Understanding and treating persecutory delusions: an interventionist-causal model approach

Paranoia denotes the fear that others intend to cause you harm. Like other psychiatric problems such as fears and phobias, there is a spectrum of severity of paranoia. It occurs most dramatically as delusions of persecution, but is related to suspicious thoughts that occur in 10-20% of the general population. There is a pressing need to develop better treatment. One way to achieve this is to draw upon knowledge of the causes of the problem. If a potential factor is causal, then by deliberately increasing or decreasing it there will be an effect on paranoia. In a unique programme, four studies will be carried out that take such an approach to paranoia. Manipulationist studies provide techniques that can be incorporated into treatments; this has been particularly demonstrated for anxiety disorders and the aim is to emulate this for paranoia. The final study will bring together all the applicant‘s work in a test of a new treatment package for persecutory delusions. Particular use will be made of virtual reality social environments, which provide an excellent means of studying and potentially treating paranoia. Importantly, new information on the effects of cannabis, the most commonly used illicit substance, will also be gained.

Persecutory delusions are the most distressing delusion type, the most likely to be acted upon, and are a predictor of admission to psychiatric hospital. Existing treatments, pharmacological and psychological, are only partially effective. It is therefore urgent that we demonstrate the mechanisms underlying this important clinical experience in order to develop better treatments. Statisticians and philosophers of science, and now a number of psychologists and psychiatrists in relation to mental illness, are highlighting the need to adopt an ‘interventionist-causal‘ approach, illuminating causal inference by manipulating key factors. For instance, if paranoia builds upon negative cognitions about the self then altering such negative ideas will change paranoid thinking. The manipulations have the benefit of being readily incorporated into treatments. The objective of the new fellowship programme is to carry out a series of interventionist-causal studies of clinical and non-clinical paranoia, drawing upon the applicant‘s theoretical model, which can then be used to develop a better cognitive treatment. Because paranoid thought typically concerns others‘ behaviour, a key feature of the research will be the use throughout of virtual reality social environments. Four novel randomised controlled studies will be carried out testing causal roles in paranoia for anomalous experiences, cognitive interpretation, and affective processes. The role of the misinterpretation of anomalous experiences will first be tested by intravenous administration of delta-9-tetrahydrocannabinol (the active ingredient of cannabis). Included will be the first examination of the effects of cannabis on paranoia-related cognitive processing. The effect of visual perceptual anomalies will then be examined in a study that will enable virtual environments to be used as a learning tool. The theoretical model hypothesis that persecutory delusions are threat beliefs maintained by safety behaviours will be tested by repeated behavioural experiments in virtual reality, based on methods developed for anxiety disorders. A focused intervention for low self-esteem will be used to examine the effect on paranoia of decreasing negative ideas about the self. The culmination of the research will be a fifth study that provides an initial test of a new targeted modular treatment for persecutory delusions. The programme uniquely applies developments in theory, methodology, technology and treatment. A close interplay is made between theory, experiment, and treatment development. It will lead to: a much stronger theoretical understanding of persecutory delusions; new knowledge about the effects of cannabis; the first use of virtual reality to treat psychosis; and, importantly, a targeted treatment for persistent paranoia.