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Delusions: Understanding the Un-Understandable


Today's post is by Peter McKenna. He is a psychiatrist with some background in psychology, currently working full-time in research in Barcelona. He introduces his new book Delusions: Understanding the Un-understandable.



I have been interested in delusions for a long time and around five years ago decided to try and write a book on the topic. The result, for better or worse, is Delusions: Understanding the Un-understandable. The ‘un-understandable’ of the title references Jaspers’ contention that delusions are a) psychologically irreducible, ie they cannot be derived from other psychological experiences, either normal or abnormal; and b) are unmediated, ie they are immediate rather than being the product of reflection (for a good and concise account of Jaspers’ views, see Walker, 1991).

Apart from the work of Jaspers, who was a philosopher as well as a psychiatrist and whose thoughts on delusions have influenced successive generations of clinicians, I made a deliberate decision not to include any philosophy in the book. Nevertheless, the book may still intersect with the interests of followers of Imperfect Cognitions, as follows.

First of all, the book gives a detailed description of delusions as they are encountered in clinical practice. This is something I feel it is important to do, since it often seems like authors writing on delusions are trying to represent them as something they are not. It is not uncommon to hear statements (especially from psychologists) that there is something true at the heart of any delusion. In fact, as the book tries to show, delusions are a much more weird and wonderful phenomenon than this. Where is the hidden core of truth in John Nash’s (of A Beautiful Mind) letter turning down a job offer by a university on the grounds that he was about to take up a position as emperor of Antarctica? Or in the account of a patient who once told me that his brain had recently been removed from his body, flown to America, and taken to a recording studio on a wheelchair, where it took part in a recording session with a rap artist?

At various points the book addresses the important question of continuity between delusions and the beliefs expressed by normal or at least not frankly mentally ill people. While the continuum view of psychosis is currently very popular, I personally see many pitfalls and complexities with this view. Some well-known kinds of false beliefs that arise in healthy people – for example end of the world cults, witch-hunts and conspiracy theories – have in common that they are a) shared and b) impersonal. This is in contrast to delusions which are idiosyncratic and (in most cases at least) personal, ie focused on the person concerned or those close to him/her, rather than concerning the world at large. While I would certainly not deny that some normal people have psychotic-like experiences, the rates of 5-7% currently quoted by authors like Linscott and van Os (2013) are inflated by quite serious uncriticality of the approach used to elicit them. In fact, the case for a continuum is actually stronger for other kinds of abnormal beliefs, such as overvalued ideas and Beck’s depressive cognitions.




Two separate chapters review psychological theories of delusions. The results of this exercise are rather disappointing. Popular approaches such as probabilistic reasoning bias (‘jumping to conclusions’) and theory of mind abnormality are simply not supported by the available evidence. Specifically, while impairments are present in patients with schizophrenia/psychosis, in neither case do they correlate with scores on delusion scales. Rather more promising is the ‘two-factor’ theory, applied to the Capgras delusion and other so-called monothematic delusions in patients with neurological disease. The conclusion I reach in the book is that something like the two stage verification process of novel and unexpected events that Coltheart’s group and others have argued for, almost certainly must take place; nothing else seems capable of accounting for symptoms like confabulation and anosognosia for hemiplegia. The problem here, however, is an almost complete lack of formal experimental evidence.

Finally, if any of you would like an accessible guide to the currently extremely influential aberrant salience theory (and one that is entirely free of mathematical formulas), the book provides one. Is this theory supported? Well, it predicts that individuals with delusions (eg patients with schizophrenia, those with first-episode psychosis, those at high risk of developing psychosis) will show excessive activation in the ventral striatum, as salience gets inappropriately attributed to neutral stimuli. There is now ample evidence from fMRI studies using reward paradigms that activation in this brain region is abnormal in all these clinical groups. The only slight problem is that it the activation is reduced rather than increased. Maybe, though, there is a way round this problem…
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