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 tumors, abscesses (pockets of pus), and disorders that cause progressive degeneration of certain areas of the brain, such as Alzheimer disease.
Agnosia symptoms vary depending on the lobe that is damaged:
Parietal lobe: This type of damage usually results from a stroke. 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) or places (called environmental agnosia).
Temporal lobe: People may be unable to recognize sounds even though they can hear sounds. This impairment is called auditory agnosia.
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:
Most recovery occurs within the first 3 months, but people may continue to improve to some degree for up to a year.
When possible, the cause 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.