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Flashcards in Neuropsychiatry Deck (12):

Describe the rational for the 2-factor theory of delusional belief, then define the model.

Rational: The model needs to answer two questions:

(1) what suggested the idea that forms the basis of a/the delusions
(2) what prevented the proper evaluation of this idea (why wasn't it promptly rejected).

The 2-factor theory of delusional belief therefore suggests:

Factor 1: A neuropsychological impairment that explains the CONTENT of the/a delusion, which is different for different delusions.

Factor 2: A neuropsychological impairment that explains the MAINTENANCE of the delusions, which is the same for all delusions. (i.e., damage to the putative belief evaluation system located in the right hemisphere)


What are some problems with the following DSM-V definition of 'delusions':

"A false belief based on incorrect inference about external reality that is firmly held despite what constitutes incontrovertible & obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the persons culture or subculture"

[Notes from reading]
1. couldn't a true belief be a delusion, so long as the believer had no good reason for holding the belief.
2. Do delusions really have to be BELIEFS - might they not instead be the imaginings that are mistaken for beliefs by the imaginer.
3. Must all delusions be based on inference?
4. Aren't there delusions that are not about external reality? e.g., "i have no bodily organs" or "my thoughts are not mine bit are inserted into my mind by others" are beliefs expressed by some people with schizophrenia, yet are not about external reality; aren't these nevertheless still delusional beliefs?
5. Couldn't a belief held by all members of one's community still be delusional?

[Artemis Lecture notes:]

'False belief' - Delusions can be based on 'true beliefs', if the 'true belief' is held with a conviction not warranted by the degree of facts/information the person actually has (e.g., spouse is cheating may be true, but person may hold the belief strongly without good evidence for it).

'Inference' - may not be based on inference at all - mistaken imagining.

'External' - can be internal

'Firmly held' - not always the case, delusions wax and wane

'Incontrovertible and obvious proof' - many delusions involve subjective evaluation

' Not one ordinarily accepted by other members of the person's culture or subgroup' - can be group delusions (cults!).


Define delusions (3-factors definition, NOT DSM-V definition!)

A belief --> delusions when:

Incomprehensibility = sheer fantastical delusional content held despite contextual lack of evidence.
Incorrigibility = Resistance to counter evidence/argument
Unwarranted subjective conviction = The belief/delusions has the quality of being a 'self-evident' truth.


What are some criticisms of the 2-factor model of delusions? [and some counter-comments!]

1. If factor2 leads to maintenance of delusions via failure to reject beliefs which should be rejected - why are there cases of people with only one-few delusional beliefs. [perhaps delusions only arise when there is also a factor 1 ]

2. Why do delusions fluctuate. [may be a tendency for people to offer more counter-evidence and criticism of a delusional belief the more explicit and obvious it is, which may lessen the delusional belief ...and subsequently the counter-evidence provided by others..allowing it to increase again!]. The belief evaluation system is not BROKEN, but is weakened, such that in highly favourable circumstances one is able to reject delusions temporarily.

3. Why are some delusions (E.g., capgras) only about a few people (e.g., belief that mum has been replaced by an imposter, but does not hold this belief about other people) [for capgras, may relate to the proposed factor1, that is only occurs for people to which the individual normally has a high autonomic response for]

4. Scope of the theory -- only really explains monothematic delusions. [I got nothing!]


Define: mirror self-misidentification delusions

and a/the proposed factor 1

Can't recognise a reflection of ones self in the mirror as being ones self. "The person in the mirror is not me, but some stranger who looks like me!"

Factor 1: mirror agnosia (losing knowledge of what a mirror is and how it works) or impairment in face perception.

[From reading:]

Case T.H mirror agnosia - seated in front of a mirror and, as he was looking into it, objects were held up being him so that their reflections were visible in the mirror, and he was asked to grasp each object. Instead of reaching behind himself over the appropriate shoulder, he invariably reached toward the mirror to try to grasp the object, his hand hitting the surface or going round behind it. He could not correct this behaviour. Thus for him a mirror was a window, or an aperture in a wall in front of him.

Case FE face perception - marked disorder of face processing. He could name only 1 of a set of 51 photographs of famous faces, was poor at face-matching tasks, and frequently mis-identified photographs of strangers as being photographs of people personally known to him.


Define: Somatoparaphrenia

and a/the proposed factor 1

Disownment of a limb/extremity (e.g., a paralysed arm)

Factor 1: limb paralysis (reduced/absent sensation)

[From the reading:]

Some patients with right-hemisphere lesion that has caused paralysis of left limbs will deny ownership of these limbs, attributing ownership of the limbs to someone else (usually the examiner): clearly a delusion belief.

Studies of 65 patients undergoing pre-operative evaluation for intractable epilepsy who received intracarotid amobarbitol injections to non-language dominant hemisphere - during the period immediately after the injection, when there was paralysis of the contralateral arm, the patient's paralysed arm was placed in the visual hemifield contralateral to the affected hemisphere and the patient was asked 'whose hand is this?" 88% said it was someone else's hand!. when asked 'what is this' '75% it was someone else's hand, 25% said it was their hand. ....Suggestion that Factor 2 (maintenance of delusion) localised to right hemisphere.


Define: Capgras Delusion

and a/the proposed factor 1

Belief that a familiar person/people has been replace by an imposter (can also affect other things e.g, one's house)

Factor 1: reduced autonomic response to familiar faces, when normally autonomic responses would heighten when seeing a familiar person.

[from the reading:]

Ellis and Young (1990) proposed that, based on the dual-route model of normal face processing according to which perception of a familiar face evokes conscious recognition of the identity of the face via a ventral route and an affective response to the face via a dorsal route. They proposed that the cause of Capgras delusion is neuropsychological damage to the second of these two routes. In such a condition there would be conscious recognition of the identity of a face by absence of the affective response that characteristically accompanies the perception of a familiar face, especially the face of someone emotionally close to the viewer. When patients find themselves in such conflict (that is, receiving some information which indicates the face in front of them belongs to X, but not receiving confirmation of this), they may adopt some sort of rationalizations strategy in which the individual before them is deemed to be an imposter, a dummy, a robot, or whatever extant technology may suggest.

This theory was tested by Ellis, Young, QUayle, and De Pauw (1997). Their experiment measured autonomic responses to pictures of unfamiliar and familiar (Famous) faces using the skin conductance response (SCR) as an index. Healthy control subjects showed substantial autonomic responses to unfamiliar faces and much larger response to familiar than unfamiliar faces. Five ps with capgras syndrome showed essentially no autonomic responses to faces and certainly no greater response when the faces were familiar than when they were unfamiliar (replicated by Hirstein and Ramachandran 1997)


Define: Cotard Delusion

and a/the proposed factor 1

Belief that ones self is dead

Factor 1: General autonomic un-reactivity


Define: Fregoli Delusion

and a/the proposed factor 1

Belief that strangers are familiar people in disguise. (i.e opposite to capgras!)

Factor 1: Increase in autonomic response to strangers


Define: Alien Control Delusions

and a/the proposed factor 1

Belief that other people can cause one's limbs to move when one did not intend them to move. (mind control).

Factor 1: altered sensory feedback to self-generated action.


What has been proposed as factor 2?

A neuropsychological impairment that explains the MAINTENANCE of the delusions, which is the same for all delusions. Appears to be 'localised' to the right hemisphere, specific studies have linked this factor with:


- right fronto dorsolateral infarct
- right temporal parietal infarct
- right temporal-parietal contusions and bilateral frontal damage
- right parietal lobe


What is cognitive neuropsychiatry?

A field of cognitive psychology which seeks to learn more about the normal operation of high-level aspects of cognition such as belief formation, reasoning, decision making, theory of mind, and pragmatics by studying people in whom such processes are abnormal.