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 Overview of Head Injuries Head injuries that involve the brain are particularly concerning. Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities... read more or stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more . Other causes of agnosia include brain tumors Overview of Brain Tumors A brain tumor can be a noncancerous (benign) or cancerous (malignant) growth in the brain. It may originate in the brain or have spread (metastasized) to the brain from another part of the body... read more , brain abscesses Abscess of the Brain A brain abscess is a pocket of pus in the brain. An abscess may form in the brain when bacteria from an infection elsewhere in the head or in the bloodstream or from a wound enter the brain... read more (pockets of pus), and disorders that cause progressive degeneration of certain areas of the brain, such as Alzheimer disease Alzheimer Disease Alzheimer disease is a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells, the accumulation of an abnormal protein called beta-amyloid... read more .
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 The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods... read more .
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 The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods... read more .
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 The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods... read more .
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.
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.
How well a person recovers is influenced by the following:
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.
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.