Anosognosia

Anosognosia is a deficit of self-awareness, a condition in which a person with a disability is unaware of its existence. It was first named by the neurologist Joseph Babinski in 1914. Anosognosia results from physiological damage to brain structures, typically to the parietal lobe or a diffuse lesion on the fronto-temporal-parietal area in the right hemisphere, and is thus a neurological disorder. While this distinguishes the condition from denial, which is a psychological defense mechanism, attempts have been made at a unified explanation. Anosognosia is sometimes accompanied by asomatognosia, a form of neglect in which patients deny ownership of body parts such as their limbs. The term is from Ancient Greek ἀ- a-, 'without', νόσος nosos, 'disease' and γνῶσις gnōsis, 'knowledge'. Anosognosia is a deficit of self-awareness, a condition in which a person with a disability is unaware of its existence. It was first named by the neurologist Joseph Babinski in 1914. Anosognosia results from physiological damage to brain structures, typically to the parietal lobe or a diffuse lesion on the fronto-temporal-parietal area in the right hemisphere, and is thus a neurological disorder. While this distinguishes the condition from denial, which is a psychological defense mechanism, attempts have been made at a unified explanation. Anosognosia is sometimes accompanied by asomatognosia, a form of neglect in which patients deny ownership of body parts such as their limbs. The term is from Ancient Greek ἀ- a-, 'without', νόσος nosos, 'disease' and γνῶσις gnōsis, 'knowledge'. Relatively little has been discovered about the cause of the condition since its initial identification. Recent studies from the empirical data are prone to consider anosognosia a multi-componential syndrome or multi-faceted phenomenon. That is it can be manifested by failure to be aware of a number of specific deficits, including motor (hemiplegia), sensory (hemianaesthesia, hemianopia), spatial (unilateral neglect), memory (dementia), and language (receptive aphasia) due to impairment of anatomo-functionally discrete monitoring systems. Anosognosia is relatively common following different causes of brain injury, such as stroke and traumatic brain injury; for example, anosognosia for hemiparesis, (weakness of one side of the body) with onset of acute stroke is estimated at between 10% and 18%. However, it can appear to occur in conjunction with virtually any neurological impairment. It is more frequent in the acute than in the chronic phase and more prominent for assessment in the cases with right hemispheric lesions than with the left. Anosognosia is not related to global mental confusion, cognitive flexibility, other major intellectual disturbances, or mere sensory/perceptual deficits. The condition does not seem to be directly related to sensory loss but is thought to be caused by damage to higher level neurocognitive processes that are involved in integrating sensory information with processes that 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 people seem unable to attend to, or sometimes comprehend, anything on a certain side of their body (usually the left). Anosognosia can be selective in that an affected person with multiple impairments may seem unaware of only one handicap, while appearing to be fully aware of any others. This is consistent with the idea that the source of the problem relates to spatial representation of the body. For example, anosognosia for hemiplegia, or the paralysis of one side of the body, may occur with or without intact awareness of visuo-spatial unilateral neglect. This phenomenon of double dissociation can be an indicator of domain-specific disorders of awareness modules, meaning that in anosognosia, brain damage can selectively impact the self-monitoring process of one specific physical or cognitive function rather than a spatial location of the body. There are also studies showing that the maneuver of vestibular stimulation could temporarily improve both the syndrome of spatial unilateral neglect and of anosognosia for left hemiplegia. Combining the findings of hemispheric asymmetry to the right, association with spatial unilateral neglect, and the temporal improvement on both syndromes, it is suggested there can be a spatial component underlying the mechanism of anosognosia for motor weakness and that neural processes could be modulated similarly. There were some cases of anosognosia for right hemiplegia after left hemisphere damage, but the frequency of this type of anosognosia has not been estimated. Those diagnosed with Alzheimer's disease often display this lack of awareness and insist that nothing is wrong with them. Anosognosia may occur as part of receptive aphasia, a language disorder that causes poor comprehension of speech and the production of fluent but incomprehensible sentences. A patient with receptive aphasia cannot correct his own phonetics errors and shows 'anger and disappointment with the person with whom s/he is speaking because that person fails to understand her/him'. This may be a result of brain damage to the posterior portion of the superior temporal gyrus, believed to contain representations of word sounds. With those representations significantly distorted, patients with receptive aphasia are unable to monitor their mistakes. Other patients with receptive aphasia are fully aware of their condition and speech inhibitions, but cannot monitor their condition, which is not the same as anosognosia and therefore cannot explain the occurrence of neologistic jargon. Although largely used to describe unawareness of impairment after brain injury or stroke, the term 'anosognosia' is occasionally used to describe the lack of insight shown by some people with anorexia nervosa. They do not seem to recognize that they have a mental illness. There is evidence that 'anosognosia' related to schizophrenia may be the result of frontal lobe damage. E. Fuller Torrey, a psychiatrist and schizophrenia researcher, has stated that among those with schizophrenia and bipolar disorder, anosognosia is the most prevalent reason for not taking medications.