“Theory of mind”, persecutory delusions and the somatic marker mechanism

Abstract

Introduction. Pure cases of persecutory delusions can be interpreted as “theory of mind delusions”; using a model that equates the theory of mind mechanism with the “somatic marker mechanism” as described by Damasio and colleagues. Three predictions were tested in a case study design: that pure cases of persecutory delusions could be found, that such cases would retain normal theory of mind reasoning abilities, and that delusions would be encapsulated to a specific group of persecutors with hostile intentions. Method. The caseload of 17 psychiatrists and 4 community psychiatric nurses was surveyed for “pure cases” of persecutory delusions. Cases were excluded when there was evidence of other psychopathology, intellectual impairment, abnormal reasoning, “psychotic” features, or diagnostic syndromes. Selected cases were evaluated for the scope of their delusional beliefs and the nature of their social relationships using a detailed semistructured interview that was transcribed verbatim, and putative “theory of mind tests” as devised by Corcoran and Frith. Results. Thirty-four potential cases were referred among which four pure cases of encapsulated persecutory delusions were eligible for the study. All were men, aged between 32 and 43. Apart from their persecutory delusions, cases were free from other detectable pathology in their reasoning processes, affect, or social interactions - and scored highly on the putative “theory of mind tests”. Identified persecutors were males, and delusions involved false beliefs concerning the threat of violence from gangs of strangers. Conclusions. Pure cases of severe but encapsulated persecutory delusions can be found, and such cases demonstrate intact theory of mind reasoning ability. The nature of persecutory delusions is understandable in terms of the somatic marker mechanism, and the content of delusions is consistent with the nature of hostile threats to men in the ancestral human environment.