Signs and symptoms of Fregoli's:

- delusions

- visual memory deficit

- deficit in self-monitoring

- deficit in self-awareness

- hallucinations

- deficit in executive functions

- deficit in cognitive flexibility

- history of seizure activity

- epileptogenic activity

The Fregoli delusion, or the delusion of doubles, 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 and is often of a paranoid nature, with the delusional person believing themselves persecuted by the person they believe is in disguise.

A person with the Fregoli delusion can also inaccurately recall places, objects, and events. This disorder can be explained by "associative nodes". The associative nodes serve as a biological link of information about other people with a particular familiar face (to the patient). This means that for any face that is similar to a recognizable face to the patient, the patient will recall that face as the person they know.

The Fregoli delusion is classed both as a monothematic delusion, since it only encompasses one delusional topic, and as a delusional misidentification syndrome (DMS), a class of delusional beliefs that involves misidentifying people, places, or objects. Like Capgras delusion, psychiatrists believe it is related to a breakdown in normal face perception.

Capgras delusion is a psychiatric disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member (or pet) has been replaced by an identical impostor. The Capgras delusion is classified as a delusional misidentification syndrome, a class of delusional beliefs that involves the misidentification of people, places, or objects. It can occur in acute, transient, or chronic forms. Cases in which patients hold the belief that time has been "warped" or "substituted" have also been reported.

The delusion most commonly occurs in patients diagnosed with paranoid schizophrenia, but has also been seen in patients suffering from brain injury and dementia. It presents often in individuals with a neurodegenerative disease, particularly at an older age. It has also been reported as occurring in association with diabetes, hypothyroidism, and migraine attacks. In one isolated case, the Capgras delusion was temporarily induced in a healthy subject by the drug ketamine. It occurs more frequently in females, with a female:male ratio of approximately 3:2. It is worth noting that there is historical and quite probably modern use of the Political decoy as well as Celebrity lookalike, and impersonation is used by criminals, as well. Although 'delusion' is defined as when a patient holds a false belief "in spite of incontrovertible evidence", such evidence is difficult to produce (in the case of Capgras symptoms), whether lookalikes exist or not. This does not deter psychiatrists from prescribing pharmaceutical chemicals for persons describing these situations with little, if any, investigation into the claims, though it seems even one actual encounter with a genuine impersonator (whether sinister or not) has a notably unnerving effect on future interactions with that actual person, and possibly leading to paranoia of others being impersonated. Carefully targeted identity thefts in this sense can cause quite a few real problems, ranging from confusion to petty theft, business and domestic situations going awry, sexual relationship sabotage or confusion (possibility of unplanned pregnancy and risk of STD exposure), and financial fraud.

The following two case reports are examples of the Capgras delusion in a psychiatric setting:

The following case is an instance of the Capgras delusion resulting from a neurodegenerative disease:

A monothematic delusion is a delusional 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). These disorders can occur within the context of schizophrenia or dementia or they can occur without any other signs of mental illness. 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, stroke, or neurological illness.

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.

The symptoms of the syndrome of subjective doubles are not clearly defined in medical literature, however, there are some defining features of the delusion:

- The existence of the delusion, by definition, is not a widely accepted cultural belief.

- The patient insists that the double he/she sees is real even when presented with contradictory evidence.

- Paranoia and/or spatial visualization ability impairments are present.

Similarities to other disorders are often noted in literature. Prosopagnosia, or the inability to recognize faces, may be related to this disorder due to the similarity of symptoms. Subjective doubles syndrome is also similar to delusional autoscopy, also known as an out-of-body experience, and therefore is occasionally referred to as an "autoscopic type" delusion. However, subjective doubles delusion differs from an autoscopic delusion: autoscopy often occurs during times of extreme stress, and can usually be treated by relieving the said stressor.

The syndrome of subjective doubles is usually accompanied by another mental disorder or organic brain syndrome, and may appear during or after the onset of the other disorder. Often, co-occurrence of subjective doubles with other types of delusional misidentification syndromes, especially Capgras syndrome, also occurs.

Several variations of the syndrome have been reported in literature:

- The doubles may appear at different ages of oneself.

- Some patients describe their double as both a physically and psychologically identical copy, rather than a purely physical copy. This is also known as clonal pluralization of the self, another type of delusional misidentification syndrome that may or may not be the same type of disorder (see #Controversy, below). In this case, depersonalization may be a symptom.

- Reverse subjective doubles occurs when the patient believes his/her own self (either physical or mental) is being transformed into another person. (see the case of Mr. A in #Presentation)

The delusions that fall under this category are:

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

- Fregoli delusion: 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 or double of him- or herself carrying out independent actions.

- Cotard delusion: 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: 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.

The delusion of negation is the central symptom in Cotard's syndrome. The patient afflicted with this mental illness usually denies his or her existence, the existence of a certain body part, or the existence of a portion of their body. Cotard's syndrome exists in three stages: (i) Germination stage—the symptoms of psychotic depression and of hypochondria appear; (ii) Blooming stage—the full development of the syndrome and the delusions of negation; and (iii) Chronic stage—continued, severe delusions along with chronic psychiatric depression.

The Cotard syndrome withdraws the afflicted person from other people due to the neglect of their personal hygiene and physical health. The delusion of negation of self prevents the patient from making sense of external reality, which then produces a distorted view of the external world. Such a delusion of negation is usually found in the psychotic patient who also presents with schizophrenia. Although a diagnosis of Cotard's syndrome does not require the patient's having had hallucinations, the strong delusions of negation are comparable to those found in schizophrenic patients.

Witzelsucht (from the German "witzeln", meaning to joke or wisecrack, and "sucht", meaning addiction or yearning) is a set of rare neurological symptoms characterized by a tendency to make puns, or tell inappropriate jokes or pointless stories in socially inappropriate situations. A less common symptom is hypersexuality, the tendency to make sexual comments at inappropriate times or situations. Patients do not understand that their behavior is abnormal, therefore are nonresponsive to others' reactions. This disorder is most commonly seen in patients with frontal lobe damage, particularly right frontal lobe tumors or trauma. The disorder remains named in accordance with its reviewed definition by German neurologist Hermann Oppenheim; its first description as the less focused "Moria" ("stupidity"), by German neurologist Moritz Jastrowitz, was in 1888.

Due to similarity of symptoms of the disorder to the mannerisms of Batman's arch-rival Joker, it is sometimes known as 'The Joker Syndrome'

Chronic hallucinatory psychosis is a psychosis subtype, classified under "Other nonorganic psychosis" by the . Other abnormal mental symptoms in the early stages are, as a rule, absent. The patient is most usually quiet and orderly, with a good memory.

It has often been a matter of the greatest difficulty to decide under which heading of the recognized classifications individual members of this group should be placed. As the hallucinations give rise to slight depression, some might possibly be included under melancholia. In others, paranoia may develop. Others, again, might be swept into the widespread net of dementia praecox. This state of affairs cannot be regarded as satisfactory, for they are not truly cases of melancholia, paranoia, dementia praecox or any other described affection.

This disease, as its name suggests, is a hallucinatory case, for it is its main feature. These may be of all senses, but auditory hallucinations are the most prominent. At the beginning, the patient may realize that the hallucination is a morbid phenomenon and unaccountable. They may claim to hear a "voice" speaking, though there is no one in the flesh actually doing so. Such a state of affairs may last for years and possibly, though rarely, for life, and the subject would not be deemed insane in the ordinary sense of the word.

It's probable, however, that this condition forms the first stage of the illness, which eventually develops on definite lines. What usually happens is the patient seeks an explanation for the hallucinations. As none is forthcoming he/she tries to account for their presence and the result is a delusion, and, most frequently, a delusion of persecution. Also, it needs to be noted that the delusion is a comparatively late arrival and is the logical result of the hallucinations.

"The following case describes a patient who was diagnosed with psychotic depression, bipolar disorder, and the syndrome of subjective doubles:"

Taken from Kamanitz et al., 1989:

"The following case describes a patient who has been diagnosed with schizoaffective disorder along with multiple delusional misidentification syndromes (subjective doubles, Capgras delusion, intermetamorphosis)":

Taken from Silva et al., 1994:

"The following case describes a patient who has been diagnosed with chronic paranoid schizophrenia and reverse subjective doubles:"

Taken from Vasavada and Masand, 1992:

Cotard delusion is a rare mental illness in which the affected person holds the delusional belief that they are already dead, do not exist, are putrefying, or have lost their blood or internal organs. Statistical analysis of a hundred-patient cohort indicates that the denial of self-existence is a symptom present in 69% of the cases of Cotard's syndrome; yet, paradoxically, 55% of the patients present delusions of immortality.

In 1880, the neurologist Jules Cotard described the condition as "Le délire des négations" ("The Delirium of Negation"), a psychiatric syndrome of varied severity. A mild case is characterized by despair and self-loathing, while a severe case is characterized by intense delusions of negation and chronic psychiatric depression. The case of Mademoiselle X describes a woman who denied the existence of parts of her body and of her need to eat. She said that she was condemned to eternal damnation and therefore could not die a natural death. In the course of suffering "The Delirium of Negation", Mademoiselle X died of starvation.

The Cotard delusion is not mentioned in either the "Diagnostic and Statistical Manual of Mental Disorders" (DSM) or the tenth edition of the "International Statistical Classification of Diseases and Related Health Problems" (ICD-10) of the World Health Organization.

Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou (in his book "The Delusional Misidentification Syndromes", Karger, Basel, 1986) for a group of delusional disorders that occur in the context of mental and neurological illness. They all involve a belief that the identity of a person, object, or place has somehow changed or has been altered. As these delusions typically only concern one particular topic, they also fall under the category called monothematic delusions.

This psychopathological syndrome is usually considered to include four main variants:

- The Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor.

- The Fregoli delusion is the belief that various people the believer meets are actually the same person in disguise.

- Intermetamorphosis is the belief that people in the environment swap identities with each other whilst maintaining the same appearance.

- Subjective doubles, described by Christodoulou in 1978 ("American Journal of Psychiatry" 135, 249, 1978), is the belief that there is a doppelgänger or double of him- or herself carrying out independent actions.

However, similar delusional beliefs, often singularly or more rarely reported, are sometimes also considered to be part of the delusional misidentification syndrome. For example:

- Mirrored-self misidentification is the belief that one's reflection in a mirror is some other person.

- Reduplicative paramnesia is 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 an identical-looking hospital in a different part of the country, despite this being obviously false.

- The Cotard delusion is a rare disorder in which people hold a delusional belief that they are dead (either figuratively or literally), do not exist, are putrefying, or have lost their blood or internal organs. In rare instances, it can include delusions of immortality.

- Syndrome of delusional companions is the belief that objects (such as soft toys) are sentient beings.

- Clonal pluralization of the self, where a person believes there are multiple copies of him- or herself, identical both physically and psychologically but physically separate and distinct.

There is considerable evidence that disorders such as the Capgras or Fregoli syndromes are associated with disorders of face perception and recognition. However, it has been suggested that all misidentification problems exist on a continuum of anomalies of familiarity, from déjà vu at one end to the formation of delusional beliefs at the other.

They are normally colorful, vivid images and occur during wakefulness, and predominately at night. Lilliputian hallucinations (also called Alice in Wonderland syndrome), hallucinations in which people or animals appear smaller than they would be in real life, are common in cases of peduncular hallucinosis. Most patients exhibit abnormal sleep patterns characterized by insomnia and daytime drowsiness. Peduncular hallucinosis has been described as a “release phenomenon” due to damage to the ascending reticular activating system, which is supported by the sleep disturbance characteristic of this syndrome. In most cases, people are aware that the hallucinations are not real. However, some people experience agitation and delusion and mistake their hallucinations for reality.

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 and, although rare, is most commonly associated with acquired brain injury, particularly simultaneous damage to the right cerebral hemisphere and to both frontal lobes.

Two types of confabulation are often distinguished:

- Provoked (momentary, or secondary) confabulations represent a normal response to a faulty memory, are common in both amnesia and dementia, and can become apparent during memory tests.

- Spontaneous (or primary) confabulations do not occur in response to a cue and seem to be involuntary. They are relatively rare, more common in cases of dementia, and may result from the interaction between frontal lobe pathology and organic amnesia.

Another distinction is that between:

- Verbal confabulations, spoken false memories are more common, and

- Behavioral confabulations, occur when an individual acts on their false memories.

Tactile hallucination is the false perception of tactile sensory input that creates a hallucinatory sensation of physical contact with an imaginary object. It is caused by the faulty integration of the tactile sensory neural signals generated in the spinal cord and the thalamus and sent to the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII). Tactile hallucinations are recurrent symptoms of neurological diseases such as schizophrenia, Parkinson's disease, Ekbom's syndrome and delerium tremens. Patients who experience phantom limb pains also experience a type of tactile hallucination. Tactile hallucinations are also caused by drugs such as cocaine and alcohol.

In both case studies, patients showed an altered sense of humor, mostly in regard to producing and appreciating humor. The right hemisphere is involved with processing speed and problem solving, which plays a role in humor processing. These patients have difficulty fully interpreting a joke's content, but can recognize the importance of the form of a joke. Patients with witzelsucht often find non sequiturs, slapstick humor, and puns funniest since these forms of humor do not require integration of content across sentences. In other words, the end of the joke is not dependent on the first part; one does not need to make a logical connection to understand humor. Patients show no change in understanding simple logic, and understand the importance of surprise in humor (hence why they choose slapstick humor instead of the “correct” punch line); however, once they have registered this surprise, they cannot connect the punch line to the body of the joke to fully appreciate the true humor behind the joke. Successful jokes require a juxtaposition of the sound and the meaning of words used to understand the punch line. However, patients with witzelsucht have difficulty connecting the two, resulting in an inability to appreciate humor.

Additionally, patients show no emotional reaction to humor, whether produced by themselves or others. This lack of responsiveness is due to dissociation between their cognitive and affective responses to humorous stimuli. That is, even when a patient understands that a joke is funny (based on quantitative brain activity), they do not respond with laughter, or even a smile. While they have grasped the cognitive basis of humor, they do not affectively respond. This also considered a cognitive component of empathy, affecting ability to take the perspective of others; hence why patients often do not respond to humor produced by other people.

Confabulation is distinguished from lying as there is no intent to deceive and the person is unaware the information is false. Although individuals can present blatantly false information, confabulation can also seem to be coherent, internally consistent, and relatively normal.

Most known cases of confabulation are symptomatic of brain damage or dementias, such as aneurysm, Alzheimer's disease, or Wernicke–Korsakoff syndrome (a common manifestation of thiamine deficiency caused by alcoholism). Additionally confabulation often occurs in people who are suffering from anticholinergic toxidrome when interrogated about bizarre or irrational behaviour.

Confabulated memories of all types most often occur in autobiographical memory and are indicative of a complicated and intricate process that can be led astray at any point during encoding, storage, or recall of a memory. This type of confabulation is commonly seen in Korsakoff's syndrome.

Peduncular hallucinosis (PH), or Lhermitte's peduncular hallucinosis, is a rare neurological disorder that causes vivid visual hallucinations that typically occur in dark environments, and last for several minutes. Unlike some other kinds of hallucinations, the hallucinations that patients with PH experience are very realistic, and often involve people and environments that are familiar to the affected individuals. Because the content of the hallucinations is never exceptionally bizarre, patients can rarely distinguish between the hallucinations and reality.

In 1922, the French neurologist Jean Lhermitte documented the case of a patient who was experiencing visual hallucinations that were suggestive of localized damage to the midbrain and pons. After other similar case studies were published, this syndrome was labeled "peduncular hallucinosis."

The accumulation of additional cases by Lhermitte and by others influenced academic medical debate about hallucinations and about behavioral neurology.

Lhermitte provided a full account of his work in this area in his book "Les hallucinations: clinique et physiopathologie," which was published in Paris in 1951 by Doin publishing.

Contemporary researchers, with access to new technologies in medical brain imaging, have confirmed the brain localization of these unusual hallucinations.

Memory distrust syndrome is a condition coined by Gísli Guðjónsson and James MacKeith in 1982, in which an individual doubts the accuracy of their memory concerning the content and context of events of which they have experienced. Since the individual does not trust their own memory, they will commonly depend on outside sources of information rather than using their ability for recollection. Some believe that this may be a defense or coping mechanism to a preexisting faulty memory state such as Alzheimer's disease, amnesia, or possibly dementia.

The condition is generally considered to be related to source amnesia, which involves the inability to recall the basis for factual knowledge. The main difference between the two is that source amnesia is a lack of knowing the basis of knowledge, whereas memory distrust syndrome is a lack of believing the knowledge that exists. The fact that an individual lacks the trust in their own memory implies that the individual would have a reason or belief that would prevent them from the trust that most of us have in our recollections. Cases concerning memory distrust syndrome have led to documented false confessions in court cases.

About 7% of individuals with Parkinson's disease also experience mild or severe types of tactile hallucinations. Most of these hallucinations are based on the sensation of a particular kind of animal. Several case studies were conducted by Fénelon and his colleagues on parkinson's patients that had tactile hallucinations. One of his patients described that he sensed "spiders and cockroaches chewing on his lower limb" which was rather painful. Several other patients felt that there was a parasitic infestation of their skin which caused lesions on their skins due to the obsessive need of itching. Fénelon also analyzed the particular types of tactile hallucinations experienced, the timing of such experience and certain drugs that could eliminate such experience. It was concluded that patients with both Parkinson's disease and tactile hallucinations not only experienced sensations elicited by insects under their skin but also by vivid tactile sensations of people. These hallucinations were aggravated during evening times due to altered arousal states and were alleviated by dopaminergic treatment such as the intake of clozapine. The study also explains that the pathophysiology of tactile hallucinations is uncertain, however, such hallucinations can be attributed to narcoleptic rapid eye movement sleep disorders due to its concordance with visual hallucinations. Moreover, it emphasizes that individuals who have had Parkinson's for a longer period of time have a more severe form of tactile hallucinations than with individuals who have succumbed to this disease for just a short period of time.

Clinical drugs used as an antiparkinsonian agent such as Trihexyphenidyl are known to create tactile hallucinations in parkinson patients.

Ideas of reference and delusions of reference describe the phenomenon of an individual's experiencing innocuous events or mere coincidences and believing they have strong personal significance. It is "the notion that everything one perceives in the world relates to one's own destiny".

In psychiatry, delusions of reference form part of the diagnostic criteria for psychotic illnesses such as schizophrenia, delusional disorder, bipolar disorder (during the elevated stages of mania), as well as schizotypal personality disorder. To a lesser extent, it can be a hallmark of paranoid personality disorder. Such symptoms can also be caused by intoxication, especially with hallucinogens or stimulants like methamphetamine.

Diagnosis of a specific type of delusional disorder can sometimes be made based on the content of the delusions. The "Diagnostic and Statistical Manual of Mental Disorders" (DSM) enumerates seven types:

- Erotomanic type (erotomania): delusion that another person, often a prominent figure, is in love with the individual. The individual may breach the law as he/she tries to obsessively make contact with the desired person.

- Grandiose type: delusion of inflated worth, power, knowledge, identity or believes themself to be a famous person, claiming the actual person is an impostor or an impersonator.

- Jealous type: delusion that the individual's sexual partner is unfaithful when it is untrue. The patient may follow the partner, check text messages, emails, phone calls etc. in an attempt to find "evidence" of the infidelity.

- Persecutory type: This delusion is a common subtype. It includes the belief that the person (or someone to whom the person is close) is being malevolently treated in some way. The patient may believe that he/she has been drugged, spied upon, harassed and so on and may seek "justice" by making police reports, taking court action or even acting violently.

- Somatic type: delusions that the person has some physical defect or general medical condition

- Mixed type: delusions with characteristics of more than one of the above types but with no one theme predominating.

- Unspecified type: delusions that cannot be clearly determined or characterized in any of the categories in the specific types.

Thought insertion is defined by the ICD-10 as feeling as if one's thoughts are not one's own, but rather belong to someone else and have been inserted into one's mind. The person experiencing thought insertion will not necessarily know where the thought is coming from, but is able to distinguish between their own thoughts and those inserted into their minds. However, patients do not experience all thoughts as inserted, only certain ones, normally following a similar content or pattern. This phenomenon is classified as a delusion. A person with this delusional belief is convinced of the veracity of their beliefs and is unwilling to accept such diagnosis.

Thought insertion is a common symptom of psychosis and occurs in many mental disorders and other medical conditions. However, thought insertion is most commonly associated with schizophrenia. Thought insertion, along with thought broadcasting, thought withdrawal, thought blocking and other first rank symptoms, is a primary symptom and should not be confused with the delusional explanation given by the respondent. Although normally associated with some form of psychopathology, thought insertion can also be experienced in those considered nonpathological, usually in spiritual contexts, but also in culturally influenced practices such as mediumship and automatic writing.

Examples of thought insertion:

"She said that sometimes it seemed to be her own thought 'but I don't get the feeling that it is'. She said her 'own thoughts might say the same thing', 'but the feeling isn't the same', 'the feeling is that it is somebody else's'"

"I look out the window and I think that the garden looks nice and the grass looks cool, but the thoughts of Eamonn Andrews come into my mind. There are no other thoughts there, only his. He treats my mind like a screen and flashes thoughts onto it like you flash a picture"

"The subject has thoughts that she thinks are the thoughts of other people, somehow occurring in her own mind. It is not that the subject thinks that other people are making her think certain thoughts as if by hypnosis or psychokinesis, but that other people think the thoughts using the subject's mind as a psychological medium."