The Rationality of Psychosis and Understanding the Deluded
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Philosophy, Psychiatry, & Psychology 11.1 (2004) 35-41

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The Rationality of Psychosis and Understanding the Deluded

Matthew R. Broome

Campbell's important and influential paper (Campbell 2001) has framed the debate that Bayne and Pacherie (2004) most explicitly, and Klee (2004) and Georgaca (2004) more implicitly, engage in. Campbell has offered two broad ways of thinking about explanations of delusions—the empirical and the rational. He offers some criticism of the former and an endorsement of the latter. Campbell uses examples from clinical psychopathology to illustrate his argument and Bayne and Pacherie in turn employ these. Campbell discusses the eponymously named delusions of Capgras and Cotard—the former a subtype of delusional misidentification and the latter a delusion whose content is colored predominantly with nihilistic and possibly hypochondriacal themes. Campbell, Bayne and Pacherie, and Klee discuss the empirical data in relation to such delusions and as an aid to discussing the empirical model more generally. It does seem a little unfortunate that these delusions, which are less than typical, become the focus of Campbell's paper, and Bayne and Pacherie's criticism of his work. Delusions are remarkably heterogeneous; this indeed may be part of the reason why there is so much difficulty in reaching a definition as Klee discusses, and occur in a wide variety of mental and neurological illnesses. The most common delusions are those of persecution and reference (World Health Organization [WHO] 1973) and typically occur in schizophrenia. By contrast, delusional misidentification occurs most commonly in patients with dementia, delirium, and focal cognitive impairment, but can occur in other functional psychoses such as an affective or schizophrenic psychosis. The most common form of delusional misidentification is not that of either the exotic Capgras or Fregoli syndromes but delusional misidentification for place; thus, although Bayne and Pacherie's arguments against Campbell may still hold, delusional misidentification tends to occur in the context of a patient believing that they are at home or on holiday rather than in hospital and may not necessarily involve close family members or other intimate relationships. Similarly, Cotard's syndrome tends to occur in the context of a severe depressive illness with mood-congruent psychotic symptoms, typically in an elderly individual. It does not have to have the content that the deluded is dead, but can include beliefs, for example, that the world no longer exists or that their internal organs are not present. Thus, a patient with either Capgras' or Cotard's syndrome is likely to differ from patients with delusions of persecution. They would [End Page 35] have different diagnoses, probably be older, and have a greater likelihood of structural abnormalities of the brain on imaging and consequent neuropsychological dysfunction. That is not to say that patients with schizophrenia have normal cerebral anatomy and neuropsychology, but rather that the Capgras' and Cotard's patients are likely to have neurological quality to their presentation that is clinically relevant, rather than what commonly the case in schizophrenia and the other functional psychoses, where the neurological abnormalities are only currently important at the level of academic research.

Empirical Models of Delusion Formation

Different delusions may not have that much in common, nor may the patients who believe in them. This in turn relates to the empirical paradigm that both Campbell and Bayne and Pacherie discuss. It is true that current research, and indeed the clinical practice of cognitive behavioral therapy for psychosis, is indebted to the work of Maher and it is within his legacy which we work. This, however, is not to say that we think his initial formulation was correct. Maher's (1988, 1992) work focused attempts in explaining delusions—both to support and refute his thesis that delusions are the consequence of normal cognitive mechanisms seeking to explain an anomalous sensory experience. Such a view initially led to work demonstrating delusions in the absence of anomalous perceptions, the presence of reasoning biases in the deluded population, and the possibility that abnormal sensory experience may be consequent upon biased cognitive processes (Garety and Freeman 1999). More recent work has demonstrated the prevalence of...