Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 24, 2016

Agnosia describes the inability of the brain to properly interpret sensory information. Those suffering from agnosia may be unable to recognize or identify certain objects correctly. Agnosia is caused by head injury or neurological disorder.


Definition & Facts

Agnosia comes in many different forms and can affect everything from the ability to speak to the ability to see motion. Of all of these types, visual agnosia and auditory agnosia are the most common.

In cases of auditory agnosia, the patient may be unable to understand the meaning of words despite experiencing no memory loss, hearing loss, or loss of intellectual capacity.

For those suffering from a visual form of agnosia, they may instead be unable to remember the face of a loved one, despite remembering the person in all other details.

Symptoms & Complaints

The symptoms of agnosia vary from person to person, but there are general tendencies that can help identify agnosia. In general, those dealing with agnosia will be unable to recognize some familiar sights or sounds.

If a person seems entirely aware of their surroundings and focused, but cannot remember what the word "door" means, it may well be a symptom of agnosia. Many people first discover their agnosia after leaving the hospital for a head injury or stroke, only to find that they cannot recognize buildings or people that were once familiar to them.

For those that suffer from agnosia, the most frustrating symptom is the feeling of knowing that they are missing something, but not being able to tell what it is. For these people, the feeling is similar to having a word on the tip of their tongue, but that word is instead something major like their mother's name.


Agnosia is always caused by damage to the brain, but the specific type of agnosia may differ based upon the location of the damage or the way it was inflicted. In the case of visual agnosia, the condition develops because the brain is unable to retrieve images from the parts of the brain that have been damaged, specifically the visual memory center.

In other forms, lesions from head trauma can grow over important areas of the brain, and a stroke or brain tumor can cause irreversible brain damage that results in agnosia. Agnosia has also been noted to occur in conjunction with other disorders of the brain, particularly in cases of Alzheimer's disease, dementia, and other diseases that involve gradual neurodegeneration.

While most cases of agnosia have definitive causes, there are a minority of cases where the cause of the brain damage remains unknown or idiopathic.

Diagnosis & Tests

Diagnosis for agnosia takes place both through brain scans and through object identification tests. A common test is to ask patients to identify common objects like furniture and foods using one of their five senses. If a person proves unable to identify what a fan is called by looking at picture, then they are likely suffering from a visual form of agnosia.

Another common test is to place a loved one in front of the patient and ask them to describe the person in terms of eye color, hair color, etc. If the person cannot see any of these items, or is unable to identify the loved one, then agnosia may be indicated.

Physical tests will be conducted to determine how much of the brain has been damaged and in what areas. This typically takes the form of medical imaging scans of the brain like computed tomography (CT) scans and magnetic resonance imaging (MRI)s, which allow doctors to receive a close and detailed look at the damage. Once the damage has been assessed, treatment can begin.

Treatment & Therapy

In cases of head trauma or cerebral hemorrhages, surgery may be performed to repair the damage and restore the damaged parts of the brain to working order. Treatment is not typically focused on treating the damage, however, as this is usually impossible, but on giving the patient as much independence as possible.

More commonly, the patient will undergo some form of physical therapy or speech therapy to help minimize the effects of agnosia on their life. This can allow patients with agnosia to learn to cope with their symptoms, even if those symptoms never lessen. For example, a person with a visual form of agnosia may learn to organize their shirts by color to lessen their confusion when their brain is processing these colors.

In most cases, patients will learn to rely on their other senses rather than the damaged one and are able to go on living their normal lives. In particularly rare cases where the patient has suffered substantial loss of one of their senses, they may simply have to learn to live without any use of that sense.

Prevention & Prophylaxis

Because agnosia is typically caused by a head injury, there is not much that can be done to prevent its development.

For those suffering from neurological conditions like Alzheimer's or dementia, however, it is important to regularly attend doctor's visits and receive regular brain scans to ensure that agnosia can be identified as quickly as possible.

This will allow the patient to understand their situation much earlier on as well as give them an easier time adapting to the effects of agnosia.

For similar reasons, it is advised that anyone that suffered recent head trauma carefully examine their senses. If it seems that they are unable to remember things as clearly as before, or have lost the use of one of their senses, then they should speak with a doctor about the possibility of having developed agnosia.

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