Anosognosia: Possible Neuropsychological Mechanisms

Anosognosia is the denial of illness that may be seen in brain-injured patients. In general, denial of illness takes two forms. There may be verbal, explicit denial of illness, or there may be a lack of genuine concern about the deficit. The verbal explicit denial is termed anosognosia, and indifference has been termed anoso-diaphoria (Critchley, 1953). Anosognosia was first described by Von Monakow (1885) and Anton (1896). However, it was Babinski (1914) who first coined this term. Whereas subsequently anosognosia has been noted by many other authors, these important signs have not been the prime target of intensive investigation as has been the case with aphasia, alexia, and amnesia. Despite the lack of interest, these behavioral aberrations are not trivial. Not only may anosognosia impair a patient's desire to seek medical aid, it may also impair his desire to seek rehabilitation or to benefit from rehabilitation programs. Perhaps equally important, neuropsychological studies of anosognosia may help us understand not only why patients deny their illness but also myriad other behavioral anomalies such as hypochondriasis, where a physically healthy person is convinced that he is ill. Hypochondriasis may be the mirror of anosognosia. This article is not an extensive review of anosognosia, rather it is a discussion focusing on the neuropsychological mechanism that may be responsible for the various forms of anosognosia. The reader must be forewarned, however, that there are many unanswered questions and that much of what is discussed is speculative. The basic posulate that I will pursue is that anosognosia is a failure of monitoring and may be related to (1) an impaired monitor, (2) the absence of feedback, (3) false feedback, and (4) the improper setting of the monitor. Anosognosia is seen with many behavioral syndromes. I discuss the following three: Wernicke's aphasia, Anton's syndrome, and left hemiplegia (denial of