S teinEr Jak

Ba ningacc plicadev minconMe mildglu ne hcon nsesRe d elcon ditiowaCo strathu ts ofuse s, suc

Kepsy

Sexhleslatede(PTleaprocle

invin anexp(Desiderato and Newman 1971; Maier 1990; Mineka et al 1984;Mocorfeaof ThproditChJachuof emPa

acuhecedlogmein moleasubfunab

wiciahohu(C(K19et the current study.

FroAd

Rec

000dowrer and Viek 1948). The glucocorticoid stress hormoneticosterone (CORT) might be partially responsible, becauser conditioning is also facilitated after acute and chronic dosesCORT in the absence of stress exposure (Conrad et al 2004;ompson et al 2004). Some theoretic approaches to PTSDpose similar stress-induced modulations of human fear con-ioning (e.g., Armony and LeDoux 1997; Bonne et al 2004;arney et al 1993; Elzinga and Bremner 2002; Metcalfe andobs 1998). Although such effects have not been examined inmans, stress exposure has been shown to enhance other formsemotional learning, such as the formation of memories forotionally arousing stimuli (Cahill et al 2003; Jelicic et al 2004;yne et al 2004, in press).The primary aim of this study was to investigate the impact of

Methods andMaterials

ParticipantsNinety-five (50 men, 45 women) undergraduates from the

University of Arizona provided written consent for participationin the study. Forty-seven were randomly assigned to the stressgroup (22 women, 25 men) and forty-eight to the control group(23 women, 25 men). Data from one man in the stress groupwere removed from analyses owing to insufficient skin conduc-tance responses. Written informed consent and study procedureswere approved by the Human Participants Protection Program atthe University of Arizona and conducted in accordance with theHelsinki Declaration of 1975 as revised in 1983 and with HIPAAguidelines.

ProcedurePsychological Stressor. Participants assigned to the stress

group were exposed to a psychological stressor, a 60 minrecovery period, and then a fear conditioning procedure. Partic-

mtheDepartment of Psychology, University of Arizona, Tucson, Arizona.dress reprint requests to W. Jake Jacobs, University of Arizona, Depart-ment of Psychology, Anxiety Research Group, 1503 E. University Blvd.Building 68, Tucson AZ 85721; E-mail: wjj@email.arizona.edu.eived March 28, 2005; revised June 13, 2005; accepted August 2, 2005.

BIOL PSYCHIATRY 2006;59:5165226-3223/06/$32.00i:10.1016/j.biopsych.2005.08.002 2005 Society of Biological Psychiatrytress Differentially Modula Healthy Men and Women

ic D. Jackson, Jessica D. Payne, Lynn Nadel, and W.

ckground: Stress and stress hormones modulate emotional learounts of posttraumatic stress disorder (PTSD), for example, imelopment of intrusive emotional reactions. The present study exaditioned fear in men and women.thods: Ninety-four healthy undergraduates were exposed to acocorticoid stress responses (salivary CORT) were measured. Oditioning procedure while conditioned skin conductance resposults: Exposure to the stressor increased subjective anxiety anditioning; whereas in women, stress appeared to inhibit fear cons associated with increased CORT levels.nclusions: Consistent with animal models, these results demonmans, possibly via hormonal mechanisms. The enhancing effecful model for the formation of pathological emotional reaction

y Words: Posttraumatic stress disorder, classical conditioning,chological stress, glucocorticoids, gender differences, fear

tressful experiences profoundly influence cognitive andemotional functioning, sometimes to a pathological degree.Animals exposed to uncontrollable stressors, for example,

ibit learning alterations that produce fear, anxiety, and help-sness (e.g., Maier 1993). In humans, stress might also modu- emotional learning and, as a consequence, contribute to thevelopment of disorders such as posttraumatic stress disorderSD). This compelling idea has been in the literature for atst 15 years (Pitman 1989); however, the ability of stress toduce alterations in human emotional learning remains un-ar.Fear conditioning is a form of associative learning thatolves the acquisition of fear responses similar to those foundindividuals with PTSD (Armony and LeDoux 1997; Rothbaumd Davis 2003). A number of studies with male rats indicate thatosure to uncontrollable stressors facilitates fear conditionings Fear Conditioning

e Jacobs

in rats and might have similar effects in humans. Theoreticte the stress-induced modulation of fear conditioning in theed the impact of acute stress and cortisol (CORT) on classically

stressor (or control condition) while subjective anxiety andour later, all participants participated in a differential fear (SCR) were recorded.evated CORT levels. In men, stress exposure facilitated fearning. The impact of stress on differential conditioning in men

e that stress exposure can modulate classical conditioning in stress on the formation of conditioned fear might provide ah as those found in PTSD.

te stress on fear conditioning in men and women. To this endalthy undergraduates participated in a fear conditioning pro-ure 1 hour after being exposed or not exposed to a psycho-ical stressor. The secondary aim was to assess potentialdiators such as gender differences and individual differencesstress responsiveness that might identify individuals who arest vulnerable to the stress-induced alterations of emotionalrning. Therefore, we also assessed individual differences injective anxiety and salivary CORT (cortisol in humans isctionally equivalent to corticosterone in rats; thus, both arebreviated as CORT in this article).The results from animal models suggest that fear conditioningll be enhanced in individuals exposed to acute stress, espe-lly those with larger hormonal responses. These studies,wever, have only been conducted with male rats. Studies withmans find significant gender differences in emotional memoryahill 2003; Payne et al, in press), hormonal stress responsesudielka and Kirschbaum 2005), risk of PTSD (Kessler et al95), and the impact of stress on eyeblink conditioning (Shorsal 2000). Therefore, gender differences were also expected in

ipants assigned to the control group began the study with therecovery period, and then proceeded with fear conditioning.Thpro

asstal a jinvwowo5-mbecorpaanas bluThStr199

surpriNElevfor(D30 qutivfeaposubosi(Nsonne

tioet subCOtoranmiingfrostredu(Sa

stre(ormaof Frimoranpapreat twi

unconditional stimulus (UCS) was a 2-sec female scream, gener-ated from a WAV file, amplified to 105 db, and presented throughhethenefacstr

tiowipreanstimsecresThwacoExcotatmetioex

elefirsabChthefinapSCHz(BtheonbeAcrana nPa

Sta

groanwetrosurmogrosubcotheanbataicirniginv

gro

E.D. Jackson et al BIOL PSYCHIATRY 2006;59:516522 517us, the control group was exposed to neither the stresscedure nor a parallel control procedure.The stress procedure was designed to elicit stress responsesociated with anxious anticipation, public speaking, and men-arithmetic. Stressed participants were given 10 min to prepareob speech to be delivered under intense lighting to threeestigators behind a one-way mirror. Participants believed theyuld be video and audio recorded and that their performanceuld be evaluated. In actuality, when participants gave thein extemporaneous speech, there were no investigators

hind the mirror and participants speeches were neither re-ded nor evaluated (Lupien et al 1997). After the speech,rticipants were asked to remain in front of the cameras, lights,d mirror and to count backward from 1022 by 13s as quicklypossible for 5 min. If a mistake was made, the experimenterntly stated, No. That is not correct. Start over with 1022.erefore, the stress procedure was similar to the Trier Socialess Test (TSST), but without a live audience (Kirschbaum et al3; Lupien et al 1997).Recovery Period. A period was scheduled after stress expo-e for the recovery of hormonal elevations that were not ofmary interest, such as adrenocorticotropin hormone (ACTH),, and E (Kirschbaum et al 1993; Richter et al 1996). The CORTels, which were of primary interest, typically remain elevated at least an hour after exposure to a laboratory stressorickerson and Kemeny 2004). The recovery period consisted ofmin of listening to a relaxing CD and 30 min of personalityestionnaires. The questionnaires included the Anxiety Sensi-ity Inventory (ASI), a 16-item questionnaire designed to assessr of anxiety-related symptoms (Reiss et al 1986), the traitrtion of the State-Trait Personality Inventory (STPI Form Y), ajective measure of trait anxiety, depression, anger, and curi-ty (Spielberger 1995), and the NEO Five Factor InventoryEO-FFI) Form S, a self-report measure of the big-five per-ality traits: neuroticism, extraversion, openness, agreeable-ss, and conscientiousness (Costa and McCrae 1992).Measures of Stress Response. There is considerable varia-n in individual responses to psychological stressors (Rohlederal 2003). Hence, it was important to have objective andjective measures of the stress response, including salivaryRT and self-reported anxiety (Spielberger State Anxiety Inven-y; Spielberger 1983). For all participants, saliva samples andxiety reports were collected before the recovery period, 30n into the recovery period, and immediately before condition-. An additional saliva sample and anxiety report was collectedm the stress group immediately before exposure to thessor. All saliva samples were assayed for cortisol content, inplicate, with a commercially available enzyme immunoassaylimetrics, State College, Pennsylvania).Fear Conditioning. Fear conditioning began 60 min after thessor. Two conditioned stimuli (CS) were used in a differential discriminative) conditioning design; one was a picture of an with a fearful facial expression, and the other was a picturethe same man with a neutral facial expression (Ekman andesen 1976). The CSs were presented serially on a computernitor for 2 sec each, with a pseudo-random inter-trial intervalging from 20 sec to 30 sec (mean 25 sec). For eachrticipant, order of CS presentation was randomized by DMDXsentation software (developed by K.I. Forster and J.C. Forsterhe University of Arizona), resulting in a pseudo-random seriesth each CS repeated no more than two times in a row. Theadphones. When presented, the UCS immediately followed termination of one of the pictures, labeled the CS, andver followed the other picture, labeled the CS. The fearfule served as the CS for 47% of control women, 53% ofessed women, 52% of control men, and 48% of stressed men.To habituate participants to the novel stimuli, the fear condi-ning procedure began with each CS being presented oncethout the UCS. Next, acquisition trials consisted of eightsentations of the CS, each followed by the UCS (scream),d eight presentations of the CS alone. Because the inter-ulus interval (ISI) between the CS and the UCS was only 2, there was not enough time to measure skin conductanceponses (SCRs) to the CS before the presentation of the UCS.erefore, after the fourth acquisition trial, an additional CSs presented with no UCS to allow for the measurement ofnditioned SCRs without interference from unconditional SCRs.tinction trials immediately followed the acquisition trials andnsisted of eight presentations of each CS without UCS presen-ion. Because there is no consensus about which is the bestthod to measure the strength of fear conditioning, condi-ned fear was evaluated both during acquisition and duringtinction trials.To measure skin conductance (SC), two Ag-AgCl reusablectrodes (TSD 103, BIOPAC Systems, Goleta, California) weret filled with .05 molar NaCl electrode gel (Discount Dispos-les, Saint Albans, Vermont) as suggested by Venables andristie (1980). The electrodes were then attached by straps to palmar sides of the distal phalanges of the first and secondgers on the left hand. An amplifier (GSR100, BIOPAC Systems)plied a constant voltage to the electrodes to detect changes in. The signal was amplified by 5 S/V, digitized at a rate of 200 and acquired with AcqKnowledge acquisition softwareIOPAC). Skin conductance responses were scored offline as maximal deflection in conductance 1 4 sec after stimulusset (Prokasy and Kumpfer 1973). Trials in which SCRs initiatedfore or after this window were scored as having no SCR.cording to recommendations, the resulting magnitudes werege-corrected (SCR/SCRmax), then log-transformed to better fitormal distribution (Lykken and Venables 1971; Siddle andcker 1987).

tistical AnalysisT tests and Pearson chi-square tests were used to evaluateup differences in sample characteristics. Subjective anxietyd CORT at the three measurements before fear conditioningre analyzed with univariate ANOVAs with stress group (con-l vs. stress) as the between-participant factor (repeated mea-e ANOVAs were not used for this analysis because there werere measurements in the stress group than in the controlup). To determine whether exposure to the stressor elevatedjective anxiety and CORT over baseline, an ANOVA wasnducted with only the stress group, with measurement time aswithin-participant repeated measure. For post hoc analyses,

xiety and CORT change scores were calculated by subtractingseline measurements from the maximum measurement ob-ned after the stress procedure. Given the well-documentedcadian rhythm of CORT release, start time (hours after mid-ht) of the experiment was used as a covariate in all analysesolving CORT (e.g., Van Cauter et al 1996).The conditioning data was analyzed with ANOVAs with stressup (control vs. stress) and gender (men vs. women) as thewww.sobp.org/journal

between-participant factors and with CS-type (CS vs. CS) andblocks of trials (three levels) as the within-participant repeatedmetestrialastiodethehocalrescorme

Re

Sa

wogrothaearalsne

Fear ConditioningThe fear conditioning procedure successfully produced con-

8 11 .99 16 1b 17 11 1b 1

b 1b .93 1

b .7b .61 .6

SE.lwomlisteiatelys or cRT, c

518 BIOL PSYCHIATRY 2006;59:516522 E.D. Jackson et al

wwasure factors. The first block included only the acquisitiont trial; the second trial block included the first four extinctionls (early extinction); and the third trial block included thet four extinction trials (late extinction). To adjust for viola-ns of the sphericity assumption in repeated measure ANOVAs,grees of freedom and probability values were corrected with Geenhouse-Geisser coefficient, when appropriate. For postc analyses and figures, conditioning difference scores wereculated as the mean CS response minus the mean CSponse. Post hoc analyses were conducted with t tests, Pearsonrelations, or pairwise comparisons of estimated marginalans. All analyses used an of .05.

sults

mple CharacteristicsTable 1 shows demographic variables separately for men andmen in stress and control groups. There was a significantup difference in the time at which the study began, indicatingt women in the stress group started the study significantlylier than men in the stress group. Men in the control groupo reported significantly less extraversion and conscientious-ss than men in the stress group.

Table 1. Comparison of Sample Characteristics and StressControl Groups

Men (n 49)

Stress(n 24)

Co(n

Oral Contraceptive use (%)Psychotropic Medication use (%) 8History of Trauma (%) 17Age (yrs) 19.4 .28 20.Start Time (hours after midnight) 13.0a .35 12.Anxiety Sensitivity 33.3 1.7 31.Trait Anxiety 18.0 1.1 20.Trait Depression 16.2 .83 18.Trait Curiosity 28.3 .75 28.Trait Anger 19.4 1.1 20.NEO: Neuroticism 22.5 1.6 26.NEO: Extraversion 35.5a .87 31.2NEO: Openness 28.2 1.2 27.NEO: Agreeableness 25.9 .87 25.NEO: Conscientiousness 35.2a 1.5 30.2State Anxiety at T0 34.8 1.7State Anxiety at T1 45.9a 2.3 35.4State Anxiety at T2 32.1a 1.8 26.7State Anxiety at T3 32.7 1.8 30.Salivary CORT at T0 (nmol/L) 6.4 1.1Salivary CORT at T1 (nmol/L) 9.3a 1.3 6.0Salivary CORT at T2 (nmol/L) 7.1a .85 5.0Salivary CORT at T3 (nmol/L) 4.6 .68 4.

Unless otherwise noted, data are presented as meansstressmenversus controlmen, stresswomenversus controversus control women. Relationships between groups areCORT and State Anxiety measurements were taken immedthe stress or control procedure (T1), 30 min after the strescontrol procedure (T3). NEO, NEO Five Factor Inventory; CO

astress men.bcontrol men.cstress women.dcontrol women.w.sobp.org/journalioned responding, and all conditional responses decreaseder the extinction trials (main effects of trial blocks and-type: all F values 4.9 and p values .01). Stress had anificant gender-specific effect on the emotional responsescited by the CS relative to the CS [stress by gender by-type interaction: F (1,90) 4.3, p .04]. The interactionained significant even after statistically controlling for theture (fearful face vs. neutral face) that was assigned as the [ F (1,89) 4.9, p .03]. Figures 1 and 2, respectively,strate the SCRs during the fear conditioning procedure forn and women.For men, stress exposure significantly elevated emotionalponses to the CS [F (1,47) 5.2, p .03] but not to the CS1,47) .93, p .34]. This enhancement of conditionedponding was detected during each trial block: acquisition testl [F (1,47) 4.8, p .03], early extinction [F (1,47) 4.3, p ], and late extinction [F (1,47) 4.2, p .05] (Figure 1). Postc analyses of the conditioning difference scores confirmed thatferential conditioning, overall, was larger for men in the stressup than for those in the control group [F(1,47) 6.4, p .02].is enhancement of differential conditioning was detected duringacquisition test trial [F(1,47) 5.0, p .03] and during late

onses Among Men and Women in the Stress and

Women (n 45)

pStress

(n 22)Control(n 23)

41 43 ns9 9 ns

27 17 ns2 19.2 .37 19.2 .53 ns1 11.4c .45 12.4 .45 a c.7 34.1 1.6 33.1 1.6 ns.0 19.2 1.3 18.6 .87 ns.1 16.4 1.0 17.2 .93 ns3 29.5 .78 28.3 .69 ns.3 20.6 1.2 17.9 1.0 ns.7 25.7 1.7 25.3 1.7 ns.5 37.7 1.4 37.1d 1.4 a b, b d.2 28.0 1.3 28.1 .97 ns.4 28.2 1.7 28.4 1.4 ns.4 33.9 1.3 33.2 1.2 a b

37.6 2.3 ns.7 45.5c 2.7 38.4d 2.3 a b, c d0 33.0 2.6 29.4 1.5 a b.3 31.5 2.4 32.6 2.3 ns

9.1 1.4 ns2 9.7 1.1 7.9 1.3 a b8 8.9c .98 5.5d .92 a b, c d4 6.5c .71 3.7d .67 c d

The following comparisons were tested with t tests:en, stressmenversus stresswomen, andcontrolmend for the significant (p .05) comparisons. Salivarybefore the stress procedure (T0), immediately after

ontrol procedure (T2), and 60 min after the stress ororticosterone.ditovCSsigeliCSrempicCSillume

res[F (restria.04hodifgroThthe

Resp

ntrol 25)

16125 .75 .48 14 1

extduto dif

or andcontio

wi[F (p Thwo

Un

str

Figconwat te

Figconneva si

E.D. Jackson et al BIOL PSYCHIATRY 2006;59:516522 519inction [F (1,47) 4.2, p .05] but did not reach significancering early extinction [F (1,47) 1.7, p .20] (Figure 1). Exposurethe stressor, therefore, increased conditioned responding andferential conditioning in the male participants.For women, there were no significant group differences in CSCS responses during any of the trial blocks (all F values 2.0 p values .17) (Figure 2); however, post hoc analysis of theditioning difference scores indicated that differential condi-ning was smaller for women in the stress group, compared

ure 1. Magnitudes of skin conductance responses (SCR) to stimuli duringditioned responses to the conditioned stimulus (CS) that was followed by ts never followed by the UCS; Differential, differential conditioned responsest indicated a significant group difference (stress vs. control; p .05).

ure 2.Magnitudes of skin conductance responses (SCR) to stimuli duringditioned responses to the conditioned stimulus (CS) that was followed by theer followedbytheUCS;Differential,differential conditionedresponses, calculatgnificant group difference (stress vs. control; p .05).th women in the control group, during early extinction1,43) 4.0, p .05] but not during acquisition [F (1,43) .01, .92] or late extinction [F (1,43) .95, p .34] (Figure 2).

us, stress appeared to reduce differential conditioning inmen, but only during the first block of extinction trials.

conditional ResponsesStress-related modulation of conditioning might arise fromess-induced changes in unconditional responding (see Jacobs

ear conditioning procedure for men. Error bars indicate the SEs. CS,rtling unconditional stimulus (UCS); CS, responses to the stimulus thatulated as the difference between CS and CS responses. *Two-tailed

ar conditioning procedure for women. Error bars indicate the SEs. CS,ling unconditional stimulus (UCS); CS, responses to the stimulus that wasthedifferencebetweenCSandCS responses. *Two-tailed t test indicatedthe festartedas the fhe stas, calcwww.sobp.org/journal

and Blackburn 1995 for a brief review). In our procedure,unconditional responses to the UCS were represented by SCRs inthepreThpaCSan42.no

An

enThanstre[F (.79difanmethestrecon3.7strerepaftep vsubov can(al

Sa

engromep vgepowoanTathostre60 streelemeenp duindma

nop [F (did

relative to their own baseline [F (1,21) .86, p .37]. The CORTmeasures were not correlated with differential conditioning instr

Ind

featheindwedifananp vde

Di

strRefacmoelethawoanproco

exditindvafeaunforare

uscorepThforEnmeeffbecoadet of are20ho20stuunco

caenwoen

520 BIOL PSYCHIATRY 2006;59:516522 E.D. Jackson et al

ww CS trials during the acquisition phase, because eachsentation of the CS was immediately followed by the UCS.e effects that reached significance were those indicating thatrticipants exhibited the normal pattern of habituation to the/UCS pair but not to the CS (i.e., main effects of CS-typed interaction effects between CS-type and blocks, F values 0 and p values .001). Thus, unconditional responses weret influenced by stress exposure.

xiety ReportsAt the beginning of the study, there were no group differ-ces in anxiety reports (all t values 1.0 and p values .30).e participants in the stress group reported greater subjectivexiety than those in the control group immediately after thessor [F (1,90) 12.78, p .001] and 30 min after the stressor1,90) 6.84, p .01] but not 60 min after the stressor [F (1,90) , p .37]. Although t h e analyses detected no significant genderferences (all F values 2.20 and p values .14), post hocalyses were conducted separately for men and women. Thean levels of subjective anxiety reported by men and women in stress and control groups are included in Table 1. Men in thess group reported greater subjective anxiety than those in thetrol group immediately and 30 min after the stressor [t (47) , p .001; t (47) 2.76, p .01] but not 60 min after thessor [ t (47) 1.1, p .30]. In women, the stress grouported greater anxiety than the control group only immediatelyr the stressor [t (43) 2.0, p .05; all other t values 1.2 andalues .22]. For both men a n d women in the stress group,jective anxiety after the stressor was significantly elevateder baseline [men: F (1,23 ) 18.7, p .001; women: F (1,21 )28.5, p .01]. Subjective anxiety measures were not signifi-tly correlated with differential conditioning in either genderl r values .29 and p values .10).

livary CORTAt the beginning of the study, there were no group differ-ces in CORT (all F values 1.6 and p values .21). The stressup had greater CORT levels than the control group at everyasurement after stress exposure (all F values 4.00 andalues .05). Although the analyses detected no significantnder differences (all F values 1.00 and p values .30),st hoc analyses were conducted separately for men andmen. The mean levels of salivary CORT collected from mend women in the stress and control groups are included inble 1. Men in the stress group had higher CORT levels thanse in the control group immediately and 30 min after thessor [F (1,45) 6.0, p .02; F (1,45) 4.6, p .04] but notmin after the stressor [F (1,45) .60, p .44]. For men in thess group, CORT levels after the stressor were significantlyvated over baseline [F (1,23) 10.6, p .003]. In stressedn, CORT change scores were positively correlated with differ-tial conditioning during the acquisition test trial [r(24) .56, .01] and during late extinction [r(24) .43, p .04] but not

ring early extinction [r(24) .15, p .50]. Thus, the stress-uced enhancement of differential conditioning found in ourle participants was related to CORT responses to the stressor.For women, CORT levels immediately after the stressor weret significantly higher than for the control group [F (1,41) .77, .39] but became elevated 30 min and 60 min after the stressor1,41) 4.9, p .03; F (1,41 ) 6.4, p .02]. Stressed women not, however, exhibit elevated CORT levels after the stressorw.sobp.org/journalessed women (all r values .15 and p values .49).

ividual DifferencesNone of the personality measures were related to differentialr conditioning in stressed men or stressed women. Therefore, measured individual differences did not mediate the stress-uced alterations in emotional learning. Significant correlationsre found, however, in the control group. In control women,ferential conditioning correlated positively with agreeablenessd trait curiosity but correlated negatively with trait anger, traitxiety, trait depression, and neuroticism (all r values .43 andalues .05). Interestingly, no significant correlations weretected in control men or stressed participants.

scussion

This is the first study to investigate the impact of acuteess on classical conditioning in healthy human participants.sults indicated that exposure to a psychological stressorilitated fear conditioning in men but not women. The menst vulnerable to stress-induced facilitation were those withvated CORT levels. Furthermore, there was some evidencet exposure to the stressor suppressed conditioning inmen. The results of the current study are consistent withimal models and are the first to provide support for theposal that stress exposure, even if mild, modulates fearnditioning in humans.Compared with men in the control group, men who wereposed to the psychological stressor evidenced greater con-ioned fear during acquisition and extinction trials. Stress-uced facilitation of conditioning has also been found with ariety of procedures with male rats. For example, contextualr conditioning is enhanced after exposure to acute andcontrollable stressors (Cordero et al 2003; Maier 1990). Otherms of aversive conditioning, such as eyeblink conditioning, also enhanced by stress exposure (Shors et al 1992).Subjective and hormonal measures of stress response wereed to identify individuals in the current study whosenditioning was most affected by stress exposure. Anxietyorts did not predict conditioning in either men or women.us, it is unlikely that generalized arousal was responsible the enhanced fear conditioning in the stressed men.hanced conditioned responding was found, however, inn who had higher CORT responses to the stressor. Theects of stress on fear conditioning, therefore, might haveen mediated by elevated CORT levels. Studies of fearnditioning in male rats, for example, show that CORTministration alone leads to enhanced conditioning (Conradal 2004; Thompson et al 2004). Furthermore, the acquisitioneyeblink conditioning is enhanced 30 min after male rats injected with stress-levels of CORT (Beylin and Shors03). Humans with chronically high exogenous CORT levels,wever, exhibit impaired eyeblink conditioning (Grillon et al04). Because CORT levels in the stressed men of the currentdy were no longer elevated at the time of conditioning, it isclear if CORT was involved in the enhancement of fearnditioning.Gender differences were found in the current study indi-ting that female participants did not exhibit a stress-inducedhancement of conditioning. In fact, during one trial block,men in the stress group exhibited significantly less differ-tial conditioning compared with those in the control group.

The results of the current study add to an accumulatingliterature suggesting that there are significant gender differ-enCaParesencoCOpato

difdifmastimaningstrsoostrbathoThaffhorepoftKirstrCOsigthadiuCaalsbathecobe

dutiothefleof stuacqan

pafeadisfacthefacenenopmeaccPTha

men. Second, the current study assessed fear conditioning 60min after stress exposure, whereas, in PTSD, the stressor isco(Pistrnaelemo

psmoouamfinpathecostra uemde

PepaFoPr

Arm

Bey

Bon

Bre

Cah

Cah

Ch

Co

Co

Co

De

Dic

Ekm

Elz

E.D. Jackson et al BIOL PSYCHIATRY 2006;59:516522 521ces in stress and emotional memory (Breslau et al 1997;hill 2003; Kessler et al 1995; Kudielka and Kirschbaum 2005;yne et al, in press). For example, the current pattern ofults resembles those obtained from rats, showing that stresshances eyeblink conditioning in male rats but impairsnditioning in females (Wood and Shors 1998). In addition,RT was not associated with conditioning in the femalerticipants of the current study, a finding that is also similarfindings in female rats (Wood et al 2001).There are a number of possible explanations for the genderferences in conditioning found in this study. First, theferences might have been related to the stimuli we used,le faces and a female scream. Future studies should useuli that are not gender-biased, such as geometric shapes

d white noise. Second, the gender differences in condition- might have been related to differences in responses to theessor. In men, CORT responses to the stressor peakedner and recovered faster than those in women. In women,ess exposure did not significantly elevate CORT levels overseline, even though levels were significantly larger thanse in the control group at the time of fear conditioning.ese results might indicate that women were not adequatelyected by the stressor. Subjective anxiety reports in women,wever, were significantly elevated and comparable withorts from men. In addition, CORT responses in women areen found to be smaller than those in men (Kudielka andschbaum 2005). The apparent lack of CORT response to theessor might also have been an artifact of elevated baselineRT levels. Women in the stress group started the studynificantly earlier than men in the stress group, suggestingt their CORT levels might have been inflated owing to thernal peak in CORT occurring in the morning (e.g., Vanuter et al 1996). Menstrual cycle and smoking might haveo modulated CORT responses to stress exposure (Kirsch-um et al 1992; Kudielka and Kirschbaum 2005). The lack ofse data in the current study is a weakness that limits anynclusions drawn about CORT responses or the relationshiptween CORT and emotional learning.Our measures of fear conditioning were taken mostlyring extinction trials and, therefore, reflected both acquisi-n and extinction processes. Thus, it could be argued that large conditioned responses found in stressed men re-cted a resistance to fear extinction rather than a facilitationfear conditioning. To better understand these effects, futuredies will need to separate the processes by testing fearuisition during one session and fear extinction duringother.It is tempting to generalize the current findings to thethogenesis of PTSD, given the presumed involvement ofr conditioning in the development and maintenance of thisorder (e.g., Bonne et al 2004). There are a number oftors, however, that limit such a generalization. First, theoretic accounts of PTSD that predict a stress-inducedilitation of fear conditioning do not predict gender differ-ces in this effect. In addition, the pattern of gender differ-ces found in the current study does not reflect the devel-ment of PTSD, which is twice as prevalent in women as inn (Breslau et al 1997; Kessler et al 1995). If this studyurately reflected the pattern of gender difference found inSD, then fear conditioning in the female participants shouldve been more facilitated by stress than conditioning in thencurrent with fear conditioning and typically acts as the UCStman et al 2000). Finally, compared with typical traumaticessors, the stressor used in this study was more social inture, relatively mild, and produced relatively small CORTvations. By ethical necessity, however, any attempts todel PTSD in the laboratory will be limited in similar ways.In sum, we have shown that exposure to a relatively mildychological stressor, accompanied by elevations in CORT,dulates fear conditioning in healthy human participants. Tor knowledge, this is the first study to demonstrate relationsong stress, CORT, and conditioned fear in humans. Thedings confirm the relevance of animal models and providertial support for conditioning-based accounts of PTSD. To extent that the symptomatology of PTSD is related to thenditioned associations formed during acute stress, theess-induced modulation of fear conditioning might serve asseful, yet limited, model for the pathological formation ofotional memories and phobic responses in individuals whovelop PTSD.

This work was supported in part by a grant from McDonnell-w Program in Cognitive Neuroscience awarded to WJJ, and inrt by grants from the McDonnell-Pew Program and the Flinnundation awarded to the Cognition and Neural Systemsogram at the University of Arizona.

ony JL, LeDoux JE (1997): How the brain processes emotional informa-tion. Ann N Y Acad Sci 821:259 270.lin AV, Shors TJ (2003): Glucocorticoids are necessary for enhancing theacquisition of associative memories after acute stressful experience.Horm Behav 43:124 131.ne O, Grillon C, Vythilingam M, Neumeister A, Charney DS (2004): Adap-tive and maladaptive psychobiological responses to severe psychologi-cal stress: Implications for the discovery of novel pharmacotherapy.Neurosci Biobehav Rev 28:6594.slau N, Davis GC, Andreski P, Peterson EL, Schultz LR (1997): Sex differ-ences in posttraumatic stress disorder. Arch Gen Psychiatry 54:1044 1048.ill L (2003): Sex- and hemisphere-related influences on the neurobiologyof emotionally influenced memory. Prog Neuropsychopharmacol BiolPsychiatry 27:12351241.ill L, Gorski L, Le K (2003): Enhanced human memory consolidation withpost-learning stress: Interaction with the degree of arousal at encoding.Learn Mem 10:270 274.arney DS, Deutch AY, Krystal JH, Southwick SM, Davis M (1993): Psycho-biologic mechanisms of posttraumatic stress disorder. Arch Gen Psychi-atry 50:295305.nrad CD, MacMillan DD II, Tsekhanov S, Wright RL, Baran SE, Fuchs RA(2004): Influence of chronic corticosterone and glucocorticoid receptorantagonism in the amygdala on fear conditioning. Neurobiol Learn Mem81:185199.rdero MI, Venero C, Kruyt ND, Sandi C (2003): Prior exposure to a singlestress session facilitates subsequent contextual fear conditioning in rats.Evidence for a role of corticosterone. Horm Behav 44:338 345.sta PT, McCrae RR (1992): Normal personality assessment in clinical prac-tice: The NEO Personality Inventory. Psychol Assess 4:513.siderato O, Newman A (1971): Conditioned suppression produced in ratsby tones paired with escapable or inescapable shock. J Comp PhysiolPsychol 77:427431.kerson SS, Kemeny ME (2004): Acute stressors and cortisol responses: Atheoretical integration and synthesis of laboratory research. Psychol Bull130:355391.anP, FriesenWV (1976):Picturesof Facial Affect. PaloAlto, CA:ConsultingPsychologists Press.ingaBM,Bremner JD (2002): Are theneural substratesofmemory thefinalcommon pathway in posttraumatic stress disorder (PTSD)? J Affect Dis-ord 70:117.www.sobp.org/journal

Grillon C, Smith K, Haynos A, Nieman LK (2004): Deficits in hippocampus-mediated pavlovian conditioning in endogenous hypercortisolism. BiolPsychiatry 56:837843.

Jacobs WJ, Blackburn JR (1995): A model of Pavlovian conditioning: Varia-tions in representations of the unconditional stimulus. Integr PhysiolBehav Sci 30:1233.

Jelicic M, Geraerts E, Merckelbach H, Guerrieri R (2004): Acute stress en-hances memory for emotional words, but impairs memory for neutralwords. Int J Neurosci 114:13431351.

Kessler RC, SonnegaA, BrometE,HughesM,NelsonCB (1995): Posttraumaticstress disorder in the National Comorbidity Survey. Arch Gen Psychiatry52:10481060.

Kirschbaum C, Pirke KM, Hellhammer DH (1993): The Trier Social StressTesta tool for investigating psychobiological stress responses in alaboratory setting. Neuropsychobiology 28:7681.

Kirschbaum C, Wust S, Strasburger CJ (1992): Normal cigarette smokingincreases free cortisol in habitual smokers. Life Sci 50:435442.

Kudielka BM, Kirschbaum C (2005): Sex differences in HPA axis responses tostress: A review. Biol Psychol 69:113132.

Lupien SJ, Gaudreau S, Tchiteya BM, Maheu F, Sharma S, Nair NP, et al (1997):Stress-induceddeclarativememory impairment inhealthy elderly subjects:Relationship to cortisol reactivity. J Clin EndocrinolMeta 82:20702075.

Lykken D, Venables PH (1971): Direct measurement of skin conductance: Aproposal for standardization. Psychophysiology 8:656672.

Maier SF (1990): Role of fear in mediating shuttle escape learning deficit pro-ducedby inescapable shock. J Exp Psychol AnimBehav Process 16:137149.

Maier SF (1993): Learned helplessness: Relationships with fear and anxiety.In: StanfordS, SalmonP,Gray J, editors.Stress: FromSynapse toSyndrome.San Diego, CA: Academic Press 207243.

Me

Min

Mo

Pay

Pay

Pitm

Pitman RK, Shalev AY, Orr SP (2000): Posttraumatic stress disorder: Emotion,conditioning, andmemory. In: GazzanigaMS, editor.NewCognitive Neu-rosciences, 2nd ed. Cambridge, MA: The MIT Press 11331147.

Prokasy WF, Kumpfer KL (1973): Classical conditioning. In: Prokasy WF, edi-tor. Electrodermal Activity in Psychological Research. NewYork: AcademicPress 157202.

Reiss S, Peterson RA, Gursky DM, McNally RJ (1986): Anxiety sensitivity,anxiety frequency and the predictions of fearfulness. Behav Res Ther24:18.

Richter SD, Schurmeyer TH, SchedlowskiM, HadickeA, TewesU, Schmidt RE,Wagner TO (1996): Time kinetics of the endocrine response to acutepsychological stress. J Clin Endocrinol Metab 81:19561960.

Rohleder N, Wolf JM, Kirschbaum C (2003): Glucocorticoid sensitivity inhumans-interindividual differences and acute stress effects. Stress6:207222.

RothbaumBO,DavisM (2003): Applying learningprinciples to the treatmentof post-trauma reactions. Ann N Y Acad Sci 1008:112121.

Shors TJ, Beylin AV, Wood GE, Gould E (2000): The modulation of Pavlovianmemory. Behav Brain Res 110:3952.

Shors TJ, Weiss C, Thompson RF (1992): Stress-induced facilitation of classi-cal conditioning. Science 257:537539.

Siddle DA, Packer JS (1987): Stimulus omission and dishabituation of theelectrodermal orienting response: The allocation of processing re-sources. Psychophysiology 24:181190.

Spielberger CD (1983):Manual for the State-Trait Anxiety Inventory, 2nded. IncollaborationwithGoruschRL, LusheneR, VaggPR, JacobsGA. PaloAlto,CA: Consulting Psychologists Press.

Spielberger CD, Ritterband LM, Sydeman SJ, Reheiser EC, Unger KK

Tho

Van

Ven

Wo

Wo

522 BIOL PSYCHIATRY 2006;59:516522 E.D. Jackson et al

wwtcalfe J, Jacobs WJ (1998): Emotional memory: The effects of stress oncool and hotmemory systems. In:MedinDL, editor. The Psychology ofLearning and Motivation: Advances in Research and Theory, Vol 38. SanDiego, CA: Academic Press 187222.eka S, Cook M, Miller S (1984): Fear conditioned with escapable andinescapable shock: Effects of a feedback stimulus. J Exp Psychol AnimBehav Process 10:307323.wrer OH, Viek P (1948): An experimental analogue of fear from a sense ofhelplessness. Journal of Abnormal & Social Psychology 43:193200.ne JD, Jackson ED, Hoscheidt S, Ryan L, JacobsWJ, Nadel L (in press): Theimpact of stress on neutral and emotional aspects of episodic memory.Memory.ne JD, Jackson ED, Jacobs WJ, Hoscheidt S, Nadel L (2004): Differentialstress effects on memory for emotional and neutral information. Postersession presented at the annual meeting of the Society for Neuro-science, San Diego, CA.an RK (1989): Post-traumatic stress disorder, hormones, and memory.Biol Psychiatry 26:221223.w.sobp.org/journal(1995): Assessment of emotional states and personality traits: mea-suring psychological vital signs. In: Butcher JN, editor. Clinical Person-ality Assessment: Practical Approaches. New York: Oxford UniversityPress 4258.mpson BL, Erickson K, Schulkin J, Rosen JB (2004): Corticosterone facili-tates retention of contextually conditioned fear and increases CRHmRNA expression in the amygdala. Behav Brain Res 149:209215.Cauter E, Leproult R, Kupfer DJ (1996): Effects of gender and age on thelevels and circadian rhythmicity of plasma cortisol. J Clin EndocrinolMetab 81:24682473.ables PH, Christie MJ (1980): Electrodermal activity. In: Venables PH,editor. Techniques in Psychophysiology. New York: Wiley & Sons 467.od GE, Beylin AV, Shors TJ (2001): The contribution of adrenal and repro-ductive hormones to the opposing effects of stress on trace condition-ing in males versus females. Behav Neurosci 115:175187.od GE, Shors TJ (1998): Stress facilitates classical conditioning in males,but impairs classical conditioning in females throughactivational effectsof ovarian hormones. Proc Natl Acad Sci U S A 95:40664071.

Stress Differentially Modulates Fear Conditioning in Healthy Men and WomenMethods and MaterialsParticipantsProcedurePsychological StressorRecovery PeriodMeasures of Stress ResponseFear Conditioning

Statistical Analysis

ResultsSample CharacteristicsFear ConditioningUnconditional ResponsesAnxiety ReportsSalivary CORTIndividual Differences

DiscussionReferences