What is Agnosia?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 08 November 2019
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Agnosia is a condition in which someone cannot correctly interpret sensory stimuli. This condition is most classically caused by brain damage, and it cannot be cured, although patients can work with therapists who can help them cope with the agnosia. This condition can occur in conjunction with other neurological disorders, and this condition can in fact be a sign that someone is experiencing a neurological problem.

In visual agnosia, the patient fails to recognize objects he or she sees. Patients who suffer from auditory agnosia cannot interpret sounds correctly, and patients with tactile agnosia have difficulty recognizing physical sensations. For example, someone might see an apple and be unable to say that it is red, or to recognize that it is an apple.

People who have experienced strokes, head trauma, brain cancer, and oxygen deprivation are all at risk of developing this neurological condition. Damage to the brain can cause the appearance of brain lesions, areas of injury in the brain. In some cases, the brain can compensate for a lesion by re-routing information to an undamaged area, but in other instances the brain may not be able to cope, and the patient will develop agnosia.


The term “agnosia” comes from the Greek for “not knowing,” and the condition can take a variety of forms. For example, people might experience alexia, in which they are unable to comprehend text, or problems with color recognition in which they cannot recognize and name colors. Some other variants can cause people to be unable to interpret speech, or to be unable to hear. The condition can vary considerably from patient to patient, reflecting the complexity of the human brain.

In true cases, the patient's sense is not damaged, there is simply a problem with the brain's interpretation of that sense. For example, if someone appears to be deaf after a brain injury, it would only be classified as agnosia if the sense of hearing is intact, but the brain cannot interpret the information. The condition reflects a genuine loss of knowledge, rather than a sensory or intellectual deficit.

For patients, agnosia can be extremely frustrating, because it can limit their ability to communicate with other people or to understand the world. For people who have been living highly functional lives, agnosia can cause depression as the patient struggles to adjust. Neurologists and therapists can work with patients to help them learn to work with their loss of knowledge, and to provide tools which can be used for expression and communication in the case of patients who struggle with these aspects of human interaction.


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