social defeat

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PHYSIOLOGY&

BEHAVIORSEVIER Physiology & Behavior 73 (2001) 435-442

Social defeat as a stressor in humans

Kaj Bjorkqvist*

Abo Akademi University, PO. Box 311, FIN-65101 Vaasa. Finland

Received 2 November 2000; accepted 22 February 2001

act

Studies on social defeat in humans, and their similarities with studies on social defeat in animals are reviewed. Studies on social defeat in

ans typically are conducted as a branch of social psychology, most often focusing on bullying in schools and in workplaces. Victims ofying are known to suffer from depression, anxiety, sociophobia, loss of self-esteem, psychosomatic diseases, and other behavioralptoms. On the other hand, animal studies on social defeat, usually based on the rodent resident-intruder paradigm, present fmdingsed to physiological rather than to behavioral consequences of defeat. The two branches use different terminology, e.g., "dominant" andordinate" (animal studies) and "bully" and "victim" (human studies). It is suggested that the two fields could benefit from a mutualange in theory and methodology. ~ 2001 Elsevier Science Inc. All rights reserved.

ords: Social stress; Social defeat; Aggression; Bullying; Victimization; Dominant; Subordinate

ntroduction: lessons from animal models

The aim of the present article is to review studies on thect of social defeat in humans and to compare results

m these studies to findings obtained within research onal stress n subhuman species.

Research on social stress in animals, particularly inents, has developed a tradition with specific models,most popular being the resident-intruder paradigm (see,

Refs. [46,48]). In this model, a male rodent (theuder) is put into the home cage of another male (thedent). Alternatively, a cage with two compartments withmovable wall between them is used. As the wall isoved, the animals fight for a predetermined period ofe, almost inevitably leading to one of them taking a,ally severe, beating. The winner is often referred to asdominant male and the defeated animal as the subordi-male. The defeated animal is considered to experience

al stress.f they are allowed to fight on a single occasion only, it is

arded as a model of acute stress; if they are allowed tot at several consecutive occasions stretching over daysperhaps weeks, it is regarded as a model of chronic

stress. The subordinate may be exposed to chronic stressalso in the form of threat by, e.g., having to stay in thecompartment beside the dominant, exposed to its visual andodor cues, after having been defeated or between fights. Themodel works well as far as male rodents are concerned, buta problem with the model is that only male rodents may beused, since female rats and mice do not fight each other in aresident- intruder confrontation.

Animal studies suggest that social defeat may result in alarge variety of severe symptoms. They also suggest thatthese symptoms differ from those caused by other stressors.In fact, already a single experience of defeat inducesremarkable signs of stress in male rats: findings by Kool-haas et al. [45] indicate long-term (in this case, extendingover several weeks) effects, reminding of those of depres-sion in humans. Likewise, Blanchard et al. [20] found thatsubordinate male rats living in colonies together withaggressive males showed a number of symptoms typicalof depression. Indications of depression would hardly beseen n connection with plainly physiological stress, neitherin animals nor in humans. .

Corticosterone is known to playa role in mitigating theadverse effects of stress. Social defeat in male rodents byAlbeck et al. [3] was shown to cause an impaired cortico-sterone response, and they also found that the subordinatesexpressed a significantly lower number of corticotrophin-releasing factor mRNA grains per cell in the paraventricular

* Tel.: +358-6-3247-469; ax: +358-6-3274-491.E-mail address: [email protected] K. Bjorkqvist).



436 K. Bjiirkqvist / Physiology & Behavior 73 (2001) 435-442

intensity, the authors suggested hat the acute stress of defeatresults in a greater need of rest for the animal.

Kaplan and Manuck [43] studied the effect of socialdefeat in male macaques and in socially stressed, sociallyhoused female ovariectomized macaques [41]. In both cases,they found an enhanced disposition for coronary athero-sclerosis in subordinated animals, males and females alike-although fertile nonovariectomized female macaques,

like women, are resistant to atherosclerosis. They concludedthat circulating estrogen is likely to prevent atherosclerosisin nonovariectomized females.

Stress caused by social defeat may also be related to drugabuse. Tidey and Mizcek [89] found that when given theopportunity to administer cocaine to themselves, defeatedmale rats acquired self administration habits in half the timeofnondefeated males. They also examined, by use ofin vivomicrodialysis, dopamine concentrations in nucleus accum-bens. Extracellular dopamine levels in nucleus accumbensincreased o 135% of baseline in defeated rats as compared to125% of baseline in nondefeated rats. Furthermore, whenexposed to social threat by the resident, the levels changed to145% in defeated rats vs. 120% in nondefeated rats. Theauthors suggested that exposure to stress may inducechanges in central dopaminergic activity, rendering theindividual more vulnerable to self-stimulation due to across-sensitization to the rewarding effects of cocaine.

In their review of studies based on mice, Laviola et al.[51] suggest that adolescence, n both animals and humans,may be associated with an increased risk of drug abuse. Thismay be due to the fact that novelty-seeking behavior istypical of this period, but there may also be an underlying,

strictly biological, explanation: in animal models of prea-dolescence, the search for novel stimuli and sensationsshares a common neurological substrate with psychostimu-lants, the reward-related mesolimbic pathways.

As previously pointed out, animal models of social defeat,and in particular, those based on rodents, almost exclusivelyuse males as subjects. This weakness has troubled research-ers, and Railer et al. [37] underlined that reliable social stressmodels for females are virtually lacking. They suggested hatsocial instability might be a useful alternative as a socialstress ndicator in female rodents: in order to create a sociallyunstable environment for female rats, they alternated phasesof isolation with mixed-sex crowding, including rotatingmembership during the crowding phases. The effect of socialstress, nduced in this manner in females, was compared tothe effect of the social defeat paradigm in males. Defeatstress reduced weight gain and increased both adrenals andplasma corticosterone in males, while social stress had aneffect only on adrenal weight in females. The questionremains, however, to what extent the social stressors n thesetwo cases really are comparable.

Conclusively, the animal social defeat model hasrevealed a number of quite severe consequences of social

defeat in animals of various species. The examples providedabove are by no means intended as a comprehensive over-

hypothalamic nucleus as compared to dominants and cage-housed controls.

Sgoifo et al. [83] found that social stress, in contrast toother stress contexts, produced a shift of autonomic balancetoward sympathetic dominance, associated with the occur-rence of cardiac tachyarrythmias, in male rats, especially inthose of a wild strain.

Social defeat results in clear changes in hormonal and

neurotransmitter responses in rats: for instance, Stefanski[85] investigated the specific hormonal response patterns ofwinners and losers after a 7-day period of chronic confron-tation. At Day 7, winner males showed stable concentrationsof corticosteroid-binding globulin (CBG) and reduced titersof total corticosterone, while losers had a marked decreasein CBG and unaffected total corticosterone. Increased nor-epinephrine and epinephrine titers were also evident inlosers. Furthermore, reduced testosterone levels wereobserved in the defeated males.

Similar effects have been found in pigs. Otten et al. [69]found socially defeated pigs (in contrast to the rodentstudies, the sample consisted in this case of females andcastrated males) to show an increase in plasma catechol-amines, ACTH, and heart rate. Immediately after the intro-duction of an intruder, loser pigs responded with asignificantly higher increase in plasma epinephrine andnorepinephrine concentrations than did winner pigs. Losersalso showed reduced locomotor activity and exploringbehavior, i.e., they showed not only physiological but alsobehavioral symptoms, suggesting more emotional distressand fear as compared to winning pigs.

Levels of nerve growth factor (NGF), a polypeptide

growth factor exerting trophic and differentiative effectson both peripheral and CNS neurons, have been shown toincrease subsequent o aggressive encounters n mice [4-6].They suggested that when released into the bloodstreamafter psychosocial stress, NGF affects peripheral nervousstructures (chromaffm cells and ganglia) and peritoneal mastcells [4]. Others [1,87] have made similar fmdings.

There are also clear indications of impaired immunolog-ical function as a result of social defeat. For instance,Stefanski and Engler [86] studied the effects on winningand losing among male Long- Evans rats on Days 2 and 7 ina chronic social stress design. On both Days 2 and 7, losersshowed reductions in the number of blood CD4 and CD8Tcells, and they also showed a suppression of in vitrolymphocyte proliferation. Winners, on the other hand,showed similar immunological changes only on Day 2 ofconfrontation. Cohen et al. [25] found impaired immuno-logical function and increased susceptibility to respiratoryinfection in socially defeated male macaques. Weiss andSundar [91] and Biondi et al. [II], in their reviews of theeffects of stress on cellular immune response in animals,report similar findings in other species.

A single experience of social defeat has been shown to

increase slow-wave sleep in rats as measured by EEG [59].Since slow-wave activity is thought to be a sign of sleep



K. Bjiirkqvist / Physiology & Behavior 73 (2001) 435-442

view, but they show evidence of at least the followingeffects of social defeat in animals: impaired corticosteroneresponse in male rats [3,85], decrease n testosterone evelsin male rats (e.g., Ref. [85]), increase n plasma epinephrineand norepinephrine in male rats [85] and in female andsterilized male pigs [69], increase n plasma catecholamines,ACTH, and heart rate in female and castrated male pigs[69], a general shift of autonomic balance toward sympa-

thetic dominance, associated with the occurrence of cardiactachyarrythmias in male rats [83], enhanced disposition foratherosclerosis in both male and ovariectomized femalemacaques [43,44], increased NGF expression in male mice[4-6], impaired immunological function in male rats[85,86], male macaques [25], and in a number of otherspecies as well [8,91], increase in slow-wave sleep in malerats [59], increased self-administration of cocaine andchanges n dopaminergic activity, which may cross-sensitizeto cocaine self-administration, in male rats [89], reducedweight gain in both male and female rats [37], and decreasedlocomotion and exploring behavior in female and castratedmale pigs [69].

Now turning our focus toward research on social defeatin humans, the first observation made is the relative absenceof laboratory experiments. Experiments in which humansexperience severe social defeat will hardly be approved bythe ethics board of any present-day university. Accordingly,the main part of these studies is correlational, and accord-ingly, they usually lack the baseline measurements possiblein laboratory designs. However, a few experiments on socialdefeat in humans have been conducted.

2. Dominance, defeat, and testosterone

A popular research topic in the area has been theinvestigation of whether defeat is related to reduced testos-terone levels based on the rationale that testosterone, dom-inance, and aggression ~ay be related not only in subhumanspecies but also in humans.

Rejeski et al. [77] examined cardiovascular and testos-terone responses in dominant and submissive male under-graduates, who engaged in a debate with a trained female.While dominant males reported a subjective greater loss ofdominant status as a result of the debate, the submissiyemales manifested greater decrease in testosterone levels.Heart rate data revealed that, as the debate continued, thedominant males habituated to the situation, while the sub-missives experienced increased threat.

In another study, Rejeski et al. [78] studied cardiovas-cular and testosterone responses in dominant and sub-missive female undergraduates in a similar design.Dominant females reacted more to the social stress withcardiovascular parameters than submissive ones. However,

serum testosterone did not vary as a function of theexperimental manipulation.

Jeffcoat et al. [42] investigated whether endocrinechanges could be induced in five men confined on a boatfor 14 days. The participants were secretly ranked fordominant/aggressive behavior toward the other men. Asignificant correlation was found between day-to-daychanges in self-assessed anxiety and stress hormones, corti-sol, and prolactin. A significant correlation was found alsobetween plasma prolactin, testosterone, and rank position

for dominance/aggression. The authors concluded that underat least some circumstances, social interaction might modifyendocrine status in human males.

One of the earliest studies on the relationship betweentestosterone, aggression, and dominance among humanmales was conducted by Ehrenkranz et al. [31 , with maleprisoners as participants. They found a significant relation-ship between testosterone and both aggression and dom-inance. Dabbs et al. [29] found higher levels oftestosterone among prisoners convicted for violent crimesthan among prisoners convicted for nonviolent crimes.Kreuz and Rose [47] made a similar study but failed tofind any such relationship. However, they found higherlevels of testosterone than among others among a smallsubgroup of 10 inmates who had committed violent crimeduring their adolescence.

A link between high testosterone and violence was foundby Rada et al. [74] among a small group (n = 5) of sexual

offenders (rapists and molesters) udged by police records tobe more violent than other offenders. Another study ofoffenders by Olweus et al. [67] provided mixed results.Bain et al. [9] did not fmd any difference in testosteronelevel between three groups of offenders convicted either for

property offence, assault, or repeated assault.Accordingly, there are studies suggesting a link between

testosterone and aggression in human males convicted forsexual offense or violent crime, but the findings are equiv-ocal. However, since these studies concern samples ofprison inmates, generalizations to the population-at-largemust be made with caution.

Dabbs [26] conducted a similar study with female prisoninmates as participants. Testosterone was measured fromradioimmunoassay of saliva samples. He concluded that,like in male prisoners, testosterone ndeed was also linked toaggressive dominance in female inmates.

Cashdan [24] investigated hormonal correlates of domi-nance and status in coresidential college women. She foundthat estradiol, total testosterone, and free testosterone allwere related to high self-regard, number of sexual partners,and infrequent smiling, a behavior usually associated withdominance. Dabbs [28], for instance, found that low-t~stos-terone men were smiling more frequently and with broadersmiles than did high-testosterone men.

Although there may be a link between social dominanceand testosterone in small-group interaction among bothmales and females, there is no evidence of any correlation

between testosterone and social/occupational status. Theopposite may in fact be the case: Dabbs [27], who inves-



438 K. Bjorkqvist I Physiology & Behavior 73 (2001) 435-442

testosterone being linked to high status. Instead, the oppo-site appears to be the case [27].

Summing up, when groups of males (and surprisingly, alsofemales) spend much time together and interact intensivelywith each other, like in prison, on a boat, or in a coresidentialcollege -perhaps also in the army, in school, or at theworkplace -social defeat appears to reduce testosteronefrom baseline levels. On the other hand, individuals low intestosterone may also appear less threatening to their peers,and, accordingly, they may become socially defeated moreeasily. Thus, the testosterone-dominance relation brings tomind the old question of which is hen and which is egg:clearly, testosterone and dominance seem o interact with eachother, and a circular effect may also occur.

3. Bullying in schools

tigated 4462 foffiler US military servicemen, found thatparticipants with higher levels of serum testosterone hadlower-status occupations. As an explanation, Dabbs sug-gested that since serum testosterone is thought to beheritable and available at an early developmental stage,high levels presumably evolved in association with domi-nance in individual and small-group settings. Thus, testos-terone, which perhaps evolved in order to support a

primitive kind of status, in fact, in today's society, isassociated with low socioeconomic status.

Schaal et al. [82] and Tremblay et al. [90] conducted alongitudinal study of boys from 6 to 13 years of age,following their development with regards to testosterone,dominance, and aggression. At age 13, social dominanceand testosterone evels were assessed during a I-day visit tothe laboratory, together with four unfamiliar peers. Boysperceived by the peers as dominant had higher levels oftestosterone than others. However, a positive correlationbetween testosterone and aggressiveness was not found: infact, boys who had a history of high physical aggression hadlower levels of testosterone than boys with no such history.

Bjorkqvist et al. [16] administered testosterone, placebo,or no drug to adult human males. They did not observe anyincrease n aggression n the testosterone group; however, theplacebo group (!) showed and increase n aggression, both incomparison with the controls and the testosterone group.

Mazur and Lamb [58] found increased evels oftestoster-one among winners in a tennis competition but not amongwinners in a ottery. Also, new recipients of an MD degree hadincreased testosterone. They concluded that when a rise instatus s achieved, testosterone evels increase.

Conclusively, there appears to be support for the notionthat testosterone s linked to dominance in humans, althoughmainly in small-group settings; the findings are so farinconclusive with regards to social/occupational status.The link to aggressiveness s less clear, demonstrated insome studies (e.g., Refs. [31,67)), but not in others (e.g.,Refs. [16,82,90)). In his review, Archer [8] suggests thatthere is reasonable evidel;lce for a link between aggressive-ness and testosterone among adult human males but notamong adolescents. As Benton [10] points out, the claim ofa relationship between testosterone and aggression is unam-biguously demonstrated only in animal data. Human aggres-sion is often instrumental and calculated rather thanemotogenic, i.e., related to anger. As far as human aggres-sion is concerned, social and cognitive factors playa muchgreater role than physiological factors. The higher up on thephylogenetic scale, the more uncertain the relationshipbetween aggression and testosterone appears to be.

Testosterone-related dominance in small groups may beobserved in nonverbal and verbal communication, such asless smiling and more frequent interruption of others[24,26,28]. With regards to small-group interaction, thereappears to exist a testosterone-dominance link similar to

that found in subhuman species. However, with respect tosocial/occupational status, there is no evidence at all of

There exists a large body of research on social defeat inhumans, which has been totally neglected by social stressresearchers. This is the research on bullying in schools andwork places.

Bullying was defined by Sullivan [88] as a conscious andwillful act of aggression and/or manipulation by one or morepeople against another person or people. Bullying can last fora short period or go on for years and is an abuse of power bythose who carry it out. Others (e.g., Refs. [13,15,63-65])explicitly stress that it is an unequal-power relationshipbetween aggressor (the bully) and victim, and the victim is,for some reason or another, not able to defend him/herself. It is

usually an ongoing process, with the bullying increasing inseverity. However, also, single acts may be regarded asbullying when characterized by abuse of power.

Often, bullying does not appear to have any other mean-ingful purpose than to humiliate the victim, thereby increasingthe bully's self-esteem and scaring others ("look what mayhappen to you if you oppose me"). In a school class withbullying problems, there typically is one main bully with afew armor-bearers or supporters and one or two victims, androughly 60- 70% of the pupils are silent onlookers or bystand-ers [14,63,65,81]. However, as the bullying increases inseverity, more and more pupils typically take part, turning itinto a process of group aggression [49].

Typically, besides being beaten up, the victim often ispressured to bring money to the bully or to do otherservices. He is also threatened with revenge in case heattempts to get help from teachers or other adults. Suicidescaused by school bullying have been reported in severalcountries [60,66].

At fIrst, the research focus was on physical bullying[63,65]; however, soon it was discovered that much of thebullying occurring in schools was in fact of psychologicalnature, conducted as indirect aggression, manipulating the

social fabric of the class in order to exclude the victim fromthe social groups of the class, and having him/her rejected



K. Bjiirkqvist / Physiology & Behavior 73 (2001) 435-442 439

by peers. This type of bullying was found to be particularlyprominent among girls [10,19,50,68,92].

Research on bullying in schools commenced in the 1970s[56,63,65]. Most of the early studies were conducted inScandinavia [12,17,49,63-66,80,81]; later on, research wastaken up in the UK, Australia, and New Zealand[22,70,79,84,88,92]. The phenomenon is well known alsoin Japanese schools, where it is called ijime [60]. Research

on bullying in the USA has been scarce, but some studies doexist; (for a review, see Harachi et al. [39]). Slightly moreresearch n the area has been conducted in Canada [38,73].However, there is a related body of research n US focusingon peer rejection [21,71,72]. Partly, it appears to be aquestion of terminology.

At present date, research on school bullying is going onin a large variety of countries on all continents, indicatingthat the phenomenon is not limited to any specific culture,but it appears o be universally human [62,84].

Bullying has interesting parallels with animal models ofsocial defeat, the bully being equivalent to the dominantanimal and the victim to the subordinate one. A singleincident of bullying may be compared to the acute stressmodel and ongoing bullying to the chronic stress model.

There can be no doubt about the fact that victims ofschool bullying experience severe stress due to social defeat.What is known about the consequences of bullying?Bjorkqvist et al. [14] found victims to be depressed, havepoor self-esteem, feel themselves as failures, and feelthemselves (wrongly) to be unintelligent, poor academicachievers, and ugly. Lagerspetz et al. [49] found victimslikewise to have low self-esteem, having a subjective feeling

of maladjustment, and showing grave dissatisfaction withschool and peer relations. Olweus [63,65] found high levelsof anxiety in victims. Hawker and Boulton [40], in theirreview of others' studies, conclude that victims typicallyshow the following characteristics: loneliness, depression,anxiety, low self-esteem, submissiveness, social withdrawal,and unpopularity among peers. These symptoms occuramong male and femal~ victims alike.

Accordingly, chronic stress in the form of social defeat-victimization to bullying -has severe behavioral con-sequences. A problem, of course, is that since the researchusually (ifnot always) is post hoc, no baseline (prebullying)measures of symptoms exist. Furthermore, so far, there arefew, if any, studies using physiological measures, like inresearch based on animal models.

Gustavsson [55] as the pioneers. Again, research in the areabegan in Scandinavia [7,13,18,19,32,33,52-55], from whereit spread to the Gennan-speaking areas of Europe [34,61]and to the UK [2,76].

Research on workplace bullying took school bullying asits starting point and source of inspiration, defining bullyingin the same way. Bjorkqvist [13] described three distinctstages of workplace bullying: (1) Stage 1 is characterized byindirect aggression, such as gossiping and backbiting; (2)Stage 2 is characterized by open verbal confrontations,followed by social rejection of the victim, who typically isnot spoken to or looked at; (3) during Stage 3, the bullytries, and often succeeds, in forcing the victim out of theworkplace, losing his/her employment.

Although workplace bullying reminds of school bullying,there are also important differences. At workplaces, thecompetition about jobs is an important intervening factor,and bullying often occurs between employees of similar orclose occupational status, competing for the same position.

Both women and men are victimized by workplace bullying,and unlike school bullying, which mostly takes place betweenmembers of the same sex, workplace bullying occurs almostas frequently between members of different sexes as betweenemployees of the same sex. The competition about position isa factor more important than gender [13,18].

The social group formed by colleagues at work is,besides the family, probably the most important referencegroup for the adult individual. Each person's self-image isdependent on how (s)he is treated by colleagues. Further-more, losing one's job may imply losing much more -economy, career, and future. No wonder that exposure to

workplace bullying has been shown to have quite severeconsequences, and suicides are not uncommon [52,53].Leymann [52] provides evidence that victims of workplacebullying frequently show symptoms typical of posttraumaticstress disorder. If an employee is exposed to bullying bycolleagues, especially by the boss, not being able to defendhim/herself, the mean length of time for serious symptomsto appear is as short as 15 months [52].

Other typical consequences reported are depression,sociophobia, anxiety, loss of self-esteem, psychosomaticdisorders, and sleep disorders. All these symptoms havebeen demonstrated among males as well as females[7,13,18,32,33,52,53].

5. Social defeat in females

4. Bullying in work places As indicated above, human females are not unaggr~ssive.During the last decades, emale aggression has been studiedextensively, especially the female propensity for indirectaggression [12,15,19,50,68]. In her review, Hyde [41] con-cluded that when aggressive, females try to cause psycho-logical rather than physical harm to their enemies, and Eagly

and Steffen [30] and Frodi et al. [35], in their reviews, cameto similar conclusions. Although less physically aggressive

The f1fSt study of workplace bullying -sometimes alsocalled work harassment (not to be confused with sexualharassment at workplaces, a sexist variety) -was conductedby Brodsky [23] in 1976. His study was ahead of time, and

research on workplace bullying did not gain momentum untilthe late 1980s, with Leymann [52-54] and Leymann and



440 K. Bjiirkqvist / Physiology & Behavior 73 (2001) 435--442

describe "bullies" and "victims." With the wrong keywords, a search in psychological abstracts may be futile.

Animal and human studies on social defeat should beable to benefit from each other by a mutual understandingof and communication about both theory and methodology.As an example, a worthwhile pursuit would be to inves-tigate whether findings related to social defeat in animalsmay be replicated with humans, in research on defeat insports, and in studies on bullying and victimization inschools and workplaces.

References

than males, the human female has found other ways toaggress against her enemies. In fact, laboratory studies showthat when not in danger of being recognized, hence of beingretaliated against, females behave equally aggressively asmales [36,57,75].

Human females, accordingly, are victimized to aggres-sion by other females. They are also victimized to aggres-sion by males. As research on bullying in schools andworkplaces has shown, human females frequently experi-ence severe stress in the form of social defeat, with similarsymptoms as seen in males.

However, we also do know that females in some respectsreact differently to social stress than males: for instance,human males may develop coronary atherosclerosis, a dis-ease hat nonovariectomized females before the menopauseare protected against [43,44]. Hence, there is a need forfemale social stress models in animals.

As mentioned in the introduction, the rodent resident-intruder paradigm is not possible to use with female rats and

mice as subjects, since they do not aggress against each otherin that particular situation. Accordingly, alternative animalmodels of female social stress need o be discovered. Hailer etal. [37] suggested hat an unstable social situation might beone possibility. However, this source of stress appears lessdramatic than for instance bullying among humans, andcertainly, it does not represent social defeat. Perhaps miceand rats are not very well suited for the purpose, and otheranimals, in which females are known to show visible aggres-sion- such as the golden hamster, he pig, and the hyena -would be better suited for the purpose.

6. Final comments

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[2] Adams A. Bullying at work: how to confront and overcome it. Lon-don: Virago, 1992.

[3] Albeck DS, McKittric CR, Blanchard CD, Blanchard RJ, Nikulina J,

McEwen BS, Sakai RR. Chronic social stress alters levels of cortico-trophin-releasing factor and arginine vasopressin rnRNA in rat brain.J Neurosci 1997;17:4895-903.

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[9] Bain J, Langevin R, Dickey R, Ben-Aron M. Sex honnones in mur-derers and assaulters. Behav Sci Law 1987;5:95-101.

[10] Benton D. .Honnones and human aggression. In: Bjorkqvist K, Nie-melii P, editors. Of mice and women: aspects of female aggression.San Diego, CA: Academic Press, 1992. pp. 37-48.

[II] Biondi M, Massimo Z, Luca G. Psychological stress, neuroimmuno-modulation, and susceptibility to infectious diseases in animals andman: a review. Psychother Psycllosom 1997;66:3-26.

[12] Bjorkqvist K. Sex differences in physical, verbal, and indirect aggres-sion: a review of recent research. Sex Roles 1994;30:177-88.

[13] Bjorkqvist K. Trakassering forekommer bland anstiillda vid AA. MedAA 1992;9:14-7.

[14] Bjorkqvist K, Ekrnan K, Lagerspetz KMJ. Bullies and victims: theirego picture, ideal ego picture and nonnative ego picture. Scand J

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and boys fight? Developmental trends in regard to direct and indirectaggression. Aggressive Behav 1992;18:117-27.

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D, Olweus D, Catalano R, Slee P, editors. The nature of school bullying:a crQss-national perspective. London: Routledge, 1999. pp. 56-67.

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[19] Bjorkqvist K, Ostennan K, Lagerspetz KMJ. Sex differences in covertaggression among adults. Aggressive Behav 1994;20:27-33.

The present article was written with the specific purposeof attempting to find common ground between studies onsocial defeat in humans and in animals. Since I am con-ducting research with human subjects, my comments andreflections about subhuman species run the obvious risk ofappearing naive and simplistic. However, this is a risk thathas to be taken in order to enhance communication betweenthe two fields.

Research on social defeat in animals is usually conductedby biologists or physiological psychologists, within thebroader framework of social stress studies, often with thepurpose of using the model for the testing ofpsychopharma-cological agents against anxiety and depression. Research onsocial defeat in humans, on the other hand, has developed asa branch of social psychology, with little awareness, f any atall, of the studies made with subhuman species as subjects,despite the fact that these should be of great relevance for theunderstanding of the consequences of victimization.

Accordingly, one obvious problem in the communicationbetween human and animal studies on social defeat is that of

terminology. For example, the animal literature uses termslike "dominant" and "subordinate," while human studies



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