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Agnosia is loss of the ability to identify objects using one or more of the senses.
Agnosia is relatively rare. 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. Usually, only one sense is affected.
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 insist that nothing is wrong or ignore the problem, even when one side of their body is paralyzed.
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 environment 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. Other tests may be done depending on the suspected cause.
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