Friday 7 June 2013

Delusions in the DSM 5

This post is by Lisa Bortolotti.

How has the definition of delusions changed in the DSM 5? Here are some first impressions.

In the DSM-IV (Glossary) delusions were defined as follows:

Delusion. A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person's culture or subculture (e.g., it is not an article of religious faith). When a false belief involves a value judgment, it is regarded as a delusion only when the judgment is so extreme as to defy credibility.

This is how delusions are described in the DSM-5 (Schizophrenia Spectrum and Other Psychotic Disorders):

Delusions are fixed beliefs that are not amenable to change in light of conflicting evidence. Their content may include a variety of themes (e.g. persecutory, referential, somatic, religious, grandiose).[…] Delusions are deemed bizarre if they are clearly implausible and not understandable to same-culture peers and do not derive from ordinary life experiences. […] The distinction between a delusion and a strongly held idea is sometimes difficult to make and depends in part on the degree of conviction with which the belief is held despite clear or reasonable contradictory evidence regarding its veracity.

Although differences are not very significant, I do welcome some of the noticeable shifts.

First, as many philosophers and psychologists have noticed when commenting on the DSM-IV definition (e.g., Davies et al. 2001, pp. 133-134; Coltheart 2007, p. 1043), delusions need not be false, and being false is no longer a necessary condition for a belief to be delusional in the DSM-5 description.

Second, delusions do not need to be about external reality or to be based on incorrect inference. They could be about oneself and one’s own experiences, requiring little or no inference.

Third, we may have no proof against the truth of a belief, even when the belief is wildly implausible, and this is reflected in the move from the phrase “despite what constitutes incontrovertible and obvious proof or evidence to the contrary” to the phrase “despite clear or reasonable contradictory evidence regarding its veracity”.

More important, in my eyes the new account narrows the gap between delusions and other irrational beliefs, suggesting that the epistemic features of delusions are not unique to pathologies of the mind, but characterise many of our everyday beliefs.

One change I would have welcomed is the recognition that, although delusions are very resistant to counter-evidence and counter-argument, they are not totally impervious to cognitive probing. There are some interesting case studies suggesting that people can give up their delusion after being invited to reason about the inconsistencies that the delusion is introducing in their belief systems (e.g., McKay & Cipolotti 2007).

Something to consider for DSM-6...


  1. Hello! We have a strict 500 word limit for posts on Imperfect Cognitions, so I left out some bits of the texts where examples of delusions were offered or I wouldn't have had any space for comments! The page reference is 87.

  2. It is interesting that religious belief (or lack of it) is explicitly ruled out. Are the brain mechanisms behind delusions actually different from those behind belief in a supernatural agent or refusal to believe in one? If so, and it depends on whether the belief is held by same-culture peers, how many such peers do there have to be before the "delusion" ceases to be one? Again, what objective differences in brain mechanisms arise as the number of peers changes from the "delusional" state to the "cultural" state?

    1. i know this is a bit johnny come lately, but could you explain what you mean by 'explicitly ruled out'? i'm not sure i see it.

    2. The DSM IV definition is the reason why Richard Dawkins called his bestseller "The God Delusion".

      He found it revealing that it was not possible to define a delusion with objective criteria without covering religion as well. Because the author of the DSM IV definition clearly did not want religious faith into his definition of delusion, he then had no other choice but to create an explicit exception.

    3. I think what they're getting at in the religious exception is that religious belief is based on what you've been told by people you trust, while delusional beliefs come out of nowhere. So, you can believe something because you've seen evidence that it's true, you can believe something because you've been told it's true, or you can believe something for no apparent reason whatsoever. Only the last type of belief qualifies as a delusion.

  3. Hi Eric and thank you for your comments.

    My understanding of the DSM definition is that it makes no reference to the brain mechanisms underlying the formation of delusions and describes instead how people with delusions behave. In particular, it focuses on the epistemic features of such behaviour (beliefs being fixed, resistant to counter-evidence, etc.).

    This generates problems when we want to distinguish delusions from other beliefs which share some of the epistemic features of delusions, such as some religious beliefs or beliefs that are implausible but held by groups of people (e.g. beliefs in alien abduction).

    Psychologists looking into delusion formation are making very interesting hypotheses about what can distinguish delusions from other beliefs with similar characteristics - and they do refer to brain mechanisms broadly conceived (e.g. two-factor theories of delusions and prediction-error theories). I'm not sure whether they succeed in providing a demarcation but they are trying - I guess time will tell us.

    One question is whether the DSM should include information about brain mechanisms underlying psychiatric disorders and symptoms when some consensus in the scientific community is reached. Part of the lively debate about validation which preceded the publication of DSM 5 addressed precisely this question.

  4. You are absolutely right. As Kengo noticed in today's post, I should have specified in the post that one definition was taken from the Glossary (the DSM IV one) and one from the description of schizophrenia (the DSM 5 one) - I might update the post to reflect this to avoid confusion.

    As you point out, in the Glossary the definition is almost unchanged, but in the description I think there are at least two important shifts (the one from false beliefs to fixed beliefs, and the one from characterising delusions as the product of inference to leaving it unspecified how they may be formed).

    The result is that in DSM 5 there is some tension between the Glossary definition of delusion and the description of delusion in the account of schizophrenia (e.g., falsehood is regarded as a defining feature in the former, but not in the latter).

  5. This is a clear summary, Lisa! Your post was the best link I found after I came across this post: I wanted to understand how the definition of delusion changed in the DSM-5.

  6. The huge problem with the updated definition of delusion is that it would diagnose Christ as delusional because the updated definition does not require the belief to be false, nor does it require incorrect inference. Also the update does not even suggest the need for "incontrovertible and obvious proof" and only requires "conflicting evidence". The fact that Christ was not omnipresent (everywhere at once) would form contradictory evidence of Christ's claim to be God.

  7. and the bibliographical reference is...?

  8. Why are unwarranted (non-evidenced) inferences about reality that are rooted in religious faith somehow exempted from this category in DSM? Just because a delusion has a mass following or social support, that in no wise changes it's classification as psychological delusion.

    1. BINGO!
      1. Possibly DSM contributors might still be religious adherents, which can more easily lead to possible pro-religion bias.
      2. Some might perceive that religious faith based delusions were implanted (which is often the case), so they may think that the belief was not self-formed, yet that still does not excuse religious based delusion from common definitions:

      “A false belief or judgment about external reality, held despite incontrovertible evidence to the contrary, occurring especially in mental conditions.”

      “in psychology, a rigid system of beliefs with which a person is preoccupied and to which the person firmly holds, despite the logical absurdity of the beliefs and a lack of supporting evidence.”

      “belief in something that is not true”

      “beliefs held with conviction in spite of having little empirical support”

  9. ....I pray to God that there will be *NO* "DSM-6"....
    The DSM is really nothing more than a CATALOG of BILLING CODES.... Psychiatry is a pseudoscience, a drug racket, and a means of social control. It's 21st Century Phrenology, with potent neuro-toxins. Psychiatry has done, and continues to do, FAR MORE HARM than good.... NO DSM-6, please!

  10. Religion is a special problem as the beliefs are supported by the society (local or distributed) and are reinforced as terms of inclusion and exclusion - often with significant degrees of persecution. Hence, to hold or appear to hold religious delusions may be required to avoid severe treatment - up to and including being killed in some contexts, societies and states.

    A problem of religious delusion is that has often been indoctrinated from an early age, and it can be seen as a type of group or societal abuse against a type, characteristic or behaviour that is deemed anathema, heretical or sacrilegious. Thus there are strong forms of behavioural modification and punishment that are often imposed with extreme prejudice against individuals and types, and especially at times of group stress or tragedy. Highly irrational group behaviours and delusions are sometimes projected onto non-conforming types with attendant violence that is sanctioned by the group.

    So, religious delusions need to be characterized differently, and the group aspect and the severity of penalty for not conforming has to be taken into consideration when looking at individual beliefs and behaviours. (Survival and avoidance of extreme sanction are rational responses and reinforcement mechanisms of delusional beliefs.)


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