A monothematic delusion is a

delusion A delusion is a fixed belief that is not amenable to change in light of conflicting evidence. As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, hallucination, or some other m ...

al state that concerns only one particular topic. This is contrasted by what is sometimes called ''multi-thematic'' or ''polythematic'' delusions where the person has a range of delusions (typically the case of

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

). These disorders can occur within the context of schizophrenia or

dementia Dementia is a syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...

or they can occur without any other signs of

mental illness A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is ...

. When these disorders are found outside the context of mental illness, they are often caused by organic dysfunction as a result of

traumatic brain injury A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity ranging from mild traumatic brain injury (mTBI/concussion) to severe traumati ...

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

, or

neurological illness Neurological disorders represent a complex array of medical conditions that fundamentally disrupt the functioning of the nervous system. These disorders affect the brain, spinal cord, and nerve networks, presenting unique diagnosis, treatment, and ...

. People who experience these delusions as a result of organic dysfunction often do not have any obvious intellectual deficiency nor do they have any other symptoms. Additionally, a few of these people even have some awareness that their beliefs are bizarre, yet they cannot be persuaded that their beliefs are false.

Types

Some delusions that fall under this category are: *

Capgras delusion Capgras delusion or Capgras syndrome is a psychiatric disorder in which a person holds a delusion that a friend, spouse, parent, other close family member, or pet has been replaced by an identical impostor. It is named after Joseph Capgras (1873 ...

: the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor. *

Fregoli delusion The Fregoli delusion (or Fregoli syndrome) is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise. The syndrome may be related to a brain lesion an ...

: the belief that various people whom the believer meets are actually the same person in disguise. * Intermetamorphosis: the belief that people in one's environment swap identities with each other while maintaining the same appearance. * Subjective doubles: a person believes there is a

doppelgänger A doppelgänger ( ), sometimes spelled doppelgaenger or doppelganger, is a ghostly double of a living person, especially one that haunts its own fleshly counterpart. In fiction and mythology, a doppelgänger is often portrayed as a ghostly or p ...

or double of themselves carrying out independent actions. *

Cotard delusion Cotard's syndrome, also known as Cotard's delusion or walking corpse syndrome, is a rare mental disorder in which the affected person holds the delusional belief that they are deceased, do not exist, are putrefying, or have lost their blood or ...

: the belief that oneself is dead or does not exist; sometimes coupled with the belief that one is putrefying or missing internal organs. * Mirrored-self misidentification: the belief that one's reflection in a mirror is some other person. *

Reduplicative paramnesia Reduplicative paramnesia is the delusional belief that a place or location has been duplicated, existing in two or more places simultaneously, or that it has been 'relocated' to another site. It is one of the delusional misidentification syndromes ...

: the belief that a familiar person, place, object, or body part has been duplicated. For example, a person may believe that they are, in fact, not in the hospital to which they were admitted, but in an identical-looking hospital in a different part of the country. * Somatoparaphrenia: the delusion where one denies ownership of a limb or an entire side of one's body (often connected with stroke). Note that some of these delusions are sometimes grouped under the umbrella term of

delusional misidentification syndrome Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou (in his book ''The Delusional Misidentification Syndromes'', Karger, Basel, 1986) for a group of four delusional disorders that occur in the context of mental i ...

Causes

Current

cognitive neuropsychology Cognitive neuropsychology is a branch of cognitive psychology that aims to understand how the structure and function of the brain relates to specific psychological processes. Cognitive psychology is the science that looks at how mental processes ...

research points toward a two-factor cause of monothematic delusions. The first factor is an anomalous experience, often due to a neurological defect. The second is an impairment of the belief formation cognitive process. For example, the first factor in

is an impairment in how the brain recognizes a familiar face – specifically, how it cross-references one’s

feelings According to the '' APA Dictionary of Psychology'', a feeling is "a self-contained phenomenal experience"; feelings are "subjective, evaluative, and independent of the sensations, thoughts, or images evoking them". The term ''feeling'' is closel ...

toward the person. A patient with this disorder can recognize a loved one’s face, but seeing it does not elicit the expected emotional reaction. The patient’s mind interprets this as seeing a stranger, who merely looks like their loved one. The second factor, an impairment in the belief formation cognitive process, remains unclear as the process itself is not well-understood. And while the two-factor hypothesis is currently the dominant model, there are alternatives which do not involve a second factor. There is evidence that delusional people are more prone to jumping to conclusions, predisposing them to accept anomalous experiences as real and make snap judgments about them. Studies have also shown that such individuals are more prone to making errors due to matching bias, showing an higher than average tendency to seek confirmation for existing beliefs as opposed to testing how well they stand up to being challenged. These judgment biases help explain how delusion-prone people adopt and hold firm to extreme beliefs, though researchers disagree about whether they are sufficient explanation. Some posit that patients must have an additional neurological defect that affects their belief formation process. This defect is largely speculative, but would likely be located in the right hemisphere of the brain.

References

External links

The Belief Formation Project
a project of the Macquarie Centre for Cognitive Science, which uses research on delusions with the aim of developing a cognitive model of beliefs (link accessed on February 1, 2016) {{Delusion Psychosis Delusional disorders Delusions

Types

Causes

See also

References

External links