Agnosia

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Agnosia

Imagine looking through a window and seeing a complete stranger staring back at you. Oddly, they are wearing your clothes. How strange or curious would this situation be for you? You might be able to empathize with a person who has a visual agnosia; each time they look into a mirror and see their own reflection, they perceive a completely unfamiliar person looking back at them. Agnosia (literally: a-, without; gnōsis, knowledge) is a type of psychological disorder, recognized by the DSM-IV as a form of dementia, characterized as a disturbance of cognitive functioning (DSM-IV, 1994). Agnosia can be expressed by the inability to recognize familiar objects or even people. It is directly related to brain injuries or diseases that damage a certain area of the brain. Since agnosia is related to brain damage, one injury may cause a different symptom than another, depending on where the damage is located. There are many different types of agnosia diagnoses that aim to describe the variety of symptoms people may display. There have been several intriguing case studies on agnosia, however, there is still relatively little known about how to treat this affliction. Agnosia is typically caused by age related degradation or trauma to a specific brain region. Most agnosia is associated with damage to areas the parietal, temporal, or occipital lobes of the brain. These among these lobes are regions for encoding and decoding sensory perceptions as well as memory storage and retrieval. Severe head injury is the most common cause of agnosia but is not the only cause for developing agnosia. In some cases Agnosia has been reported in patients who have had a stroke or brain infections such as encephalitis. In these cases the parietal lobe is very susceptible to damage. Agnosia is caused by head trauma and aging, therefore anyone can develop this disorder. There are various subtypes of agnosia because of the broad range in symptoms, which are usually linked to senses such as sight and sound. A few common types of agnosia subtypes are prosopagnosia, auditory agnosia, mirror agnosia, and associative agnosia. Each agnosia is manifested by a unique set of symptoms. Prosopagnosia is also known as “face blindness” because patients have the inability to identify or see faces. Generally in prosopagnosia faces become almost featureless and are described as “stone faces.” Auditory agnosia is the inability to hear environmental sounds such as a dog barking or a car door slamming. One of the symptoms of mirror agnosia is hemispatial neglect; when a patient has hemispatial neglect, one half of their visual field does not register. If an object is placed in the neglected field and a mirror is situated in the normal field, a patient will attempt to reach for the object in the mirror because they are unable to see the object in the unused visual field. In associative agnosia, patients will not be able to recognize simple objects such as a key or a phone. If a patient is asked to copy a picture of these once familiar objects they will be able to copy detail but once you ask them what the object is they can not decipher what they are drawing. Treatments for agnosia patients are typically aimed to improve the lives of these individuals by reducing the severity of the symptoms by behavioral therapy or clever prosthetic devices and schemes, but as a whole there is no direct biological cure. Agnosia patients can receive speech or occupational therapy to help them cope with their symptoms. Some visual agnosia patients have developed some adaptive strategies to help them overcome their disability, such as labeling objects or keeping them in a specific place. These strategies can help them with their short term goals in identifying a needed utensil, tool, comb, or other object, however, these techniques are merely a crutch that helps them cope with the day to day grind. In time, scientists aim to formulate therapies that will provide these patients with a more sustainable treatment – by recovering normal brain function.



Bibliography

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: First, M.B., Frances, A., Pincus, A.H.