things. This impairment is called visual agnosia. They may not recognize familiar faces (called prosopagnosia).
- Temporal lobe: People may be unable to recognize sounds even though they can hear sounds. This impairment is called auditory agnosia.
- Occipital and temporal lobe: People may not recognize familiar places (called environmental agnosia). They may be color blind.
- A doctor's evaluation
- Standardized tests of brain function
- Imaging tests such as computed tomography or magnetic resonance imaging
Doctors ask the person to identify common objects by sight, touch, or another sense. Doctors also do a physical examination to determine whether symptoms are caused by another disorder such as an eye or a hearing disorder.
Certain standardized tests of brain function (neuropsychologic testing) may be done. These tests may involve questions and/or requests to do specific movements.
Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), are done to check for causes of brain damage, such as a tumor or stroke. Other tests may be done depending on the suspected cause.
How well a person recovers is influenced by the following:
- The type, size, and location of the damage
- The extent of the impairment (for example, how difficult recognizing objects is)
- The person's age
- The effectiveness of treatment
Most recovery occurs within the first 3 months, but people may continue to improve to some degree for up to a year.
- Treatment of the cause
- Speech and occupational therapy
When possible, the cause of agnosia is treated. For example, if an abscess is the cause, treatment may include antibiotics and surgery to drain the abscess.
No specific treatment for agnosia exists.
Speech and occupational therapy can help people with agnosia learn to compensate for their impairments.
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