Agnosia is an acquired recognition disorder. In terms of interpretation of sensory information, this disorder can affect different senses, such as vision (visual agnosia), hearing (auditory agnosia), and touch (tactile agnosia).
What is agnosia?
Agnosia is a recognition disorder where a person suffering from it cannot recognize familiar objects, sounds, smells, or faces.
Agnosia differs from other sensory disorders that are caused by a primary sensory deficit. In other words, a person with agnosia has a normal sensory function (hearing, vision, and touch). The development of agnosia disorders is related to the transmission and/or interpretation of sensory information. At the level of the brain, alteration of sensory memory may explain the occurrence of certain recognition disorders.
Agnosia usually affects only one sense. The most common forms are visual, auditory, and tactile agnosias.
- Visual agnosia occurs when a person is unable to recognize certain familiar objects, shapes, or signs with the naked eye. However, visual agnosia should not be confused with visual impairment, which is characterized by decreased visual acuity.
- Depending on the case, visual agnosia may be associated with a problem interpreting information about space, shapes, faces, or colors. As such, it is possible to distinguish:
- Object agnosia, which may be associated with associative agnosia with the inability to name an object present in the visual field, or with apperceptive agnosia with the inability to name and draw an object present in the visual field.
- Prosopagnosia, which affects the recognition of familiar faces, both those of close people and the patient’s own.
- Color agnosia, which is characterized by an inability to name different colors.
Auditory agnosia is the inability to recognize certain familiar sounds. Depending on the case, it is possible to distinguish:
- Cortical deafness, which is characterized by the inability to recognize familiar sounds, familiar noises, or music.
- Auditory verbal agnosia (AVA), characterized by the inability to understand spoken language.
- Amusia, which refers to the inability to recognize melodies, rhythms, and tones of voices.
Tactile agnosia is characterized by the inability to recognize an object by simple palpation. This recognition disorder may be related to the material, weight, volume, and shape of the object.
Asomatognosia is a special form of agnosia. It is characterized by the loss of recognizability of a part or of the whole body. Depending on the case, it is possible to distinguish:
- Autotopoagnosia, which is characterized by the inability to recognize different parts of one’s own body.
- Finger agnosia, which affects only the fingers.
What are the causes of agnosia?
Agnosia disorders can have different explanations. They are often due to the development of brain damage as a result of :
- A stroke, sometimes called cerebral infarction, caused by a circulatory disorder of the brain.
- A head injury, a blow to the skull that can cause brain damage.
- Neurological disease, including dementia and neurodegenerative diseases such as Alzheimer’s disease.
- A brain tumor, which results from the development and proliferation of abnormal cells in the brain.
- A brain abscess.
What are the consequences of agnosia?
The consequences and course of agnosia depend on many parameters, including the type of agnosia, the cause of the symptoms, and the patient’s condition. Agnosia disorders cause discomfort in everyday life, which may be more or less hard to deal with depending on the case.
How to treat agnosia disorders?
The treatment consists of treating the cause of agnosia. It depends on the diagnosis, which is usually made by clinical examination and is supplemented by thorough medical examinations. In particular, neuropsychological testing and brain imaging studies may be performed to confirm the diagnosis.
Treatment of agnosia is often accompanied by rehabilitation to improve the quality of life of those affected. This rehabilitation may involve several specialists, including occupational therapists, speech therapists, and physical therapists.