Friday, 7 June 2013

Delusions in the DSM 5

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...

9 comments:

  1. Hello Lisa! Thanks so much for providing the DSM-5 definition and your observations, I am having trouble getting a hold of the new DSM text and this helps a lot. Just a question: could you provide the full text? I am a little curious to know what is it that you suppressed in your quote. A page reference for the definition would also be very helpful. Thanks a lot in advance.

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  2. 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.

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  3. In case somebody out there is interested in the full definition, here it is:

    "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). Persecutory delusions (i.e., the belief that one is going to be harmed, harassed, and so forth by an individual, organization, or other group) are most common. Referential delusions (i.e., belief that certain gestures, comments, environmental cues, and so forth are directed at oneself) are also common. Grandiose delusions (i.e., when an individual believes that he or she has exceptional abilities, wealth, or fame) and erotomanic delusions (i.e., when an individual believes falsely that another person is in love with him or her) are also seen. Nihilistic delusions involve the conviction that a major catastrophe will occur, and somatic delusions focus on preoccupations regarding health and organ function.

    "Delusions are deemed bizarre if they are clearly implausible and and not understandable to same-culture peers and do not derive from ordinary life experiences. An example of a bizarre delusion is the belief that an outside force has removed his or her internal organs and replaced them with someone else's organs without leaving any wounds or scars. An example of a nonbizarre delusion is the belief that one is under surveillance by the police, despite a lack of convincing evidence. Delusions that express a loss of control over mind or body are generally considered to be bizarre; these include the belief that one's thoughts have been "removed" by some outside force (thought withdrawal), that alien thoughts have been put into one's mind (thought insertion), or that one's body or actions are being acted on or manipulated by some outside force (delusions of control). 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."

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  4. 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?

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    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.

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  5. 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.

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  6. The definition of delusion since the DSM-III has appeared in the "Glossary of Technical Terms". Did you notice that the "Glossary" in the DSM-5 gives the same definition that has come down since the DSM-IV?

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    1. 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).

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  7. This is a clear summary, Lisa! Your post was the best link I found after I came across this post: http://plato.stanford.edu/entries/belief/#2.7 I wanted to understand how the definition of delusion changed in the DSM-5.

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