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What Is Agnosia?

Medically Reviewed by Dan Brennan, MD on May 18, 2021

Agnosia is a very rare disorder that causes you to lose the ability to recognize objects or people. Agnosia is often a result of damage to specific areas in the brain. You may still have your normal thinking ability in other areas because it usually only affects one information pathway.

What Causes Agnosia?

Agnosia can be caused by anything that can cause damage or degeneration to your brain. You may develop agnosia if the damage occurs in the part of your brain that links your memories to your senses and perception. These areas can be located in the parietal, temporal, or occipital lobes of the brain

Here are the common causes of this condition.

Ischemic stroke. This type of stroke happens when a blood vessel that supplies blood to your brain is blocked.

Brain tumor. This is a mass of abnormal cells in your brain. They can be cancerous or non-cancerous. Even non-cancerous tumors can cause problems with your brain function.

Brain abscess. This is a pocket of pus in your brain. It's caused by a bacterial or fungal infection. Abscesses can develop after trauma, infection, or surgery.

Traumatic brain injury. This occurs when there is damage to your brain from a violent hit or jolt to the head. Traumatic brain injury happens whenever anything pierces your skull and goes into your brain tissue.

Alzheimer's disease.Alzheimer's disease is a brain disorder that gets worse over time. It causes an abnormal build-up of protein in your brain that damages your brain cells.

Parkinson's disease dementia.Parkinson's disease can lead to Parkinson's disease dementia. It is caused by abnormal protein deposits in your brain. 

Types of Agnosia

Agnosia can have different symptoms depending on where the damage is located. It may involve any of your senses. But usually, only one is involved. Some forms of agnosia cause very specific and complex symptoms involving one sense.

Auditory agnosia. This affects your sense of hearing. You may not recognize a sound like a telephone ringing if you have this type of agnosia. But you can hear it.

Olfactory agnosia. This affects your sense of smell. You can still smell. You just can't identify what you're smelling.  

Visual agnosia. You can see common objects such as a spoon with this type of agnosia but you don't know what they are. You recognize them when you touch them. 

Gustatory agnosia. This affects your sense of taste. You don't recognize the taste when you taste something.  

Somatosensory agnosia. This is agnosia that affects your sense of touch. You can't recognize something familiar like a key by touch without looking at it. When you look at it, you can recognize it.  

Prosopagnosia. This is also called face blindness. If you have prosopagnosia you may have trouble identifying familiar faces. Prosopagnosia symptoms can also be more severe. They may prevent you from being able to tell unfamiliar faces apart. You may not be able to tell a face from an object or recognize your own face in serious cases.

Environmental agnosia. This is the inability to recognize familiar places such as your home or neighborhood. 

‌Achromatopsia. This is partial or complete color blindness. 

Simultanagnosia. You can't see more than one object or part of an object at a time. If you look at a table with a plate, glass, and spoon on it, you may only see the spoon. If someone points out the glass you may see the glass but no longer see the spoon.  

How Is Agnosia Diagnosed?

Your doctor will listen to your symptoms and do a physical exam. They may do tests to see if you can identify objects with your senses. You may need brain imaging tests such as computed tomography (CT) scan or magnetic resonance imaging (MRI). 

How Is Agnosia Treated?

There is no specific treatment for agnosia. The underlying cause will be treated if possible. Speech and occupational therapy can help you learn to compensate for your agnosia. They may also be able to help you improve your communication skills, plan tasks, solve problems, and improve your interactions with others.

Prognosis for Agnosia

The prognosis for agnosia depends on several factors such as:

  • Where the damage to your brain is located
  • How severe the damage is
  • How severe your symptoms are
  • How effective the treatment of the underlying cause is
  • Your age

You can start to improve during the first 3 months if whatever is causing the damage can be treated effectively. You may continue to improve for up to 1 year. 

Show Sources

SOURCES:

Alzheimer's Association: "Parkinson's Disease Dementia."

American Association of Neurological Surgeons: "Traumatic Brain Injury."

American Stroke Association: "Ischemic Stroke (Clots)."

Cleveland Clinic: "Alzheimer's Disease.",

GARD: "Agnosia."

Harvard Health Publishing: "Brain Abscess."

MAYO CLINIC: "Brain tumor."

MERCK MANUAL: "Agnosia."

National Institute of Neurological Disorders and Stroke: "Agnosia Information Page."

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