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Studies of Delusional Jealousy


Prevalence of delusional jealousy to some extent depends on the observer. Of 14300 patients admitted to a German hospital between 2000 – 2008, 0.5% had delusional jealousy. Most of these patients had psychosis and were often male (Soyka 2011). When a retrospective chart analysis of patients in Munich was looked at, there was a prevalence of 1.1% of delusional jealousy, though there were slightly more women (Soyka 1991). Amongst an elderly population in Hong Kong the prevalence was 1.4% (Chiu 1995). Delusional jealousy has been found in the same-sex relationship population (Aldana 2003).


A study looking at delusional jealousy used the morbid jealousy database containing case histories from 1942–2002. Jealousy was classed in different ways, probably different to how we do it today. About 33% had delusional disorder jealous type, 7% had morbid jealousy and 4% obsessional jealousy. To be diagnosed with delusional disorder – jealous type there must be no significant hallucinations, behaviour must not be bizarre, mood must be normal and, if not, it must be brief and present only in the delusional period as well as there being an absence of a medical condition or substance abuse. Once these are considered, only 4% met the criteria for delusional disorder, but by loosening these criteria we find higher levels of delusional jealousy (65.9%) (Easton 2008). Using the morbid jealousy database, males were upset by sexual infidelity and women by emotional infidelity. Thirty-six cases described the supposed rival, with men reporting significantly more concerned about the rival’s status / resources and women more concerned about rival youth / attractiveness (Easton 2007).


A hypothesised involvement of gonadal hormones may lie behind delusions of jealousy (and somatic) being commoner in post-menopausal women with delusional disorder (Gonzalez Rodriguez 2022). Oxytocin given intra-nasally may allow us to see our partner as more attractive. Given to women it may result in attraction to faithful males, whilst in males it increases attraction for unfaithful women (Zheng 2021). Parkinsonian drugs that alter dopamine levels are associated with delusional jealousy (Arjmand 2021), e.g., Ropinirole (Pal 2012). In a series of patients with Parkinsons disease, the presence of dopamine agonists was associated with a greater risk of delusional jealousy (OR=18.1, p= <0.001) (Poletti 2013). Unfortunately, removal of dopamine agonists does not necessarily result in the disappearance of the symptom.


Alterations in fronto-striatal circuits, the ventral medial prefrontal area, thalamus, insula and amygdala may be involved in delusional jealousy. Healthy jealousy is associated with increased activity in the basal ganglia and the vmPFC (Zheng 2021). A meta-analysis of 20 patients identified right hemisphere damage. Damage is often found in the right frontal (Arjmand 2021, Luaute 2008). Delusional jealousy has been associated with strokes (Blasco-Fontecilla 2005). A 49-year-old man with widespread brain infarcts developed delusions of jealousy toward his wife about a year later (Loizou 1982). A 25-year-old woman developed Othello syndrome several years after her stroke (Westlake 1999). It has been linked to strokes in the territory of the middle cerebral artery on the right (Chae 2006), in the right basal ganglia (Wong 1997). But the left hemisphere has a part to play also, there have been left side strokes that cause Othello (Kuruppuarachchi 2011).


A 70-year-old woman with poorly differentiated carcinoma in the left hilar lung region, with accompanying bony metastases but no cerebral involvement, developed Othello syndrome (Egan 1996). A 39-year-old patient with a learning disability, epilepsy and left-side hemiplegia after a RTA, developed jealousy after being with another women and having two children with her (Cooper 1993).


Many cases of morbid jealousy are associated with excessive alcohol consumption. A review of 207 patients with alcohol dependence found that 71 were morbidly jealous; 20 displayed the jealousy only while drunk. Interestingly, the mean duration of alcohol intake before the appearance of jealousy was longer in those who expressed it when drunk (7.6 versus 3.6 years, t=2.7, p<0.01). Pre-existing delusional disorder was equally common in the jealous and non-jealous group. The jealous group had six with delusional disorder unspecified and nine with delusional disorder – jealous type (Michael 1995, Byrne 1989).


In terms of treatment a retrospective review of 32 patients with delusional jealousy found that antipsychotics and antidepressants worked in about 60% (Liu 2018). Tiapride has helped some (Mukai 2003, Mukai 2004).


A review of patients with delusional jealousy in Sri Lanka found an age range of 24 – 73 yrs, with a slightly smaller range in females. The age differences between patients and their partners were 0 to 38 yrs. About two thirds were married, over 90% had children. About two thirds of patients and their partners were in employment (De Silva 2021). Cultural differences in the prevalence and expression of delusional jealousy have been noted. When looking at schizophrenics in Korea, Taiwan and China, delusional jealousy was commonest in the Koreans, with the frequency of delusional jealousy reducing in Taiwan since the 1950s. Also, delusions of being raped were commonest amongst Koreans (Kim 2001; Kim 2006).


An important factor to consider here is that from a psychopathological point of view, there are various non-delusions forms of jealousy, which are found in other disorders. This applies to most if not all delusions in general. What are the differences between normal, over-valued, depressive, obsessional and delusional jealousy? Of 245 students who replied to the Questionnaire on the Affective Relationships; jealousy scores were higher in the obsessional, but 10% had clinically non-relevant jealousy symptoms (Marazziti 2003).


Obsessional Jealousy. The main difference here is that patients know their concerns may be false, but they cannot stop the behaviours (Batinic 2013). When the Questionnaire on the Affective Relationships (which has one question related to infidelity) were given to healthy controls, patients with OCD and jealous healthy controls found the OCD to have more jealousy concerns (Marazziti 2003). It can respond to standard treatments for OCD. 4 out of 6 patients with obsessional elements to their jealousy responded to a SSRI (Stein 1994). A 34-year-old responded to fluoxetine 60mg (Lane 1990). A case series of 4 with morbid jealousy that was felt to relate to OCD, found 3 responded to psychotherapy (Cobb 1979). It is said that obsessional jealousy may be commoner in depression (Singh 2017).


Studies in evolution and jealousy


Now to my mind if makes sense that if jealousy has a role in sexual selection, i.e. making a person more or less likely to have children, then it must have greatest effect during a person’s fertile period such as when young. But in a study comparing an older sample with a much younger sample from a previous study, it was found that the older males were still more likely to be distressed by their partner’s sexual infidelity, but the effect sizes were smaller. Interestingly, when younger and older women were compared it was found that the older women were more distressed by their partner’s sexual infidelity, and younger women more by their emotional infidelity. The authors speculated that older women were less likely to have dependent children and that losing a partner is more damaging to their future, hence the concern with sexual infidelity. But an alternative view is that as young men tend to stray more often, they are more likely to return to their partner than a comparable elderly man. An elderly man who strays may be more likely to leave and hence older women being upset in response to sexual infidelity may help to preserve the relationship, although of course men are fertile for a lot longer than women (Shackelford 2004c).


Differences in the experience of jealousy include the previously mentioned finding that men find sexual infidelity more upsetting while women find emotional infidelity more distressing. Women are distressed more by other attractive women, are more likely to show mate guarding behaviours if their partners have a lot of resources, and they are more likely to process and recall cues of emotional infidelity. Men are distressed more by other males who are resource rich and they show higher levels of mate guarding if their partner is attractive or ovulating. Men are also more likely to process and recall cues of sexual infidelity, to be more unforgiving, or to end a relationship if their partner commits a sexual indiscretion (Buss 2005).


Although not a direct test of evolutionary theories, one interesting study was performed that might illustrate the importance of resources in elicitation of jealousy. This involved participants imagining their partners interacting with their ex-partner, and it was found that there were higher levels of anxiety when people were eating together than if they were just involved in face-to-face contact (Kniffin 2012).


Trivers theory of parental investment says that as women invest more in children, they are the choosier of the sexes. Hence it may make sense to make them the object of jealousy to prevent future infidelity, i.e., men focus on women to stop them from straying while women focus on the female rival. This means males are concerned about sexual infidelity and females by emotional infidelity (Schützwohl 2008).


Before going on, it is important to say that jealousy is experienced by both men and women and there are similarities in the experience of jealousy as well as differences. These similarities include being alerted to a potential threat to a relationship, especially if good looking rivals are around, and it serves (in part) to prevent infidelity and loss of the partner becoming distressed by emotional and sexual infidelity (Buss 2005).


The gender-specific patterns of jealousy have tended to be found in the forced choice paradigms, whereas in the continuous measures the results are more equivocal. Some have suggested that there is a gender-neutral response to find sexual infidelity more jealousy-provoking. And as continuous measures lend themselves to automatic processing, then this unconscious response to sexual infidelity is found. The forced choice paradigm forces people to make a deliberate choice, using conscious decisions influenced by other factors. Results in forced choice paradigms for men agree with the results of the unconscious information processing but in females these deliberate choices override this simple automatic, unconscious processing (Schützwohl 2008b, DeSteno 2002). Other studies have shown inconsistent sex differences in response to infidelity (Strout 2005; Schützwohl 2007).


DeSteno 2002 attempted to investigate jealousy responses using differing methodologies. The first experiment used a forced choice method. This found distress in the expected gender related pattern. For the continuous response tests both genders reported being ‘more upset’, ‘less relieved’, ‘more jealous (trend for F>M)’ about sexual infidelity, while females reported ‘greater distress’ for both types of infidelity. In essence, the results indicated that gender did not explain the differences in response to sexual and emotional infidelity (DeSteno 2002).


Most studies use simultaneous presentation of jealousy-related stimuli, but this may not be a realistic presentation of stimuli. If jealousy involved innate evolutionary modular processes, their function would remain unchanged under a cognitive load as conscious control is not required. Hence if performance worsened under cognitive load, we may not be looking at evolved modules. A group of students were assessed for responses to jealousy with some under a cognitive load. Women more distressed by sexual infidelity under cognitive load, but by emotional infidelity when not under a cognitive load, i.e., when required to be quick males and females were distressed by sexual infidelity more than emotional infidelity (DeSteno 2002). But a re-analysis of their results found that the gender difference under the cognitive load was reduced and not removed under conditions of cognitive load (Schützwohl 2008).


DeSteno’s study has been criticised because choices re sexual infidelity often came first, with one of the cognitive tasks being longer than the others, may have forced people to choose the first option because it was simpler. It has also been suggested that evolutionary modules will only operate automatically with the correct input signals, but DeSteno used the digit string memory task which may have interfered with the inputs needed for jealousy-related modules to operate, hence preventing the jealousy-related modules from being activated.


The study was repeated but the cognitive load was either related or unrelated to jealousy. When there was no cognitive load, people had 10s to answer forced choice questions to force jealousy-related modules to become active. Under both cognitive conditions, significantly more males than females felt jealous on sexual infidelity, but results were marginally significant for the digit load condition. Sexual infidelity was more likely to be selected if it was the first choice but only in the digit condition. Males were more likely to be upset by sexual infidelity in the no cognitive load condition, while females were more upset by emotional infidelity in all cognitive load conditions (Schützwohl 2008). This was taken to support evolutionary models of jealousy, to argue against males and females having the same default response to infidelity. It also argues against forced choices inducing elaborate processing as there is evidence that males and females respond faster to cue indicating sexual and emotional infidelity.


Some have said that study participants come with social conditioning, hence any gender differences in jealousy simply reflect prevailing social norms. It may be that if people feel one type of infidelity is present, then the other is assumed to be present which could lead to a focus on events that may lead to both. Social comparison theory says many events trigger jealousy, with gender differences due to gender-specific cognitive appraisals. Some feel that the attitude to romance is just as influential as gender and this was looked at in one study that looked at jealousy amongst different ethnic groups. People were categorised by skin colour, then asked to image a relationship and sexual or emotional infidelity with someone of the same or other ethnic group (Bassett 2005, DeSteno 2002):


  • Both genders (F>M) were more distressed by sexual infidelity regardless supposed rival race.

  • There was more anger over sexual infidelity, regardless of race.

  • Black and white women showed more anger for sexual infidelity. White males were angrier if the rival was of another ethnic group.


Now here we see men and women tending to rate sexual infidelity as more distressing, with race not seeming to have a major impact. Participants reported greater anger and hurt for sexual infidelity, which argues against the evolutionary explanations and argues for a role of self-esteem in how people respond.


Some feel that the gender differences are due to men and women making different assumptions, combined with a desire to keep what is theirs (Harris 1996). This social cognitive account says that the sex differences are due to differences in socially acquired beliefs, e.g. men and women believing that having sex either implied or did not imply being in love. This may explain some studies where men felt being sexually or emotionally involved would necessarily involve the other, but women were more likely to believe emotional attachment leading to sex rather than the other way round. Another study by Harris found that participants were more concerned about emotional infidelity than sexual infidelity, and that they felt that emotional infidelity implies sexual infidelity. The authors felt that men care more about sexual infidelity because it is probably not found without emotional infidelity, and that women are more concerned with emotional infidelity because they think men can have sex without being emotionally attached (Harris 1996b).


Visiting a brothel would be an interesting test of gender related jealousy. A study was done where people imagined a partner’s infidelity. Men tended to be less angry and hurt (opposite to evolutionary explanations). A male who is having an affair may find out that his lover is returning to her former partner. Evolution says that the partner would now have to raise someone else’s child and the original male does not, which would mean savings in terms of resources expended. Eighty-six people were given scenarios that highlighted just such a situation, but women reported more anger and hurt than males (Sabini 2005). Interestingly, males might show greater distress for sexual infidelity of their partners the longer they have been in a relationship (Buss 1992).


The study by Penke 2008 (see earlier) was taken by the author to be evidence against any evolutionary theory of jealousy, in that they did not find a significant male reaction to sexual infidelity, and while males were faster to respond to cues of sexual infidelity it was again not significant. They also felt that automatic processes were responsible for the gender pattern in emotional infidelity, which is different to the result in DeSteno 2002. They also varied the first presentation of type of infidelity presented first, and DeSteno always used the sexual condition first. He argued that environmental conditions were more likely to affect any underlying jealousy mechanism, although he did say that such influences could modify evolutionary mechanisms. DeSteno also found that in those German females with little education, this might indicate growing up in a deficit environment with relatively few stable relationships, resulting in greater female-to-female competition, in which case it would be adaptive for such women to show greater levels of jealousy (Penke 2008).


Another study that was performed to distinguish social and evolutionary theories put to participants a hypothetical situation about imagining the partner being unfaithful with a friend or a stranger. They found that there was no difference in the genders in terms of finding sexual infidelity more distressing. Participants were marginally more concerned when the other was a stranger. Also there was more concern with emotional infidelity the less the partners loved each other (Russell 2005). The conclusions were that neither theory was supported by the data, as the gender differential in jealousy responses was not seen and that there was no relationship between jealousy and sociological features, e.g. egalitarian features.


One interesting study looked at about 7700 finish twins with the aim of trying to figure out the relative important of various factors in jealousy. If only genetic factors caused differences between monozygotic and dizygotic twins, then the correlations of various measures in the MZ twins should be double that for the DZ twins. If shared environmental factors were responsible than the correlations should be about equal. If the MZ correlations are more than double that of the DZ twins then there may be non-additive genetic factors involved. They found that genes account for 30% of variation in jealousy, 28% due to non-additive genetic factors and about 70% from non-shared environmental factor. In a regression analyses jealousy was associated with restricted views on sex, desire and having been cheated on in the past or current relationships. The link between jealousy and desire was greater in women. There were also indications that in MZ twins, jealousy was higher in the one with restricted views on sex (Kupfer 2022).

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