Testosterone causes both prosocial and antisocial status-enhancing behaviors in human males

14 Pages·2016·1.08 MB·English

Testosterone causes both prosocial and antisocial
status-enhancing behaviors in human males
Jean-ClaudeDrehera,b,c,1,2,SimonDunnea,d,1,2,AgnieszkaPazderskae,ThomasFrodla,f,g,JohnJ.Nolane,h,
andJohnP.O’Dohertya,d,i
aTrinityCollegeInstituteofNeuroscience,TrinityCollegeDublin,Dublin2,Ireland;bNeuroeconomics,RewardandDecisionMakingLaboratory,Institutdes
SciencesCognitivesMarcJeannerod,CNRS,69675Bron,France;cDépartementdeBiologieHumaine,UniversitéLyon1,69622Villeurbanne,France;
dComputationandNeuralSystems,CaliforniaInstituteofTechnology,Pasadena,CA91125;eDepartmentofEndocrinology,St.James’sHospital,Dublin8,
Ireland;fDepartmentofPsychiatryandPsychotherapy,OttovonGuerickeUniversityofMagdeburg,39106Magdeburg,Germany;gDepartmentof
Psychiatry,SchoolofMedicine,TrinityCollegeDublin,Dublin2,Ireland;hStenoDiabetesCenter,2820Gentofte,Denmark;andiDivisionoftheHumanities
andSocialSciences,CaliforniaInstituteofTechnology,Pasadena,CA91125
EditedbyBruceS.McEwen,TheRockefellerUniversity,NewYork,NY,andapprovedAugust16,2016(receivedforreviewMay23,2016)
Although popular discussion of testosterone’s influence on males functionofmaintainingsocialdominanceandestablishingaccess
oftencentersonaggressionandantisocialbehavior,contemporary to mating opportunities (13). This proposition originates from
theoristshaveproposedthatitinsteadenhancesbehaviorsinvolved the literature on the role of testosterone in birds and primates
inobtainingandmaintainingahighsocialstatus.Twocentraldis- (14). It is supported by evidence of an association between tes-
tinguishingbutuntestedpredictionsofthistheoryarethattestos- tosteronelevelsandsocialrankinnonhumanprimates(15)and
terone selectively increases status-relevant aggressive behaviors, observations that administration of testosterone to lambs and
suchasresponsestoprovocation,butthatitalsopromotesnonag- tropical birds selectively increases aggressive dominance behav-
gressive behaviors, such as generosity toward others, when they iorswhenthe statushierarchyisunstable (16,17).
areappropriateforincreasingstatus.Here,wetestedthesehypoth- Although increased aggression may be critical inachieving so-
esesinhealthyyoungmalesbyinjectingtestosteroneenanthateor cial rank among other animal species, human social interactions
aplaceboinadouble-blind,between-subjects,randomizeddesign are arguably more complex, and status may be obtained by non-
(n=40).ParticipantsplayedaversionoftheUltimatumGamethat aggressive, even prosocial, means, such as generosity (18–20).
wasmodifiedsothat,havingacceptedorrejectedanofferfromthe Although human generosity often occurs without an expectation
proposer,participantsthenhadtheopportunitytopunishorreward of material benefit (21), experimental research has shown that
theproposerataproportionatecosttothemselves.Wefoundthat generositytootherscanalsohaveasocialsignalingfunction;for
participants treatedwith testosteronewere more likely to punish example,itisincreasedwhendonationswillbemadepublic(22–
theproposerand thathigher testosterone levelswere specifically 24),andmalegenerosityspecificallyisincreasedinthepresenceof
associatedwithincreasedpunishmentofproposerswhomadeun- femaleobservers(25).Thisgenerosityhasbeenrepeatedlyshown
fairoffers,indicatingthattestosteroneindeedpotentiatesaggres- toincreaseratingsofthegiver’ssocialstatus(19,22,26),leading
sive responses to provocation. Furthermore, when participants togreaterinfluenceingroupdecisionmaking(26)andelectionto
administered testosteronereceivedlargeoffers,theyweremore leadershippositions(27)aswellasreciprocalgenerosity(22,27).
likelyto rewardthe proposer andalso chose rewards of greater In line with this observation, an alternative theory of testos-
magnitude. This increased generosityin the absenceof provoca- terone’s effect on male behavior proposes that, instead of pro-
tionindicatesthattestosteronecanalsocauseprosocialbehaviors motingonlyaggressivebehaviors,testosteronepromotesbehaviors
that are appropriate for increasing status. These findings are in- intendedtoachieveandmaintainsocialstatusordominance(28,29).
consistent with a simple relationship between testosterone and This theory predicts that, while in social contexts where status is
aggression andprovidecausalevidencefora morecomplexrole
fortestosteroneindrivingstatus-enhancingbehaviorsinmales.
Significance
| | | |
testosterone aggression generosity humanmales socialstatus
Althoughinseveralspeciesofbirdandanimal, testosteronein-
DS
The gonadal steroid hormone testosterone has long been creasesmale–maleaggression,inhumanmales,ithasbeensug- ANNCE
mcppirosaoerivaknlyerntyneodnmwemantaneoicrntremoestiorpncefhliaanapmyglhleayvinstiisfegcuwiannblsgde.mhaasmaEasvoseaicocnruilrtaylaaitllneairneziotafimfltepeioacriitlnnnscr(teii1hpns,eaelah2ldry)uce.mwhvHeaitalnohonwpdamemgvacgeelorneren,ststspeahirmonaends-- gbdtahieedseshtostianeeuvdgbhioulyetripos-sbholtiitinnhnhgsadett,setehraeasednnsihndepaormanomccemceionzoeusitodnnecjtdeisabeciltosseitsgldhtanacwt.akuPgiinstagh.grrtH.eticeHsoisspewtivaroeeens,vttweesarrnpeo,dlnactaeyenuseootdsenradaalpglmbeagvecoriteeddwbseifsoeniieevcindnee PSYCHOLOGICALCOGNITIVESCIE
Ultimatum Game, which included the opportunity to punish or
andantisocialbehavior(3–5).Inhumans,oneinfluentiallineof
reward the other player. Administration of testosterone caused
supportingevidenceforthisassociationcomesfromstudiesthat
increasedpunishmentoftheotherplayerbutalso,increasedre-
showed that male prisoners with high testosterone levels are
wardoflargeroffers.Thesefindingsshowthattestosteronecan
morelikelytohavecommittedviolentcrimesandbrokenprison
causeprosocialbehaviorinmalesandprovidecausalevidencefor
rules than those with low testosterone levels (6–8). The limited
thesocialstatushypothesisinmen.
number of experimental studies that have manipulated male
testosterone levels during economic games (9, 10) found that
Authorcontributions:J.-C.D.andJ.P.O.designedresearch;J.-C.D.,S.D.,A.P.,T.F.,andJ.J.N.
administration of testosterone caused participants to be less performedresearch;S.D.analyzeddata;andJ.-C.D.andS.D.wrotethepaper.
generous to others (10) and more likely to punish those who Theauthorsdeclarenoconflictofinterest.
stolefromthem(9).Thesestudieshave,however,beencriticized
ThisarticleisaPNASDirectSubmission.
formethodologicalproblems(11),andthecausalevidenceforan
1J.-C.D.andS.D.contributedequallytothiswork.
associationbetweentestosteroneandaggressioninhumanmales
2Towhomcorrespondencemaybeaddressed.Email:[email protected]
remainsweak(12).
[email protected].
Inhumans,ithasbeensuggestedthatendogenousincreasesin
Thisarticlecontainssupportinginformationonlineatwww.pnas.org/lookup/suppl/doi:10.
testosteronefacilitateaggressionincompetitivecontextswiththe 1073/pnas.1608085113/-/DCSupplemental.
www.pnas.org/cgi/doi/10.1073/pnas.1608085113 PNAS | October11,2016 | vol.113 | no.41 | 11633–11638
Fig. 1. Illustration of trial. Participants accepted or
rejectedanoffertosplitasumofV12.Participants
thenchosetopunishorrewardtheproposeratacost
tothemselves ordo nothing.Afteraninterstimulus
interval(ISI),theyspecifiedthemagnitudeofpunish-
mentorreward.Finally,participantssawthenettrial
winningsofbothplayersandanintertrialinterval(ITI).
threatenedbyperceivedprovocation,thismotivationmayindeed status-enhancing behaviors, we would expect to see no increase
lead to increased aggression; in others, nonaggressive behaviors, inrewardofgenerousoffers.
suchasgenerosity,willbemoreappropriateforadvancingsocial Concernhasbeenraised(33)thatostensiblyemotionalbehav-
statusandwill,therefore,bepromotedbytestosterone. iors in economic games among participants administered testos-
There is some evidence that, rather than giving rise to in- teronemay,infact,bedrivenbyrationalconcerns.Iftestosterone
discriminate aggression, testosterone may indeed be associated administration influences participants’ beliefs about the likely
with aggressive responses to perceived provocation, so-called re- strategyoftheiropponents,anydifferenceinbehaviorassociated
activeaggression,asthestatustheorypredicts(30).Anumberof with such a manipulation may simply be a strategic earnings-
findingsalsolinkstestosteronewithnonaggressivestatusseeking. maximizing response to these changed beliefs. Uniquely, our de-
Theworkinref.31foundthatthetestosteronelevelsofdominant signexcludesthisinterpretation,becauseparticipantswereaware
but nonviolent males were indistinguishable from those of their thattheproposers’behaviorhadbeenrecordedbeforehand,and
violentpeersandthatthetestosteronelevelsofbothgroupswere therefore, the proposers had no opportunity to respond to the
significantly higher than those of their nondominant peers, and participants’ own behavior. Thus, although participants believed
the work in ref. 29 found that making a task relevant to status thattheirchoicestoreject,punish,andrewardhadrealfinancial
increased performance in a test of mathematical ability in high- consequencesfor theproposers, participants couldnotuse these
testosteronemalesspecifically.However,withoutadirectexperi- behaviors as instruments to influence the proposers’ offers, and
mentalmanipulationoftestosterone,itisnotpossibletoruleout they did not need to anticipatethe proposers’ responses to their
the possibility that another variable correlated with testosterone behavior.Infact,aplayerwhowishedtomaximizehisearningson
ourtaskshouldsimplyacceptalloffersandneverchoosetopunish
maybedrivingthesenonaggressivebehaviors.
orrewardtheotherplayer.
The correlational nature of the supporting literature means
that the distinguishing predictions of the status theory of tes-
Results
tosterone for male behavior remain untested. First, it has not
Effects of Treatment on UG Behavior. After confirming that our
been shown that, rather than promoting indiscriminate aggres-
administrationoftestosteronewassuccessfulinproducingaclear
sion, testosterone selectively causes male reactive aggression in
circumstances in which an individual’s status is threatened. Sec- increase in the serum testosterone levels of the treatment group
relativetotheplacebogroup(SIResultsandFig.S1),weanalyzed
ond, it has not been shown that testosterone may cause non-
participants’choicestoacceptorrejectproposers’offerstodivide
aggressive, even prosocial, behaviors in males if those behaviors
the endowment (Fig. S2 and Table S1). We found a significant
areconsistentwithincreasingstatus.
positive effect of the amount offered to the participant on the
Toaddressthesequestions,weinjectedtestosteroneorplacebo
probability of acceptance (β=0.93, SE=0.07, P<0.001) but no
in a double-blind, randomized procedure to a group of young
effect of treatment group or the interaction of treatment group
maleswhothenplayedamodifiedversionoftheUltimatumGame
andamountoffered.
(UG).TheclassicUGisaneconomicgameinwhichtwoplayers
On the subsequent choice, at which participants decided
mustdecidehowtosplitasumofmoneybetweenthem.Ineach
whethertopunish,donothingto,orrewardtheproposer(Fig.1
round, the first player, the proposer, presents a proposal to the
andTableS2),weagainfoundasignificantpositiveeffectofthe
second player, the responder, which describes how this money
amount offered as well as a significant positive effect of the in-
should be divided. The responder may accept this proposal, in
teraction of treatment group and offer amount. The results of
whichcasethesplitisimplemented,orrejectit,resultinginboth
this ordered probit regression indicate that participants admin-
playerswinningnothing.Ourparticipantsplayedtheroleofthe
istered testosterone were more likely to punish proposers who
responderinaUGthatwasmodifiedsothat,havingacceptedor
offered below-average amounts, whereas for offers of above-
rejectedaproposedsplit,theyhadtheoptiontorewardorpunish
averageamounts,theyweremorelikelytorewardtheproposer.
theproposerbyincreasingordecreasingtheirmonetarypayoffata Wecarriedoutadditionalanalysestodeterminewhetherthese
proportionalcosttothemselves. effectsoftreatmentwereattributabletoadifferencebetweenthe
According to testosterone’s proposed role in driving status- groupsintheirpropensitytopunishonlyoradifferenceintheir
enhancing behaviors, the predicted effect of testosterone ad- propensity to reward only. We performed two binary probit re-
ministrationonparticipants’choiceswoulddependonthesocial gressions of their choices on treatment group, amount offered,
context.Offersofsmallamountsofmoneywouldbeperceivedas and their interaction: the first regression coding choices to
unfair(32)andbepunishedmorestronglybythoseadministered punishasone andchoicesto donothing or punishaszero,and
testosterone, but reward of generous offers would not be de- the second coding choices to reward as one and choices to do
creasedbytreatment.Incontrast,iftestosteronesimplyincreases nothing or reward as zero (Table S2). Null effects of treatment
indiscriminate aggression, we would expect to see both greater group in one or both of these analyses would indicate that tes-
punishment of unfair offers and reduced reward of generous tosterone administration did not influence rates of both pun-
offers. Additionally, the status theory of testosterone predicts ishmentandreward.Inbothcases,however,weobservedeffects
thatoffersoflargeamountsofmoney wouldbeexpectedtofa- oftreatmentgroup.Wefoundapositivemaineffectoftreatment
cilitate status-enhancing displays of generosity and therefore, group (β=0.07, SE=0.32, P=0.03) as well as a positive in-
that, when men injected with testosterone were offered large teraction of treatment group with offer amount on punishment
amounts, they would reward the proposer more than those ad- rate ðβ=0.18, SE=0.04, P<0.001). Follow-up analyses show
ministered placebo. Alternatively, if testosterone causes status- thatthisincreasingrateofpunishmentwithofferamountwasre-
enhancingreactiveaggressionbutdoesnotcausenonaggressive strictedtobelow-averageofferamounts(SIResultsandTableS3),
11634 | www.pnas.org/cgi/doi/10.1073/pnas.1608085113 Dreheretal.
Fig.2. Treatmentwithtestosteroneinfluencedpun- A B
ishmentandreward.(A)Barplotofparticipants’pro-
portionofchoicestoreward(blue)andpunish(red)
theproposerasafunctionoftheamountofferedto
the participant for the placebo (pale) and testos-
terone (dark) groups. Treatment with testoster-
one increased rates of punishment (main effect:
β=0.70, SE=0.32,  P=0.03; interaction with offer
amount:β=0.18, SE=0.04, P<0.001)aswellasratesof
reward of large offers (β=0.41, SE=0.03, P<0.001),
with increasing testosterone levels specifically associ-
atedwithincreasedratesofpunishmentoflowoffers
(β=−0.40, SE=0.10,  P<0.001)(TableS2)andreward
ofhighoffers(β=0.64, SE=0.12,  P<0.001).(B)Barplotoftheaveragemagnitudesofreward(blue)andpunishment(red)thatparticipantschoseasafunction
ofofferamountfortheplacebo(pale)andtestosterone(dark)groups.Linearregressionsofthesechoicesrevealedasignificanteffectoftheinteractionof
treatmentgroupandofferamountontheamountthattheyrewardedtheproposer(β=0.15, SE=0.07, P=0.03).Specifically,increasingtheamountofferedto
theparticipantwasassociatedwithagreaterincreaseinrewardmagnitudeamongthoseadministeredtestosteronethanamongthoseintheplacebogroup.This
effectwasalsoassociatedspecificallywithincreasedlevelsoftestosterone(β=0.46, SE=0.16, P=0.004).Wefoundnosignificantmainorinteractioneffectsof
treatmentgrouponpunishmentmagnitude.AllerrorbarsrepresentSEM.P,placebo;T,testosterone.
indicatingthattreatmentwithtestosteronedidindeedselectively We indeed found that, when choosing whether to punish or
increasepunishmentofunfairoffers.Wefoundapositiveeffect reward their proposer, those with high levels of testosterone
oftheinteractionbetweentreatmentgroupandamountoffered weremoresensitivetotheamountofferedbytheproposer,such
onrewardrate(β=0.41, SE=0.03, P<0.001),suchthatthosein that they were more likely to punish below-average offers
thetreatmentgroupweremorelikelytorewardhigheroffersthan (β=−0.40, SE=0.10, P<0.001) (Table S2) and more likely to
thoseinthecontrolgroup.Takentogether,theseresultsindicate reward above-average offers (β=0.64, SE=0.12, P<0.001) as
thattreatmentwithtestosteroneinfluencedratesofbothpunish- measured by separate binary probit regressions of choices to
mentandreward. punish and choices to reward. This effect of the interaction be-
When participants indicated that they wished to reward or tween offer amount and testosterone level was present whether
punish theirproposer,theysubsequentlychosethemagnitude of choicestopunishorrewardtheproposerweremodeledusinga
that punishment or reward. Our regression analyses of these singleorderedprobitmodel orseparatebinaryprobitmodels.
choicesrevealedasignificanteffectoftheinteractionoftreatment We also found that those with high testosterone levels were
group and the amount offered to the participant on the amount more sensitive to the amount offered when choosing the mag-
that they rewarded the proposer (β=0.15, SE=0.07, P=0.03) nitude of punishment (β=0.85, SE=0.26, P=0.001) and re-
(Fig.2BandTableS4).Specifically,increasingtheamountoffered ward (β=0.46, SE=0.16, P=0.004), responding to low offers
totheparticipantwasassociatedwithagreaterincreaseinreward withpunishments ofgreatermagnitude andhighoffers withre-
magnitude among those administered testosterone than among wardsofgreatermagnitude(TableS4).
those inthe placebo group. Wefound no significant mainorin- Incontrast,theeffectsofparticipants’estradiollevelsthatwe
teractioneffectsoftreatmentgrouponpunishmentmagnitude. found were antagonistic to those of testosterone (Tables S2
Importantly,alleffectsoftestosteronetreatmentthatwefound and S3), reducing the effect of the amount offered on both
in our previous analysis survive the inclusion of regressors rep- the rate (β=−0.35,  SE=0.05, P<0.001) and magnitude
resenting treatment belief anditsinteractionwithoffer amount. (β=−0.33, SE=0.14, P=0.02) of punishment and the rate
Theinclusionoftheseregressorsalsorevealeddistincteffectsof (β=0.22, SE=0.05, P<0.001)andmagnitude(β=−0.33, SE=
treatmentbeliefonparticipants’behavior(SIResultsandFig.S3). 0.13, P=0.01)ofreward.Thosewithhighlevelsofestradiolwere
lesslikelytopunishandrewardlowandhighoffers,respectively,
EffectsofTreatmentAreAttributabletoTestosteroneandEstradiol. andwhentheydid,theychosepunishmentandrewardamountsof
Ouradministrationoftestosteronewassuccessfulinproducinga lessermagnitude.
clear increase in the serum testosterone levels of the experi- NDES
AC
mgreeefnlnetceatsletrdgardioniuopal.cbHoynotcwhoeemveeitrna,znyttemsrtiesoesatrienormotnhaeetaiessset,croaandviroeelrlatleteidvoentlosshotihpfeptahersatttircoiis-- iwEnnidtdhiocgabetoentohtuhsiantTciernsectaorsesetadesrionpnguenmiPsahrlemedsei’cnttestsoEtofffseutcentrsfoa.niArelotlehffvoeeurlsgshwanatdhsearsseesworacerisadutelotdsf OLOGICALTIVESCIEN
pantsinourtestosteronegrouprelativetothoseinourplacebo high offers, our manipulation raised testosterone to supra- HNI
group (SI Results). This relationship between testosterone and physiological levels. It is possible that testosterone only influ- PSYCCOG
estradiol has led to suggestions in the literature that certain encesthesebehaviorswhenitreacheslevelsnottypicallyseenin
physiologicaleffectspreviouslyattributedtotestosteronemay,in youngmales.Toassesswhetherthisassociationispresentamong
fact,bemediatedbyestradiol(34). those with typical hormonal levels, we repeated our analyses of
To assess whether the behavioral effects of our manipulation punishment and reward behavior including only participants
should be attributed to increases in the testosterone levels of fromthe placebogroup.
those in the treatment group, their raised estradiol levels, or We found that those in the placebo group with high levels of
both, we reanalyzed participants’ choices. We included regres- testosteroneweremorelikelytobothpunish(β=26.10, SE=9.41, 
sorsrepresentingtheirlevelsoftestosteroneandestradiolmea- P=0.006)andreward(β=32.02, SE=11.72, P=0.007)theirpro-
suredimmediatelybeforetheyperformedthetaskaswellastheir poserthanthosewithlowlevelsoftestosterone(Fig.S4andTable
levelsof testosteronemeasuredduringtheirmedicalscreeningto S2). These effects indicate that, even among those with typical en-
accountforanyeffectsofbaselinetestosterone.Accordingtotes- dogenouslevels,hightestosteroneisassociatedwithincreasedrates
tosterone’sproposedroleindrivingstatus-enhancingbehaviors,we of both retaliation and generosity. We did not find an effect of
would expect to find that increasing testosterone levels would be testosterone within the placebo group on the magnitudes of
associatedwithincreasingpunishmentoflowoffersandrewardof punishmentorrewardchosenbyparticipants(TableS4).However,
high offers after accounting for the effects of other hormonal these regressions were carried out with a smaller number of ob-
measurements. servations,beingrestrictedtonotonlytheplacebogroupbutalso,
Dreheretal. PNAS | October11,2016 | vol.113 | no.41 | 11635
the subset of trials in which participants first chose to punish or Theincreasethatweobserveinrewardoflargeoffersdoesnot
rewardtheproposer.Therefore,thenulleffectsthatweobtainmay seem to result from an enhancement of their hedonic value,
beattributabletoalackofpower(effectsofestradiolarediscussed because participants treated with testosterone do not accept
inSIResults). largeoffers more frequently or morerapidly than thosetreated
with placebo. The choices of participants’ between monetary
Discussion gambles in the nonsocial certainty equivalents task were also
In this study, we sought to expand on what is known about the unaffected by treatment. Thus, it seems that testosterone specif-
influence of testosterone on male social behavior. Although ically altered the social motivations underlying participants’
empirical research and popular opinion center on its role in behavior.
driving aggressive and antisocial behaviors, direct causal evi- Although the double-blind, placebo-controlled treatment
dence for this link is weak in men (11, 12, 35). Some have sug- procedureisavitaltoolfordeterminingwhetherhormonesexert
gested (12, 28, 29) that testosterone instead promotes both a causal influence on human behavior (28), it is not without
aggressive andnonaggressive behaviors that enhance andmain- potential limitations. We performed a number of precautionary
tainsocial status. Here, weexperimentally manipulated the tes- analyses not previously used in the literature to determine the
tosterone levels of young males and tested the fundamental robustnessofourresults.
predictions of these theories against behavior in a two-player First, testosterone is converted to the estrogen estradiol by
economicbargaininggame. aromatase,whichhasledtosuggestionsthatsomeeffectsoftes-
We found that administration of testosterone caused partici- tosterone administration may be mediated by raised estradiol
pants to punish their opponents more frequently than those levelsand not bytestosteroneper se (34,36). Wefound that,in
administered placebo and that higher testosterone levels were additiontoraising theirlevelsoftestosterone, administering tes-
specifically associated with increased punishment of opponents tosteronetoourparticipantsindeedcausedaconcomitantrisein
whomadeunfairoffers.Importantly,thispunishmentwascostly theirestradiollevels.However,byincludingparticipants’hormone
to the participant and could not be used as an instrument to levelsascovariatesinourbehavioralanalyses,weconfirmedthat
coerce their opponent into offering them larger amounts, be- greaterpunishmentofunfairoffersandrewardofgenerousones
causetheiropponents’behaviorwasknownbyparticipantstobe areattributabletoparticipants’testosteronelevelsandnottotheir
predetermined. Thus, unlike previous studies, we can conclude levelsofestradiol.Infact,theeffectsofestradiolwereantagonistic
thattestosteronecanindeedcausemaleaggression(13)andthat tothoseoftestosterone,withincreasedestradiollevelsassociated
this aggression was not mediated by an increased motivation to withareductionintherateandmagnitudeofbothpunishmentof
maximize task earnings or altered beliefs about the strategic unfairoffersandrewardofgenerousoffers.
influence oftheir actionsonothers(33). Second,weshowthathighlevelsoftestosteroneamongthose
Testosterone has been suggested to selectively potentiate in the placebo group were associated with higher rates of both
aggression that is reactive, or in response to provocation (30). punishment of proposers who made low offers and greater
Ourresultssupportsuchaninterpretation,showingthat,inthe generositytowardthosewhomadelargeoffers,showingthatthe
absence of provocation, as when they received large offers, behavioral effects that we observe are not limited to the supra-
participants in the treatment group were not less likely to re- physiological levelsoftestosterone causedbyourtreatment.
wardtheseoffersthanthoseinthecontrolgroup.Ratherthan It should be noted that, although correlating participants’
givingrisetoindiscriminateaggression,testosteroneseemedto choiceswiththeirperipherallevelsoftestosteroneandestradiol
intensify aggression in social contexts where social status may providesinsightintotheroleofeachindrivingbehavior,future
be under threat. This effect is consistent with the idea that research on testosterone would benefit from the use of a hor-
testosterone-inducedaggressionmaybeatooltoachievesocial monal manipulation that does not perturb estradiol levels. One
dominance and garner reproductive opportunities (13). possibility for future studies would be to suppress the conver-
However, our results indicate that testosterone’s influence on sion of testosterone to estradiol with the administration of an
male social behaviorisnot limitedtoreactive aggression.Partic- aromataseinhibitor.
ipantswhoreceivedtestosteronewereinfactmorelikelytooffer Although this study is one of the only placebo-controlled
monetary rewards toproposers whooffered them largeamounts pharmacological studies focusing on the role of testosterone in
ofmoney.Furthermore,theychoserewardsofgreatermagnitude male behavior, the effects of testosterone on women’s behavior
thanthoseadministeredplacebo.Again,thetaskdesignexcludes havereceivedconsiderablymoreexperimentalattention(12,37–
thepossibilitythat thisbehaviorcanbeinterpretedasbeing mo- 39).Ithasbeenarguedthattestosteronemayalsopromotestatus
tivatedbyastrategicintentiontoinfluencetheiropponents’future concerns in women (33, 39, 40), and a number of studies has
offers.Thisincreaseingenerosityrepresentsademonstrationthat shown that testosterone’s effects in women are not limited to
testosterone can cause male behavior that is prosocial or bene- promotingaggression(38–40).Infact,ourstudyextendstomen
ficialtoothers.Inaddition,thisbehaviorsatisfiesadistinguishing recent findings suggesting that testosterone has important pro-
prediction of the status theory of testosterone (28), namely that socialeffectsbyincreasingcooperationinthepublicgoodsgame
testosteroneshouldstimulatenonaggressivebehaviorsinmalesif, (38)andincreasinggenerositywhenrepayingtrust(39).Thereis
likegenerosity,thosebehaviors arestatusenhancing. someevidence,however,thattheremaybesexdifferencesinthe
The increase that we observe in both punishment of small effectsoftestosterone.Althoughinmales,testosteronehasbeen
offers and reward of large offers may raise the concern as to associated with decreased UG offers (10), administering testos-
whether administration of testosterone caused participants to terone to women increases (39) or does not change (37) UG
simply become more impulsive. However, we found that our offers. In addition, sex differences have been observed in the
treatmenthadnoeffectontheimmediatedecisionofwhetherto responsivenessoftestosteronelevelstosocialstimuli(41).These
reject the offer, which they made before deciding whether to findings may reflect fundamental differences in the function of
punishorrewardtheproposer.Treatmentwithtestosteronealso testosteroneinmen andwomen ordifferencesbetween thegen-
had no effect on the speed with which participants chose to ders inthe behaviors that are considered to increase status (42).
punishorrewardtheproposer(SIResults,Fig.S5,andTableS5). Alternatively,wesuggestthat,inthelightofourresults,someof
The absence of an effect on reaction times suggests that testos- thesexvariabilityintheeffectsoftestosteronemaybeattributable
terone does not simply enhance general emotional responsive- totypicallyunmeasuredeffectsofestradiol.
ness but has a more restricted effect that is consistent with Neuroimaging studies have associated elevated testosterone
increasingstatus-enhancingaggressiveandnonaggressivebehaviors. withexaggeratedbloodoxygenleveldependent(BOLD)responses
11636 | www.pnas.org/cgi/doi/10.1073/pnas.1608085113 Dreheretal.
inamygdala(43–45)anddecreasedamygdala–orbitofrontalcortex giventheopportunitytosplitasumofmoney(Fig.1).Here,participants
(OFC)couplingduringprocessingofangryandfearfulfacial always assumed the role of the responder and played with one of four
expressions (46, 47), with these mechanisms being suggested to proposersoneachtrial.ParticipantswereendowedwithV10thattheycould
mediate recruitment of aggressive behavior by testosterone in use during the game. Participants were explicitly instructed that the pro-
posers’offerswereprerecordedandtherefore,independentofthechoices
responsetosuchthreateningsocialstimuli(48).Oneinteresting
oftheparticipant.ThesumofmoneytobedividedwasfixedatV12onall
question for future research is whether this pathway may also
trials.ThefirstproposeralwaysofferedV2,V3,orV4;thesecondproposer
mediate the prosocial effects of testosterone that we observed alwaysofferedV5,V6,orV7;andthethirdproposeralwaysofferedV8,
given that the roles of amygdala and OFC in regulating social V9,orV10.Afourthproposerwasassociatedwithacontrolcondition,in
behavior are not limited to aggression (49, 50). Estrogen re- which the participant was instructed in the responses that they should
ceptors are also known to be present in amygdala and other make.Asmallnumber(3of40)ofparticipantsplayedthetaskwithout
components of the reward system (51, 52), suggesting that tes- thesecontroltrials.
tosterone and estradiol might influence behavior by binding to Everytrialbeganwiththepresentationoftheimageofaproposeralong
their respective receptors in the same set of neural structures. withtheoffertosplitthesumofmoneyshownbothintextformandusinga
Alternatively, given the opposing behavioral effects of estradiol coloredhorizontalbar,wheretheproportioncoloredyellowindicatedthe
and testosterone in this task, estradiol may have influenced be- proportionofthesumbeingofferedtotheresponder.Theresponderschose
haviorinthetaskbyreducingtheactivityofandrogenreceptors oneoftworesponses:acceptorreject.Iftheychosetoaccept,thesumof
by binding to the receptor (53) or down-regulation of receptor moneywasdividedaccordingtotheoffer,whereasiftheychosetoreject,the
sumofmoneywasreturnedtotheexperimenter.Afteravariableduration
expression(54, 55).
interstimulusinterval(ISI)[∼U(2,5)]andirrespectiveofwhethertheyhad
Evolutionary game theories have established how the combi-
chosen toacceptorreject the offer,responders werethen given theop-
nation of two types of incentives (rewards and punishments) is
portunitytopunishorrewardtheproposerbyincreasingordecreasingthe
efficient to lead to a population where defectors are punished proposer’spayoutforthetrial.Participantscouldalsochooseto“donoth-
and cooperation is promoted (56). Our study suggests that tes- ing”andleavetheproposer’searningsunchanged.Iftheychosetopunishor
tosterone, by playing on both positive and negative incentives, reward,theyspecifieditsmagnitude(V2,V4,V6,orV8)atthefollowing
couldhaveplayedakeyevolutionaryroleinnotonlypromoting screen.Thecostofpunishment/rewardtotheparticipantwassetat1/5ofits
aggressive behavior but also, increasing generous behavior to magnitude.Finally,participantswereshowntheirnetwinningsandthoseof
maintain a high social status. Observations in nonhuman pri- theproposerforthetrialfor3s.Eachtrialwasfollowedbyavariabledu-
matesalsoindicatethatthesocialhierarchymaybemaintained rationintervalintertrialinterval(ITI)[∼U(2,5)].Nomaximumresponsetimes
by alpha males—having higher testosterone levels (57)—by not wereenforced.Participantswhoplayedthetaskwithcontroltrialscompleted
108trials,whereasthosewithoutcontroltrialscompleted90trials.Becauseof
only aggressive behavior but also, sharing resources, such as
technicalproblems,twoparticipantscompleted60and72trials,respectively.
accesstofood andfemales.
Aftercompletingthetask,participantsreceivedtheirV10endowmentplus
Our findings flatly contradict a simple link between testos-
thesummedearnings/lossesfromthreerandomlyselectedtrials.
teroneandmaleaggression,atheorythatwouldhavepredicted
increasedrejectionandpunishmentofunfairoffersandreduced BehavioralDataAnalysis.Participants’choicesinthemodifiedUGtaskwere
reward of generous offers in those who had received testoster- analyzedusingmixedeffectsregressionanalysesinR3.0.3(59),withpar-
one.Instead,wefindthattestosterone’seffectonmalebehavior ticipant identity modeled as a random intercept effect. Our first set of
depended on the social context, and we show in a single exper- analysesmodeledthefollowingasfixedeffects:offeramount[centeredto
iment that testosterone can enhance both reactive aggression themean(V6)],participants’treatmentgroup(testosterone=1,placebo=
andgenerosity.Thispatternofbehaviorcannotbeexplainedby 0),thetreatmentgroupthattheybelievedtheyhadbeenassignedto(tes-
alteredstrategicbeliefs(33)andisconsistentwithtestosterone’s tosterone=1,placebo=0),andtheinteractionsofthetwopreviousvari-
proposed role in promoting male behaviors that will increase ableswithofferamount.Oursecondsetofanalysesmodeledthefollowing
socialstatus(58),providing causalevidenceforthistheory. as fixed effects: offer amount [centered to the mean (V6)], participants’
levelsoftotaltestosteroneandestradiolatthetimeoftesting,theirbaseline
MaterialsandMethods levels of total testosterone measured at screening (Appointment 2), the
treatmentgroupthattheybelievedthattheyhadbeenassignedto,andthe
Participants. Forty-seven participants were recruited by advertisements
interactionsofthepreviousfourregressorswithofferamount.Ourthirdset
postedatTrinityCollegeDublinandSt.James’sHospital.Thestudywas
of analyses used the same model as the second set but was restricted to
approved by two local ethics committees (Trinity College Dublin and
participantsintheplacebogroup.
St. James’s Hospital) in accordance with the Declaration of Helsinki, and DS
writteninformedconsentwasobtainedfromallparticipants.Fourpartici- Participants’ accept/reject responses to each offer were modeled with ANNCE
sdpwp(Meilahcexn)aotutita=oseplndawo2.s(1resFnie.roe2ed=nr5tt,sye2acxS)trr.ciDeiolgeunhn=dstie-nwh2dg.ae9nars7eufd]tbeehcsdreoetmqhcelueripnoealienlsctetthaexllyydusawmctlrihete(enhnedn=[sraitenug3wgde7,ys)f,.wrfborPhoimasemerrtxetiuhc1aiae8splastt(tnohnutrds3e=’y0es1beyp),elafofo-rolrtrderi;cenpimoopctaroetnmiaentnds-- mcmmmmhiiieioxxxxnieeeectddddeoseeeertfffforffffeeeeepwccccuttttassssnrpipdlosirrnhrooade,bmbeadiirrtooteurrdrneeenogggtptrrrhraeeeoissssnbssswigiiiooot,ennnolrleriiinangnrsertellwthmmshesaeeeiroil44drmn.,rteaTehi4nnhaedecpirttaihStopcheanrketoatoitpergirmoredftsiihenen(6swraa0lwlwa)ci;peethteraroheecieakcmmipaerpgososredduooeebfx(lls6eiepem1dduq)anuwwtaieisiionttnhhhndt- PSYCHOLOGICALCOGNITIVESCIE
implementedbythelmerTestpackage(62)wasusedtoobtainPvaluesafter
mixedeffectslinearregressioninlme4.
Overview. Participants who completed the study attended a total of five
appointments, detailed below, at which they provided their consent to
participate, were screened medically by a clinician, received injections of ACKNOWLEDGMENTS.WethankPierreWydoodtforhisassistancewiththe
earlystagesofdataanalysis. ThisresearchwasfundedbytheFP7-People
testosteroneorplaceboinadouble-blindprocedure,completedbehavioral
Intra-EuropeanFellowship235076(toJ.-C.D.).Itwasalsoperformedwithin
testing,andattendedtheclinicianforafinalcheck-up.Additionaldetailsare
theframeworkoftheLaboratoryofExcellence(LABEX)ANR-11-LABEX-0042
inSIMaterialsandMethods. ofUniversitédeLyonwithintheprogramInvestissementsd’Avenir(ANR-11-
IDEX-0007) operatedby the French National Research Agency (toJ.-C.D.).
Modified UG. Participants played a modified version of the UG, a simple ThisworkwasalsosupportedbygrantsfromtheAgenceNationalepourla
economicgameinwhichtwoplayers,theproposerandtheresponder,are Recherche(ANR’BrainChoice’n°14-CE13-0006)(toJ.-C.D.).
1. WilsonJD,GeorgeFW,GriffinJE(1981)Thehormonalcontrolofsexualdevelopment. 3. Allee WC, Collias NE, Lutherman CZ (1939) Modification of the social order in
Science211(4488):1278–1284. flocks of hens by the injection of testosterone propionate. Physiol Zool 12(4):
2. GoyRW,BercovitchFB,McBrairMC(1988)Behavioralmasculinizationisindependent 412–440.
ofgenitalmasculinizationinprenatallyandrogenizedfemalerhesusmacaques.Horm 4. MitchellD(2008)TradingonTestosterone.NYTimes.Availableatwww.nytimes.com/
Behav22(4):552–571. 2008/04/19/business/19online.html.AccessedNovember13,2015.
Dreheretal. PNAS | October11,2016 | vol.113 | no.41 | 11637
5. Antonakis J (2014) Does Power Lead to Corruption? The Guardian. Available at 43.DerntlB,etal.(2009)Amygdalaactivitytofearandangerinhealthyyoungmalesis
https://www.theguardian.com/sustainable-business/2014/dec/17/does-power-lead-to- associatedwithtestosterone.Psychoneuroendocrinology34(5):687–693.
corruption-research-testosterone.AccessedNovember13,2015. 44.HermansEJ,RamseyNF,vanHonkJ(2008)Exogenoustestosteroneenhancesre-
6. RadaRT,LawsDR,KellnerR(1976)Plasmatestosteronelevelsintherapist.Psychosom sponsivenesstosocialthreatintheneuralcircuitryofsocialaggressioninhumans.
Med38(4):257–268. BiolPsychiatry63(3):263–270.
7. DabbsJM,Jr,FradyRL,CarrTS,BeschNF(1987)Salivatestosteroneandcriminal 45.BosPA,vanHonkJ,RamseyNF,SteinDJ,HermansEJ(2013)Testosteroneadministrationin
violenceinyoungadultprisoninmates.PsychosomMed49(2):174–182. womenincreasesamygdalaresponsestofearfulandhappyfaces.Psychoneuroendocrinology
8. DabbsJM,Jr,CarrTS,FradyRL,RiadJK(1995)Testosterone,crime,andmisbehavior 38(6):808–817.
among692maleprisoninmates.PersIndividDif18(5):627–633. 46.vanWingenGA,etal.(2009)Testosteroneincreasesamygdalareactivityinmiddle-
9. KouriEM,LukasSE,PopeHG,Jr,OlivaPS(1995)Increasedaggressiverespondingin agedwomentoayoungadulthoodlevel.Neuropsychopharmacology34(3):539–547.
malevolunteersfollowingtheadministrationofgraduallyincreasingdosesoftes- 47.SpielbergJM,etal.(2015)Pubertaltestosteroneinfluencesthreat-relatedamygdala-
tosteronecypionate.DrugAlcoholDepend40(1):73–79. orbitofrontalcortexcoupling.SocCognAffectNeurosci10(3):408–415.
10.ZakPJ,etal.(2009)Testosteroneadministrationdecreasesgenerosityintheultima- 48.CarréJM,OlmsteadNA(2015)Socialneuroendocrinologyofhumanaggression:Ex-
tumgame.PLoSOne4(12):e8330. aminingtheroleofcompetition-inducedtestosteronedynamics.Neuroscience286:
11.EiseneggerC,HaushoferJ,FehrE(2011)Nosoundevidenceforagender-specific 171–186.
effect of testosterone administration on aggressive motivation exists: Reply to
49.AdolphsR(2010)Whatdoestheamygdalacontributetosocialcognition?AnnNY
Josephsetal.TrendsCognSci15(11):510–511. AcadSci1191(1):42–61.
12.EiseneggerC,HaushoferJ,FehrE(2011)Theroleoftestosteroneinsocialinteraction.
50.RushworthMFS,BehrensTEJ,RudebeckPH,WaltonME(2007)Contrastingrolesfor
TrendsCognSci15(6):263–271.
cingulateandorbitofrontalcortexindecisionsandsocialbehaviour.TrendsCognSci
13.hAyrcphoetrheJs(i2s.0N06e)uTroessctoisBtieorboenheaavnRdevhu3m0(a3n):3a1g9g–r3e4s5si.on:Anevaluationofthechallenge 11(4):168–176.
14.WingfieldJC, HegnerRE,DuftyAM, Ball GF(1990)The“ChallengeHypothesis”: 51.nNoedweminanthSeWm(1a9m9m9)aTlihaenmsoecdiaiallbeexhteanvidoerdnaemtwyogrdka.laAninnmNaYleArecpardodScuic8ti7v7e(1b)e:2h4a2v–io2r5.7A.
Tbhreeeodreintgicastlriamtepgliiceast.ioAnmsfNoartp1a3t6te(6r)n:8s2o9f–t8e4s6to.steronesecretion,matingsystems,and 52.DonahueJE,etal.(2000)Cellscontainingimmunoreactiveestrogenreceptor-αinthe
humanbasalforebrain.BrainRes856(1-2):142–151.
15.SapolskyRM(1991)Testicularfunction,socialrankandpersonalityamongwildba-
boons.Psychoneuroendocrinology16(4):281–293. 53.YehS,MiyamotoH,ShimaH,ChangC(1998)Fromestrogentoandrogenreceptor:A
16.Ruiz-de-la-torreJL,MantecaX(1999)Effectsoftestosteroneonaggressivebehaviour newpathwayforsexhormonesinprostate.ProcNatlAcadSciUSA95(10):5527–5532.
aftersocialmixinginmalelambs.PhysiolBehav68(1-2):109–113. 54.RichterCA,TaylorJA,RuhlenRL,WelshonsWV,VomSaalFS(2007)Estradioland
17.ColliasNE,BarfieldRJ,TarvydES(2002)Testosteroneversuspsychologicalcastration BisphenolAstimulateandrogenreceptorandestrogenreceptorgeneexpressionin
intheexpressionofdominance,territorialityandbreedingbehaviorbymalevillage fetalmouseprostatemesenchymecells.EnvironHealthPerspect115(6):902–908.
weavers(Ploceuscucullatus).Behaviour139(6):801–824. 55.StoverEP,KrishnanAV,FeldmanD(1987)Estrogendown-regulationofandrogen
18.HarbaughWT(1998)Whatdodonationsbuy?:Amodelofphilanthropybasedon receptorsinculturedhumanmammarycancercells(MCF-7).Endocrinology120(6):
prestigeandwarmglow.JPublicEcon67(2):269–284. 2597–2603.
19.AndersonC,KilduffGJ(2009)Thepursuitofstatusinsocialgroups.CurrDirPsychol 56.SigmundK(2007)Punishorperish?Retaliationandcollaborationamonghumans.
Sci18(5):295–298. TrendsEcolEvol22(11):593–600.
20.NicholsM(2010)PhilanthropyBecomingNewStatusSymbolforWealthy.Reuters.Avail- 57.CzotyPW,GouldRW,NaderMA(2009)Relationshipbetweensocialrankandcortisol
ableatwww.reuters.com/article/us-wealth-philanthropy-status-idUSTRE67A2WB20100811. andtestosteroneconcentrationsinmalecynomolgusmonkeys(Macacafascicularis).
AccessedJanuary18,2016. JNeuroendocrinol21(1):68–76.
21.Fehr E, Fischbacher U (2003) The nature of human altruism. Nature 425(6960): 58.MehtaPH,JosephsRA(2006)Testosteronechangeafterlosingpredictsthedecision
785–791. tocompeteagain.HormBehav50(5):684–692.
22.HardyCL,VanVugtM(2006)Niceguysfinishfirst:Thecompetitivealtruismhy- 59.R Core Team (2014) R: A Language and Environment for Statistical Computing
pothesis.PersSocPsycholBull32(10):1402–1413. (RFoundationforStatisticalComputing,Vienna).
23.IzumaK,SaitoDN,SadatoN(2010)Processingoftheincentiveforsocialapprovalin 60.BatesD,MächlerM,BolkerB,WalkerS(2014)Fittinglinearmixed-effectsmodels
theventralstriatumduringcharitabledonation.JCognNeurosci22(4):621–631. usinglme4.arXiv:14065823.
24.IzumaK(2012)Thesocialneuroscienceofreputation.NeurosciRes72(4):283–288. 61.ChristensenRHB(2013)Ordinal—RegressionModelsforOrdinalData(RPackage,
25.IredaleW,VanVugtM,DunbarR(2008)Showingoffinhumans:Malegenerosityasa version2013.9-30).Availableathttps://cran.r-project.org/web/packages/ordinal/index.
matingsignal.EvolPsychol6(3):386–392. html.AccessedSeptember10,2016.
26.WillerR(2009)Groupsrewardindividualsacrifice:Thestatussolutiontothecollective 62.KuznetsovaA,BrockhoffPB,ChristensenRHB(2013)lmerTest:TestsforRandomand
actionproblem.AmSociolRev74(1):23–43. FixedEffectsforLinearMixedEffectModels(lmerObjectsoflme4Package)(RPackage,
27.MilinskiM,SemmannD,KrambeckH-J(2002)Donorstocharitygaininbothindirect version 2.0-29). Available at https://cran.r-project.org/web/packages/lmerTest/index.
reciprocityandpoliticalreputation.ProcBiolSci269(1494):881–883. html.AccessedSeptember10,2016.
28.MazurA,BoothA(1998)Testosteroneanddominanceinmen.BehavBrainSci21(3): 63.ToledanoR,PfausJ(2006)TheSexualArousalandDesireInventory(SADI):Amulti-
353–363. dimensional scale to assess subjective sexual arousal and desire. J Sex Med 3(5):
29.JosephsRA,NewmanML,BrownRP,BeerJM(2003)Status,testosterone,andhuman 853–877.
intellectual performance: Stereotype threat as status concern. Psychol Sci 14(2): 64.BeckAT,WardCH,MendelsonM,MockJ,ErbaughJ(1961)Aninventoryformea-
158–163. suringdepression.ArchGenPsychiatry4:561–571.
30.JosephsRA,MehtaPH,CarréJM(2011)Genderandsocialenvironmentmodulatethe 65.McNairDM,LorrM,DropplemanLF(1971)ProfileofMoodStates(Educationaland
effectsoftestosteroneonsocialbehavior:CommentonEiseneggeretal.TrendsCogn
IndustrialTestingService,SanDiego).
Sci15(11):509–510.
66.GoldbergLR,etal.(2006)Theinternationalpersonalityitempoolandthefutureof
31.EghreressnivkerabnezhJa,viBolrissanEd,SsohceiaarlddoMmHin(a1n9c7e4)inPmlasamn.aPtseyscthoosstoemronMee:dCo3r6r(e6l)a:4ti6o9n–4w7i5th. ag- public-domainpersonalitymeasures.JResPers40(1):84–96.
67.ChristieR,GeisFL,BergerD(1970)StudiesinMachiavellianism(Academic,NewYork).
32.GüthW,SchmittbergerR,SchwarzeB(1982)Anexperimentalanalysisofultimatum
bargaining.JEconBehavOrgan3(4):367–388. 68.EPyesresnInckdiSvBid,DEyifse6n(1ck):2H1J–,2B9a.rrettP(1985)Arevisedversionofthepsychoticismscale.
33.EiseneggerC,NaefM,SnozziR,HeinrichsM,FehrE(2012)Eiseneggeretal.reply.
Nature485(7399):E5–E6. 69.aBnexckietAyT:,PsEypcshtoeimneNtr,icBprorowpnerGti,eSs.teJeCroRnAsul(t19C8li8n)PAsnychinovle5n6t(o6r)y:8f9o3r–8m9e7a.suringclinical
34.NathanL,etal.(2001)Testosteroneinhibitsearlyatherogenesisbyconversionto
estradiol:Criticalroleofaromatase.ProcNatlAcadSciUSA98(6):3589–3593. 70.FoxCR,PoldrackRA(2009)Prospecttheoryandthebrain.Neuroeconomics:Decision
MakingandtheBrain,edsGlimcherPW,CamererCF,FehrE,PoldrackRA(Academic
35.AlbertDJ,WalshML,JonikRH(1993)Aggressioninhumans:Whatisitsbiological
foundation?NeurosciBiobehavRev17(4):405–425. Press,SanDiego),pp145–173.
36.TrainorBC,MarlerCA(2002)Testosteronepromotespaternalbehaviourinamo- 71.Zigmond AS, Snaith RP (1983) The hospital anxiety and depression scale. Acta
nogamousmammalviaconversiontooestrogen.ProcBiolSci269(1493):823–829. PsychiatrScand67(6):361–370.
37.ZethraeusN,etal.(2009)Arandomizedtrialoftheeffectofestrogenandtestos- 72.SnyderPJ,LawrenceDA(1980)Treatmentofmalehypogonadismwithtestosterone
teroneoneconomicbehavior.ProcNatlAcadSciUSA106(16):6535–6538. enanthate.JClinEndocrinolMetab51(6):1335–1339.
38.vanHonkJ,MontoyaER,BosPA,vanVugtM,TerburgD(2012)Newevidenceon 73.Schürmeyer T, Nieschlag E (1984) Comparative pharmacokinetics of testosterone
testosteroneandcooperation.Nature485(7399):E4–E5. enanthateandtestosteronecyclohexanecarboxylateasassessedbyserumandsali-
39.Boksem MAS, et al. (2013) Testosterone inhibits trust but promotes reciprocity. varytestosteronelevelsinnormalmen.IntJAndrol7(3):181–187.
PsycholSci24(11):2306–2314. 74.VermeulenA,VerdonckL,KaufmanJM(1999)Acriticalevaluationofsimplemethods
40.EiseneggerC,NaefM,SnozziR,HeinrichsM,FehrE(2010)Prejudiceandtruthabout fortheestimationoffreetestosteroneinserum.JClinEndocrinolMetab84(10):
the effect of testosterone on human bargaining behaviour. Nature 463(7279): 3666–3672.
356–359. 75.Colagiuri B (2010) Participant expectancies in double-blind randomized placebo-
41.SalvadorA(2005)Copingwithcompetitivesituationsinhumans.NeurosciBiobehav controlledtrials:Potentiallimitationstotrialvalidity.ClinTrials7(3):246–255.
Rev29(1):195–205. 76.ManningJT,ScuttD,WilsonJ,Lewis-JonesDI(1998)Theratioof2ndto4thdigit
42.vanAndersSM,SteigerJ,GoldeyKL(2015)Effectsofgenderedbehaviorontestos- length:Apredictorofspermnumbersandconcentrationsoftestosterone,luteinizing
teroneinwomenandmen.ProcNatlAcadSciUSA112(45):13805–13810. hormoneandoestrogen.HumReprod13(11):3000–3004.
11638 | www.pnas.org/cgi/doi/10.1073/pnas.1608085113 Dreheretal.
Supporting Information
Dreher et al. 10.1073/pnas.1608085113
SIMaterialsandMethods Appointment 4: Testing. At the fourth appointment, which took
Appointment 1: Consent and Questionnaires. At the first appoint- placeonthefollowingday,bloodsampleswerecollectedforthe
ment, all participants provided written informed consent and measurement of serum testosterone concentrations. These
completedabatteryofquestionnaires,namelytheSexualArousal samples were collected 17.5–20 h after the injection of testos-
andDesireInventory(SADI)(63),theBeckDepressionInventory terone or placebo. All participants were then given oral and
(BDI) (64), the Profile of Mood Status (POMS) (65), the In- written instructions for both the modified UG task (Fig. 1)
ternationalPersonalityItemPool(IPIP)(66),theMachiavellianism (detailed below) and a gambling task not presented here. Par-
inventory (Mach IV) (67), the Eysenck Personality Questionnaire ticipants rated pictures of the proposers’ faces for trustworthi-
Revised(EPQ-R)(68),andtheBeckAnxietyInventory(BAI)(69). ness, dominance, frustration, angriness, friendliness, happiness,
Measurements of probability weighting were obtained by eliciting and attractiveness and played a short practice session before
participants’ certainty equivalents for gambles ðV20, p, 0Þ for all undergoing MRI.The scanning lasted∼80min (15 min ofana-
p∈f0.05, 0.10, 0.25, 0.50, 0.75, 0.90, 0.95, 1.00g using an iter- tomicalimagingand65minoffunctionalimaging),duringwhich
participants completed both the modified UG task and the
ativebisectionprocedure(70).Participantswerepaidtheoutcome
ofarandomlyselectedtrialorV15,whicheverwasgreater. gambling task. After scanning, participants again rated the pro-
posers for trustworthiness, dominance, frustration, angriness,
Appointment 2: Medical Screening. At the second appointment, friendliness, happiness, and attractiveness and completed the
participants were screened by an endocrinologist. Exclusion SADI,theBDI,thePOMS,theIPIP,theMachIV,theEPQ-R,
criteria were active medical disease: history of stroke; epilepsy/ the BAI, and the certainty equivalents task. Participants also
seizure disorder; heart attack; blackouts and episodes of un- reported whether they believed they had received testosterone
explained loss of consciousness; head injury if they had expe- and described the effects that they would expect testosterone
rienced posttraumatic amnesia greater than 24 h; loss of administration to have on themselves and others. Participants
consciousness for more than 1 h; significant posttraumatic se- werepaidtheirsummedearningsfromtheUGtask,thegambling
quelae or any evidence of cerebral damage on the computed task,andtheoutcomeofarandomlyselectedtrialfromthecer-
tomography; clinically significant abnormalities on ECG in- taintyequivalentstaskorV80,whicheverwasgreater.Theanalysis
cluding but not limited to conduction abnormalities; heart rate oftheneuroimagingdatawillbepresentedinaseparatepaper.
lessthan55beatsperminuteasjudgedbytheinvestigator;major
Appointment 5: Medical Follow-Up. Finally, participants attended
psychiatric illness; current intake of psychotropic medications,
the endocrinologist again 4–6 wk after the injection. A physical
benzodiazepines, or corticosteroids; current alcohol abuse/
examination was carried out, and blood samples were collected
dependency; scoring above cutoffs (8) on the Hospital Anxiety
and analyzed for hematocrit, lipid profile, PSA, liver, renal
and Depression Scale (71); any contraindication to taking testos-
profile,andhormonalstatustoassessanypotentialchangesafter
teroneasspecifiedintheSummaryofProductsCharacteristics;were
testosterone administration. Paired sample t tests were used to
orhadbeentakingleuprolideacetate,finasteride,spironolactone,
compare the parameters at baseline and follow-up. There were
or cimetidine; reproductive dysfunction; previous or current
no significant changes in hemoglobin, hematocrit, total choles-
prostatecancer;elevated prostate-specific antigen(PSA)levels;
terolanditsfractions,andPSAconcentrationsaftereitherofthe
abnormal renal or hepatic function tests; sleep apnea; and pre-
injections. Two men enrolled in the study reported pain at the
vious testosterone or other androgen replacement. Three par-
injectionsites,whichfullyresolvedafter2d.Oneparticipantin
ticipants were excluded because of high scores on the Hospital
the placebo group reported increased libido after injection.
AnxietyandDepressionScaleandadvisedtoattendtheirgeneral Participants werepaid V50for attending this appointment.
practitioner. Another participant was excluded because of low
testosteroneconcentrations.Hewasfullyevaluatedinregardsto LaboratoryMeasurements. Using blood samples obtained at Ap-
his hormonal status, his repeat testosterone concentration was pointments2and4,wedeterminedserumconcentrationsoftotal
within normal range, and we arranged to see him again in the testosterone (TT) by the electrochemiluminescence immunoas-
metabolic research unit in 6 mo for additional follow-up. Par- say (ECLIA) kit on a cobas e analyzer (Roche Diagnostic Sys-
ticipantsprovidedbloodsamplesforthemeasurementofserum tems). Serum concentrations of sex hormone-binding globulin
testosterone concentrations. Samples for all participants were (SHBG) were measured by ECLIA kit on a cobas e analyzer.
obtainedbetween8:00AMand9:00AM.Ifcandidatesagreedto Serumalbuminwasmeasuredbycolorimetricassay(ALB2;cobas
participate after being found eligible, they were randomly as- e analyzer). Apparent concentrations of free testosterone (FT)
signedtothetreatment(n=21)orplacebo(n=19)groupina werecalculatedfromvaluesofTT,SHBG,andalbuminusingthe
double-blindprocedureusinganonlinerandomizationprogram method described and validated by Vermeulen et al. (74). Es-
(https://www.randomizer.org/). tradiolwas measuredby ECLIA(cobas eanalyzer).
Blood samples were not obtained from two participants at
Appointment 3: Injection. At the third appointment, participants Appointment2andoneparticipantatAppointment4becauseof
received a single i.m. injection. Participants in the treatment experimentererror.Thoseparticipantsareomittedfromfigures
groupwereadministereda1-mLdoseoftestosteroneenanthate and analyses involving measurements of testosterone at the re-
(250mg;Androtardyl/TestovironDepot),whereasparticipantsin spective time points.
theplacebogroupwereadministered1mLsaline;i.m.testosterone
enanthate is a long-acting ester of testosterone. The pharmaco- Digit Ratio Measurements. To determine whether prenatal hor-
kinetics of testosterone enanthate yields supraphysiological tes- monal exposure was associated with the metabolism of testos-
tosteronelevelsinserum asearlyas2 h afterinjection,reaching terone to estradiol, we recalled participants to obtain their
peaklevelsfourtofivetimesabovebasalbetween8and24hafter second-to-fourthdigitlengthratios(2D:4D);22of37participants
injection(72,73). compliedwiththisrequest(11placeboand11testosterone),and
Dreheretal.www.pnas.org/cgi/content/short/1608085113 1of8
2D:4Dwascalculatedfromadigitalphotographoftherighthand Althoughparticipantsdidnothaveinsightintowhichsubstance
by measuring the length of the index and ring finger from the that they had received, even erroneous beliefs about treatment
ventral proximal crease to the tip of the finger using the GNU can influence task responses (75). This influence is particularly
ImageManipulationProgram(GIMP,version2.8.10).Therater, relevantinthecaseoftestosterone,forwhichthereexistsastrong
whowasblindtothehypothesisandtheparticipants’treatment, folkbelieflinkingittoaggressionandviolence(40).Importantly,
measured 2D:4D twice with a time interval of 1 wk. These two alleffectsoftestosteronetreatmentthatwefoundinourprevious
measurementswerehighlycorrelated(r=0.98,P<0.0001).The analysissurvivetheinclusionofregressorsrepresentingtreatment
meanvalue ofthe two measurements was usedfor analysis. beliefanditsinteractionwithofferamount.Theinclusionofthese
regressorsalsorevealedseveraldistincteffectsoftreatmentbelief
Questionnaires.Wecarriedoutamixeddesignmultivariateanalysis onparticipants’behavior (Fig.S1).
ofvariance(MANOVA)onparticipants’pre-andposttaskratings We found that those who believed that they had received
oftheUGproposers’trustworthiness,dominance,frustration, testosteroneweremorelikelytorejectlowoffers(TableS1),with
angriness, friendliness, happiness, and attractiveness with factors a negative main effect of treatment belief and a positive in-
treatment,time(pre-orposttask),andproposeridentity.Wecon- teraction with offer amount ðβ=0.31, SE=0.13, P=0.02Þ. In
ductedmixeddesignANOVAsonparticipants’scoresontheSADI addition, participants’ beliefs about treatment influenced their
(63),the BDI (64),the POMS (65), the PIP(66), the Mach IV choices of reward magnitude (Table S4), with a negative in-
inventory (67), the EPQ-R (68), and the BAI (69) that were teractionbetweentreatmentbeliefandofferamountonreward
administeredatAppointment1(preinjection)andAppointment amountsðβ=−0.18, SE=0.08, P=0.03Þ.Thus,whenthosewho
4(postinjection) totest foreffects oftreatment. believed that they had received testosterone chose to reward
high offers, they did so with rewards of lesser magnitude than
SIResults
those whohadbelieved that they hadreceived placebo.
Hormone Levels. As illustrated in Fig. S1, baseline serum concen-
tration levels of TT and FT in the treatment [meanTT (MTT) = HormoneLevels Were NotCorrelated with DigitRatio. It has been
21.06nmol/L,SD =5.66;M =0.48nmol/L,SD =0.12]and suggested that the rate of aromatization of testosterone into
TT FT FT
theplacebogroups(M =20.46nmol/L,SD =5.88;M =0.49 estradiol may be related to in utero exposure to sex hormones
TT TT FT
nmol/L, SD = 0.16) did not differ significantly (TT: Mann– (38), with greater exposure to estradiol being associated with
FT
Whitney U = 162, P = 0.64, two tailed; FT: Mann–Whitney U = faster metabolism of testosterone. Relative prenatal levels of
169,P=0.79,twotailed).Incontrast,thepostinjectiontestosterone testosterone and estradiol are thought to influence the hands’
levelsofthetreatmentgroup(M =66.08nmol/L,SD =29.60; 2D:4D, with a high 2D:4D indicating low prenatal testosterone
TT TT
M =1.92nmol/L,SD =0.97)wereelevatedrelativetothoseof exposure relative to estradiol (76). Therefore, to test this hy-
FT FT
theplacebogroup(M =20.44nmol/L,SD =4.10;M =0.45 pothesis, we tested for correlations between participants’ hor-
TT TT FT
nmol/L, SD = 0.08). These differences were statistically signifi- mone levels and their right hands’ 2D:4D. We found no
FT
cant(TT:Mann–WhitneyU=4,P<0.001,onesided;FT:Mann– significantcorrelationsbetweenparticipants’digitratioandtheir
Whitney U = 0, P < 0.001, one sided), confirming the efficacy of levels of TT ðr=−0.002, P=0.99Þ, the change in their TT rela-
treatment. We also found a concomitant increase in the estradiol tivetobaselinemeasurementðr=−0.07, P=0.74Þ,theirlevelsof
levelsofparticipantsinourtestosteronegroup(M=185.38pmol/L, estradiol ðr=−0.02, P=0.99Þ, or the ratio of TT to estradiol
SD = 39.55) relative to those in our placebo group (M = 101.58 ðr=0.13, P=0.57Þ. The same qualitative results are obtained if
pmol/L, SD = 31.05). This difference was statistically significant we restrict the analysis to participants in the placebo or testos-
(Mann–WhitneyU=373,P<0.001,onesided). terone group. Although we find no evidence of a relationship
between digit ratio and hormone levels in this dataset, these
Treatment Selectively Increased Punishment of Unfair Offers. Our analyseswereperformedwithasubsetoftheparticipants(22of
binaryprobitregressionofpunishmentyieldedapositiveeffectof 37), and the absence of a significant effect may, therefore, be
the interaction between treatment group and offer amount, attributable to alack ofpower.
suggesting that participants treated with testosterone were in-
creasingly likely to punish offers of increasing magnitude. We Effects of Endogenous Estradiol. The effects of estradiol in the
performedfollow-upanalysestodeterminewhetherthiseffectof placebo group were similar to those found in previous analyses
treatmentwasrestrictedtounfairoffersorgenerousoffersorifit (Table S2), with estradiol levels reducing the effect of the
was common to both. By performing separate regressions of amount offered on the rates of punishment (β = −0.68, SE =
participants’ choices in response to below- and above-average 0.17, P < 0.001) and reward (β = −0.69, SE = 0.26, P = 0.006)
(V6) offer amounts, we found (Table S3) that treatment influ- andthemagnitudeofrewardchosen(TableS3).Estradiollevels
encedratesofpunishmentforbelow-averageofferamountsonly in the placebo group did not influence choices of punishment
(β=0.26, SE=0.07, P<0.001),withincreasingpunishmentwith magnitude(Table S3).
offer amount for unfair offer amounts below V6, and had no
effectonpunishment ofgenerous offers. Reaction Times. Treatment with testosterone had no effect on
participants’ reaction times in the UG task when choosing to
Beliefs About Treatment Do Not Explain Effects of Treatment. To acceptorrejecttheproposer’offersorwhenchoosingtopunish,
determine whether participants were truly blind to their treat- do nothing, or reward. This absence of a reduction in reaction
mentgroupassignation, weexaminedtheir self-reportedbeliefs times suggests that injection with testosterone did not render
regardingwhethertheyhadreceivedtestosteroneorplacebo;6of participants more impulsive. Treatment also had no effect on
40participants reported believing thatthey hadreceived testos- response speed when choosing the magnitude of reward. Par-
terone.Thislownumbermayresultfromthedifferencebetweenthe ticipants treated with testosterone were slower when choosing
popularbeliefsabouttheeffectsofbehavioranditsactualeffectsas the magnitude of punishment ðβ=−2.16, SE=0.78, P=0.006Þ.
illustratedinthismanuscript.Oftheparticipantswhobelievedthey This difference decreased with decreasing offer amount
hadreceivedtestosterone,onlytwoactuallyreceivedtestosterone. ðβ=−0.53, SE=0.20, P=0.008Þ. However, it is not possible to
Asinapreviousbetween-subjectsdesign(40),participants’beliefs determinewhethertheseeffectsonreaction timewhenchoosing
werenotsignificantlycorrelatedwiththetreatmentthattheyhad themagnitudeofpunishmentaredirectlyattributabletotreatment
actuallyreceived(r=−0.16,P=0.32);therefore,weconcludethat or the greater frequency with which participants in the testoster-
participantswereindeedblindtotheirtreatment. onegroupchosetopunishtheproposer(Fig.S5andTableS5).
Dreheretal.www.pnas.org/cgi/content/short/1608085113 2of8
QuestionnaireMeasures.Todeterminewhethertheeffectsoftreat- thatofthoseinthetreatmentgroup(M=−0.65,SD=3.34).This
ment on participants’ choices were driven by testosterone-induced effect does not survive a Holm–Bonferroni multiple comparisons
biasingoftheparticipants’judgmentsoftheproposers,weanalyzed correctionforthenumberofsubscaleswithinthequestionnaire.We
participants’ratingsoftheproposers’faces.Wefoundnoeffectsof
foundnoeffectsoftreatmentonthedominance,anger,emotional
treatmentonparticipants’ratingsoftheproposers’trustworthiness,
stability,leadership,empathy,risk-taking,anxiety,conformity,social
dominance, frustration, angriness, friendliness, happiness, and at-
confidence,fun-seeking,drive,andreward-responsivenesssubscales
tractivenessmadeimmediatelybeforeandafterperformingtheUG
oftheIPIP;thetension,depression,anger,fatigue,confusion,vigor,
task. We found an effect of treatment on the Machiavellianism
subscaleoftheIPIP,suchthattheaveragechangeinthescoreof ortotalmooddisturbancesubscalesofthePOMS;thepsychoticism,
participants in the placebo group (M = 1.44, SD = 2.62) after extraversion,neuroticism,orliesubscalesoftheEPQ-R;theSADI;
treatmentweregreater[t(35.36)=2.16,P=0.04,twotailed)]than theBDI;theBAI;ortheMachIV.
Fig.S1. Testosteronelevels.BoxplotsummarizingserumconcentrationsofTTatscreening(preinjection)andthetimeofbehavioraltesting(postinjection)in
theplacebo(palegreen)andtestosterone(darkgreen)groups.Boxcenterscorrespondtomedianvalues,boxbottomsandtopscorrespondtothefirstand
third quartiles respectively, and whiskers represent the maximum and minimumconcentrations. Pre- and postinjection testosterone levels did not differ
significantlyintheplacebogroup(Mann–WhitneyU=162,P=0.64,twotailed),butinthetreatmentgroup,postinjectionlevelsweresignificantlyelevated
(Mann-WhitneyU=4,P<0.001,onesided).
Fig.S2. Ratesofofferacceptance.Barplotofparticipants’averageacceptanceratesasafunctionofofferamountfortheplacebo(palegreen)andtes-
tosterone(darkgreen)groups.Offeracceptancewasnotinfluencedbytreatment.
Dreheretal.www.pnas.org/cgi/content/short/1608085113 3of8
Fig.S3. Effectsofparticipants’beliefs.(A)Barplotofparticipants’averageacceptanceratesasafunctionofofferamountforparticipantswhobelievedthat
they had received placebo (pale green) and testosterone (dark green). Participants’ beliefs about treatment interacted with offer amount
ðβ=0.31, SE=0.13, P=0.02Þ,suchthatparticipantswhobelievedthattheyhadreceivedtestosterone(n=6)weremorelikelytorejectlowoffersthanthose
whobelievedthattheyhadreceivedplacebo(n=34).(B)Barplotoftheaveragemagnitudesofreward(blue)andpunishment(red)thatparticipantschoseas
afunctionofofferamountforparticipantswhobelievedthattheyhadreceivedplacebo(pale)andtestosterone(dark).Participantswhobelievedthatthey
had received testosterone reciprocated generous offers with rewards of lesser magnitude than those who believed that they had received placebo
ðβ=−0.18, SE=0.08, P=0.03Þ.Theeffectofparticipants’treatmentbeliefsonpunishmentmagnitudewasnotsignificant.AllerrorbarsrepresentSEM.Be-
lievedP,believedplacebo;believedT,believedtestosterone.
Fig.S4. Hightestosteronelevelsintheplacebogroupwereassociatedwithmorefrequentpunishmentandreward.Barplotoftheproportionofchoicesto
reward(blue)andpunish(red)theproposerasafunctionofofferamountforparticipantsintheplacebogroupwithhigh(dark)andlow(pale)testosteroneas
determinedbyamediansplit.Ratesofbothpunishmentðβ=26.10, SE=9.41, P=0.006Þandrewardðβ=32.02, SE=11.72, P=0.007Þincreasedsignificantly
withtestosterone.HighT,hightestosterone;lowT,lowtestosterone.
Dreheretal.www.pnas.org/cgi/content/short/1608085113 4of8