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Anosognosia is a condition in which a person who suffers disability due to brain injury or mental disorder, seems unaware of or denies the existence of their handicap. This may include unawareness of quite dramatic impairments, such as blindness or paralysis. It was first named by neurologist Joseph Babinski in 1914, although relatively little has been discovered about the cause of the condition since its initial identification. The word comes from the Greek words "nosos" disease and "gnosis" knowledge.
Anosognosia is relatively common following brain injury (e.g. 20-30% in the case of hemiplegia/hemiparesis after stroke), but can appear to occur in conjunction with virtually any neurological impairment. However, it is not related to global mental confusion (see delirium), cognitive flexibility, or other major intellectual disturbance. Anosognosia can be selective in that an affected person with multiple impairments may only seem unaware of one handicap, while appearing to be fully aware of any others.
The condition does not seem to be directly related to sensory loss and is thought to be caused by damage to higher level neurocognitive processes which are involved in integrating sensory information with processes which support spatial or bodily representations (including the somatosensory system). Anosognosia is thought to be related to unilateral neglect, a condition often found after damage to the non-dominant (usually the right) hemisphere of the cerebral cortex in which sufferers seem unable to attend to, or sometimes comprehend, anything on a certain side of their body (usually the left).
Although largely used to describe unawareness of impairment after brain injury, the term 'anosognosia' is now also used to describe the lack of insight shown by some people who suffer from psychosis, and who may be unaware that their outlandish beliefs and experiences are in any way unusual. Those in a manic phase of bipolar disorder may also exhibit anosognosia. However, this usage of the term is controversial even among psychiatrists. 
There are currently no long-term treatments for anosognosia, although, like unilateral neglect, Caloric reflex testing (squirting ice cold water into the left ear) is known to temporarily ameliorate unawareness of impairment. It is not entirely clear how this works, although it is thought that the unconscious shift of attention or focus caused by the intense stimulation of the vestibular system temporarily influences awareness. Most cases of anosognosia appear to simply disappear over time, while other cases can last indefinitely. Normally, long-term cases are treated with cognitive therapy to train the patient to adjust for their inoperable limb/s (though it is believed that these patients still are not "aware" of their disability).
Due to its disabling effects, anosognosia is now being increasingly studied. Researchers of this condition include neurologists Vilayanur S. Ramachandran and Oliver Sacks, and neuropsychologist George Prigatano.
- Brain damage
- Coping behaviour
- Dunning-Kruger Syndrome
- Glossary of psychiatry
- Illness behavior
- Vilayanur S. Ramachandran
- Oliver Sacks
- Unilateral neglect
- Amador, X.F., David, A.S. (2004) Insight and Psychosis: Awareness of Illness in Schizophrenia and Related Disorders (2nd ed). Oxford: Oxford University Press. ISBN 0198525680
- Prigatano, G. and Schacter, D. (eds) (1991) Awareness of Deficit After Brain Injury: Clinical and Theoretical Issues. Oxford: Oxford University Press. ISBN 0195059417
- Anosognosia: The neurology of beliefs and uncertainties. Vuilleumier, P. (2004) Cortex, 40, 9-17.
- Vilayanur S. Ramachandran (1998) Phantoms in the Brain New York: Quill (HarperCollins Publishing). ISBN 0688172172
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