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.
Causes of Agnosia
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.
Symptoms of Agnosia
Symptoms of agnosia vary based on which areas of the brain are damaged.
Agnosia can involve any of the senses:
Hearing (auditory agnosia): People cannot identify objects based on sound. For example, they cannot identify a telephone when they hear it ring. This type of agnosia results from damage to the temporal lobe.
Taste (gustatory agnosia): People cannot identify tastes even though they can experience them. This type results from damage to the temporal lobe.
Smell (olfactory agnosia): As in gustatory agnosia, people cannot identify odors even though they can experience them. Olfactory agnosia may result from damage to the front part of the temporal lobe.
Touch (somatosensory agnosia): For example, people have difficulty identifying a familiar object (such as a key or safety pin) that is placed in their hand. However, when they look at the object, they immediately recognize and can identify it. This type of agnosia results from damage to the parietal lobe.
Sight (visual agnosia): People cannot recognize common objects (such as a spoon or a pencil) even though they can see these things, but they recognize them when they touch the objects. Visual agnosia results from damage to the occipital lobe.
Typically, only one sense is affected.
In some types of agnosia, only specific processes within a sense are affected. They include the following:
Prosopagnosia: People cannot recognize familiar faces.
Environmental agnosia: People cannot recognize familiar places.
Achromatopsia: People become color blind.
Anosognosia: People insist that nothing is wrong or ignore the problem, even when one side of their body is paralyzed.
Simultanagnosia: People cannot see more than one object or part of an object at a time. If they look at a table with food and various utensils on it, they may say they see only a spoon.
Diagnosis of Agnosia
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 (called neuropsychologic testing) may be done. Standardized means that the tests are given in the same way to all people and scored the same way each time. Scores are then compared with those of healthy people with a similar background. The tests thus provide information about how different areas of the brain are functioning. Doctors ask people questions designed to evaluate intelligence, the ability to solve problems and to plan and initiate actions (called executive function), attention, memory, language, motivation, mood and emotion, quality of life, and personality.
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. For example, functional MRI (fMRI) can show which areas of the brain are active when a person does a specific task, such as reading, writing, remembering, calculating, or moving a limb. Positron emission tomography (PET) can show how active different areas of the brain are. However, these two tests are used mainly in research centers.
Treatment of Agnosia
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. These therapists help people with agnosias improve their communication skills by teaching them ways to stay oriented, maintain attention, recognize objects, plan the steps in carrying out tasks, solve everyday problems, and interact more effectively with other people.
Prognosis for Agnosia
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
If the cause of the damage can be reversed, most people start to recover during the first 3 months, and they may continue to improve to some degree for up to a year.
