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…