Agnosia

Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells. The specific sense is not defective nor is there any significant memory loss. It is usually associated with a brain injury or neurological illness.

There are 3 forms of Agnosia:

  • Visual Agnosia. A person cannot recognize people or objects even though there is no abnormality of the eyes or the visual system.

  • Auditory Agnosia. A person cannot hear things such as words, environmental sounds or music, but can hear other sounds.

  • Somatosensory Agnosia. A person cannot tell what an object is by touching it.

People with agnosia do not suffer from general memory loss. Patients may have visual agnosia with or without the other forms of agnosia.

There are several forms of visual agnosia:

  • Prosopagnosia. An inability to recognize a person's face. This happens even if the person with visual agnosia knows the other person.

  • Agnostic Alexia. An inability to recognize written letters or words.

  • Color Agnosia or Cerebral Achromatopsia. An inability to tell the difference between colors or name colors. This differs from color blindness, which is a genetically determined disorder.

  • Object Agnosia. An inability to recognize and name an object.

  • Simultanagnosia. An inability to recognize an entire object, even though the individual may be able to recognize and name parts of the object.

CAUSES

  • Diseases or disorders of specific regions of the brain. It is usually the left parts of the brain.

  • Bleeding (hemorrhage) or lack of blood supply to those regions of the brain (stroke or cerebral vascular accident).

  • Brain tumors.

  • Cancer that spreads to the brain from another part of the body (metastatic cancer).

  • Trauma.

  • Abnormalities (lesions) that occur on both sides of the brain in the occipital and temporal lobes(prosopagnosia).

  • Diseases of the outside lining of the nerves that make up the brain and body's peripheral nerves (demyelinating diseases).

  • Multiple sclerosis.

  • Certain rare brain diseases (Nielsen-Jacobs Syndrome).

  • Carbon dioxide poisoning.

  • Lack of oxygen.

  • Memory loss (dementia).

  • Passed down from a parent (heredity).

  • Brain infection (meningitis, encephalitis).

SYMPTOMS

There are 2 stages of visual agnosia:

  • Apperceptive Agnosia.This is a more severe type of visual agnosia. The affected person has an inability to group or manipulate an object that can only be seen. They may not be able to distinguish shape or even say if they have seen a similar object before. They may have a hard time copying simple drawings.

  • Associative Agnosia.This is a less severe form of visual agnosia. The person has a vague sense of the object that they cannot recognize. People in this stage of agnosia can copy drawings but are unaware of what the drawing is. They also have a hard time giving words to what they see.

DIAGNOSIS

  • Neurological exams and testing.

  • More tests may be requires to find the cause.

TREATMENT

  • Certain exercises are done. These exercises help the person identify objects. Usually treatment starts with objects that are needed for independence. In order to identify necessary objects, the patient learns to keep objects in a specific place, or to make lists of where things should be so. That way, when they do see something, they already expect it to be what they are searching for.

  • They learn to use labels for objects of necessity.

  • By using both approaches, it may help the patient recognize objects and maximize independence.