ANOSOGNOSIA AND HALLUCINATIONS

   The term anosognosia comes from the Greek words a (not), nosos (illness), and gnosis (insight). It translates loosely as 'lack of knowledge of one's illness'. The French neologism anosog-nosie was introduced in or shortly before 1914 by the Polish-French neurologist Joseph Jules François Félix Babinski (1857-1932). The phenomenon itself was described at least as early as 1885 by the Russian-Swiss neuropathologist Constantin von Monakow (1853-1930). Today anosognosia is defined as a failure to recognize the existence of a defect, disability, or disorder involving one's own body. In a restricted sense, the term has a specific bearing on the non-recognition of neurological disabilities due to right hemispheric lesions, such as left-sided hemiparesis, homonymic "hemianopia, and unilateral " deafness.This type of anosognosia may be complicated by visuo-spatial neglect, i.e. a lack of awareness of a specific area or side of one's body. The neurophysiological correlates of this type of anosognosia are not fully known. There is, however, general consensus on the involvement of the right parietal lobe. It has been suggested that the involvement of other CNS structures may be required for the mediation of anosognosia as well, including the right optic thalamus or the right thalamoparietal radiation. The term anosognosia is also used in a wider sense to include phenomena such as denial of " blindness (as in the " Anton-Babinski syndrome), denial of illness in Huntington's disease or " psychotic disorder, and psychological denial of trauma. In all types of anosognosia, confabulations and hallucinatory experiences may be invoked to explain away the problem. In addition, it has been suggested that anosognosia in hemi-plegic individuals may be due to " proprioceptive or " kinaesthetic hallucinations experienced in the affected body region, which are interpreted either as 'proof' of actual function or as 'proof' of another person being present at the affected side. Two examples of the latter syndrome are known under the names " altruistic hallucination and " somatoparaphrenia.

   References

   Von Monakow, C. (1885/ Experimentelle und pathologisch-anatomische Untersuchungen über die Beziehungen der sogenannten Sehsphäre zu den infracorticalen Opticuscen-tren und zum N. opticus. Archiv für Psychiatrie und Nervenkrankheiten, 16, 151-199.

   Babinski, J. (1914). Contribution à l'étude des troubles mentaux dans l'hémiplégie organique cérébrale (anosognosie). Revue Neurologique, 27, 845-848.

   Kelly, C. (1992). Status and investigation of body image delusions.In: Delusions and hallucinations in old age. Edited by Katona, C., Levy, R. London: Gaskell.