Delusions

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/evidence to the contrary" (DSM-IV, 2000)

OR

SM V: 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).[...] These 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 this 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

Problems

With DSM IV definition (Coltheart, 2007):

• Couldn’t belief in something true be delusional if
  you held the belief for the wrong reasons?

• Does a delusion have to be a belief – can’t it be
  something you imagine or perceive?

• Does the belief have to concern external reality-
  what about internal states?

• Can’t a belief which is shared by everyone you
  know still be delusional?

Clinical delusions

A diagnosis of this occurs when a person has one or more non-bizarre (situations that can take place in real life, although not real but are possible) delusional thought for one month or more, that has no explanations other than a psychological basis

Capgras delusion

The delusion that familiar people have been
replaced by impostors.

• May extend to familiar objects.

• Tends to be specific to visual encounters rather
  than other modalities.

Mirror-sign delusion

• Inability to recognise oneself in the mirror.

• May be associated
  with dementia.

Fregoli delusion

• Unfamiliar people are actually people you
  know who have disguised themselves. They
  have bad intentions towards you.

• ‘People I know are following me around, but
  in disguise, so I can never recognize them’
  (from Coltheart, 2007)

Constituents

(/Explanation Of a delusion)

• Some sort of deficit which changes the way our minds or bodies work

• A refusal to reject beliefs arising from the deficit

• Frequent encapsulation of the delusion - beliefs are not acted on; missing people are not searched for, people claim to be dead but still walk around and talk... Casts doubt on the notion of a consistent 'web of belief'

• Delusions may come and go

Bayesian inference

Goal: optimise beliefs about parameter of interest.
→ What is the chance of rolling a six (Θ)?

• In a graph (showing (bell) curve distributions) we can quantify our beliefs about Θ

(tbh I don’t know much about this. image is meant to help but idk if it does)

Neurobiology

(Relations to)

• NMDA receptors play a key role
  in controlling synaptic gain

• NMDA-R dysfunction has been
  proposed as a primary pathology
  in schizophrenia (e.g. effect of
  ketamine)

• Hypothesis: NMDA-R
  abnormalities lead to aberrant
  signalling of precision, and
  therefore pathological inference

Explanation

(General)

• Propose one general deficit

• But how does this relate to specific
  delusions? (And those not found in
  psychosis?)

• Also Functional disorders…