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The past and future of delusions research: from the inexplicable to the treatable

  • P. A. Garety (a1) and D. Freeman (a2)

Problems with the diagnosis and treatment of schizophrenia have led for a call to change strategy and focus on individual psychotic experiences. In recent years, research on delusions has led the way.


To update our 1999 review of almost 40 studies on delusions.


A systematic literature search was conducted of reasoning and affective processes related to delusions.


Over 200 studies were identified. The presence of jumping to conclusions' in individuals with delusions has been substantiated, the theory of mind account has not stood up to subsequent testing, and there is a promising new focus on the ways that affective processes contribute to delusional experience.


Theoretical work rendering delusions understandable can be translated into treatment; future clinical trials should focus on individual psychotic experiences as outcomes.

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Corresponding author
Professor P. A. Garety, Box PO77, Institute of Psychiatry, King's College London, De Crespigny Park, London SE5 8AF, UK. Email:
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The past and future of delusions research: from the inexplicable to the treatable

  • P. A. Garety (a1) and D. Freeman (a2)
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A transdiagnostic approach to delusion

Michele Poletti, Psychotherapist
15 December 2013

Garety and Freeman present an exhaustive updated review on delusions as a single symptom,1 suggesting some general conclusions: 1) the presenceof biased "jumping to conclusions" data-gathering reasoning processes represents a relative stable cognitive trait increasing susceptibility to delusion development; 2) emotion processes may influence the subjective experience associated with delusional states; 3) alterations of Theory of Mind do not mainly contribute to delusion development; 4) studies have been almost exclusively conducted on non-affective psychosis. Some of these issues were discussed in a recent paper2 in which we adopteda transdiagnostic approach to identify a core of neural and neuropsychological alterations at the basis of delusion development acrossdistinct clinical populations. With this aim we reviewed empirical studiesthat investigated neural and neuropsychological alterations in psychiatric(schizophrenia, bipolar disorder, depression) and neurological (neurodegenerative disorders) populations presenting delusions, and focusing on studies that directly investigated correlates of delusions, when available. Identified core neuroanatomical alteration involves ventromedial Prefrontal Cortex, basal ganglia, amygdala, insula and the Default Mode Network, whereas the core neuropsychological alteration involves reward processing, emotion processing, default mode, memory, social cognition and Self-related processes. The alteration of these processes could contribute to delusions by affecting the generation of affective value, the construction of internal models of the world or the reflection about the Self and other's mental states: delusions may be the result of abnormal Self-centered or Others'-centered internal models of subjective experiences of aberrant affective meaning. Coltheart's two factors-account for monothematic delusions3 suggests that a model of delusions should explain what brought the delusional idea to mind in the first place and why this idea is accepted as true and becomes a belief even if it is clearly bizarre and when plenty of evidence against it is available to the subject. In our model the trigger of delusional ideas is represented by unusual or bizarre experiences of aberrant affective value that the subject tries to explain, and the delusional idea is adopted as belief following altered processes of constructing internal models of the world and mentalizing about Self-Others.The proposed model had the strength to be based on a transdiagnostic analysis of possible neural and cognitive correlates of delusions, and therefore was not based only on delusion in non-affective psychosis, that is one of the limits of empirical research on delusion raised by Garety and Freeman: therefore I agree with them suggesting that more clues on theprocess of delusion development may come from the analysis of delusion as a single symptom comparing different clinical populations. Moreover, in the proposed model an altered process of reflection about the Self and other's mental states is needed for the development of delusion, while Garety and Freeman concluded that Theory of Mind deficits were not specific to delusions; however, some studies directly reported this association4,5 and therefore, on the basis of available data,1 it's not possible to discharge the hypothesis that, even if not specific to delusions, Theory of Mind alterations may play a role in their development.

References1.Garety PA, Freeman D. The past and the future of delusions research: from the inexplicable to the treatable. The British Journal of Psychiatry 2013; 203: 327-333.

2.Poletti M, Sambataro F. The development of delusion revisited: a transdiagnostic framework. Psychiatry Research 2013; 210: 1245-1259.

3. Coltheart M, Langdon R, McKay R. Delusional belief. Annual Review of Psychology 2011; 62:271-298.

4. Bentall RP, Rowse G, Shryane N, et al. The cognitive and affectivestructure of paranoid delusions: a transdiagnostic investigation of patients with schizophrenia spectrum disorders and depression. Archives ofGeneral Psychiatry 2009; 66: 236-247.

5. Montag C, Dziobek I, Richter IS, et al. Different aspects of theory of mind in paranoid schizophrenia: evidence from a video-based assessment. Psychiatry Research 2011; 186: 203-209.

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Conflict of interest: None declared

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Psychosis as a failure of reality testing

Andrew Shepherd, Doctor
02 December 2013

Garety and Freeman present a timely review on the nature of delusional experience.1 Their conclusion regarding the need to focus on individual features of psychosis seems apt. The presented overview of cognitive and affective mechanisms influencing delusion development seems,however, to overlook an essential component of delusional experience; thatpsychotic symptoms, including delusions, at their heart represent a failure of reality testing.

The description of jumping to conclusions, together with the probabilistic reasoning task methodology, appears to rely on a logical chain of thought progression and conclusion. What Campbell has referred toas an empiricist understanding.2 This approach however does not take into account the nature of conclusions reached in delusional belief: - Conclusions reached on seeing two, or less, coloured counters seem quite distinct from classical examples of delusional perception; "I saw the traffic lights turn green and realised that the world would end". Campbell's alternative rationalist approach presents the delusional subject as having experienced a complete rearrangement of their framework propositions, or underlying background world beliefs. Such a fundamental shift in world view model can go some way to explaining the fantastical nature of conclusions reached, or the failure of reality testing present in psychosis.

Campbell's arguments have not gone unchallenged.3 However what they do highlight is a need for careful consideration as to the manner in whichdelusional beliefs are formed. Garety and Freeman describe the psychoanalytic thinking in relation to defence mechanisms in the development of persecutory delusional belief. Psychotic defence concepts, wherein the subject denies or distorts reality to defend against trauma, provide one possible lens through which psychotic experiences can be viewed.4,5

Garety and Freeman's conclusion relating to the infancy of research into the nature of delusion, and its having been overshadowed by focus on the larger concept of Schizophrenia, highlights the need for further research. Future research will need to provide some account for the distortion of reality that seems central to the experience of psychosis.

1 Garety PA, Freeman D. The past and future of delusions research: from the inexplicable to the treatable. The British Journal of Psychiatry 2013.

2 Campbell J. Rationality, Meaning, and the Analysis of Delusion. Philosophy, Psychiatry, Psychology 2001; 8: 89-100.

3 Bayne T, Pacherie E. Bottom-Up or Top-Down: Campbell's Rationalist Account of Monothematic Delusions. Philosophy, Psychiatry, Psychology 2004; 11: 1-11.

4 Hingley SM. Psychodynamic perspectives on psychosis and psychotherapy. I: Theory. Br J Med Psychol 1997; 70(4): 301-12.

5 Martindale B, Summers A. The psychodynamics of psychosis. Advances in Psychiatric Treatment 2013; 19: 124-31.

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Conflict of interest: None declared

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