Pergamon Psychoneuroendocrinology, Vol. 22, No. 8, pp. 615--625. 1997

© 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain

(1306-4530/97 $17.(~) + .00

PII: S0306-4530(97)00072-3

INCREASING CORRELATIONS BETWEEN PERSONALITY TRAITS AND CORTISOL STRESS RESPONSES OBTAINED BY

D A T A AGGREGATION

Jens C. Pruessner, Jens Gaab, Dirk H. Hellhammer, Doris Lintz, Nicole Schommer and Clemens Kirschbaum

Center for Psychobiological and Psychosomatic Research, University of Trier, Dietrichstr. l(I-I I, D-54290 Trier, Germany

(Received 7 November 1996; in final form 17 July 1997)

SUMMARY

Attempts to link personality traits and cortisol stress responses have often been inconclusive. The aim of this paper was to investigate this association by aggregating cortisol stress responses. Therefore, 20 healthy men were exposed to a task consisting of public speaking and mental arithmetics in front of an audience on five days. Six cortisol levels were measured in relation to the stressful task obtained at lll-min intervals on each day. Psychological assessment included the Questionnaire for Competence and Control (FKK) and the Giessen-Test (G-T). These questionnaires focus on assessing personality traits, i.e. locus of control and self-concept. Areas under the response curve (AUC) of the six cortisol samples were computed to obtain an index of the individual's cortisol stress response on each day. Since novelty is a random situational factor likely to mask individual differences in the stress response, the AUC cortisol stress responses of days two to five were consecutively aggregated, excluding the first day. Scales of the two questionnaires employed did not correlate with the AUC cortisol stress response of the first stress trial. The correlation pattern of the AUC cortisol measures of days two to five with the questionnaire scales was inconclusive. However, significant correlations emerged with an increasing number of cortisol stress responses aggregated. Correlations between the measure of social dominance and aggregated AUC cortisol stress responses rose from r = .47 on day two of the experimental session to r = - . 7 0 after aggregating days two to five. Similarly, measures of locus of control and cortisol stress responses became increasingly correlated with aggregation of several stress exposures. These data provide preliminary evidence for a relationship between questionnaire scales aiming at assessing personality traits and cortisol stress responses uncovered by repeated stress exposure and data aggregation. While novelty may mask the impact of personality on the cortisol stress response on the first exposure, differences in the ability to cope with the stressful situation may lead to different cortisol stress response patterns on subsequent stress exposures. With data aggregation, an association between the trait component of cortisol stress responses and questionnaire scales might be uncovered. For reliable investigation of correlations between personality variables and cortisol stress responses, repeated stress exposure and data aggregation is suggested. © 1997 Elsevier Science Ltd. All rights reserved

Keywords--HPA-axis; Cortisol; Stress response; Coping; Personality traits; Data aggregation.

Address correspondence and reprint requests to: Dr C. Kirschbaum, Center for Psychobiological and Psychosomatic Research, University of Trier, Dietrichstr. 10-11, D-54290 Trier, Germany (Tel: +49 651 975 8624; Fax: +49 651 975 8640).

615

616 J.C. Pruessner et al.

I N T R O D U C T I O N

According to early views by Selye (1936), hypothalamic-pituitary-adrenal (HPA) axis activation occurs unspecifically in response to internal and external stimuli. Mason defined more precisely the situational characteristics that lead to activation of the HPA axis (Mason, 1968). He showed that novelty, predictability, controllability, anticipation of negative consequences, and ego-involvement are involved in adrenocortical activation. His findings were supported by demonstrating novelty effects on HPA axis activity in animals (e.g. Grandin, 1997; Hennessy and Kaplan, 1982; Hennessy et al., 1995; Weinberg and Wong, 1986) as well as in man (Gunnar et al., 1989, 1991; Hubert et al., 1989). Moreover, effects of controllability and predictability were shown in animals (Oitzl et al., 1995; Visintainer et al., 1982) and in man (Dess et al., 1983; Gross et al., 1994; Hyyppa, 1987; Voigt et al., 1990; Weizman et al., 1992; Yehuda et al., 1993), providing evidence for the importance of these situational characteristics in modulating the activation of the HPA system.

Besides situational characteristics, Mason also emphasized the importance of psycholo- gical variables in adrenocortical stress responses. Factors he considered to be important were the quality of emotional reactions, effectiveness of psychological defenses, and the acute or chronic nature of the threat (Mason, 1968). Studies investigating these factors reported effects of coping on the HPA axis response to stress (e.g. Bohnen et al., 1991; Houtman and Bakker, 1991; Hyyppa, 1987; Ursin and Olff, 1993; Ursin et al., 1978). According to Henry (1992), successful coping is related to lower adrenocortical responses to stress, while unsuccessful coping is associated with helplessness or hopelessness which leads to higher adrenocortical activity. The use of denial and other defense mechanisms in stressful situations has also been found to be associated with increased adrenocortical activity (Ursin et al., 1978; Vaernes et al., 1982).

In this line of research, several studies tried to uncover possible associations between cortisol stress responses and personality variables. Variables investigated were, e.g. trait anxiety (e.g. Hubert and de Jong-Meyer, 1992; Salmon et al., 1989), extraversion and neuroticism (e.g. Arnetz and Fjellner, 1986), sensation seeking (Kirschbaum et al., 1992), achievement motivation (Lehmann et al., 1992), or locus of control (Seeman et al., 1995). However, the relationship between HPA axis stress responses and personality traits is less consistent, and many studies failed to show effects of personality traits on HPA stress responses (e.g., Blood et al., 1994; Kirschbaum et al., 1992; Salmon et al., 1989; van Eck et al., 1996). One reason for this inconsistency is the fact that the cortisol stress response reflects a state measure, which depends only in part on the personality of the subject, but also on the acquired coping strategies, the probability of success in the given situation, and the relationship between them. Thus, in order to reveal consistent associations between personality traits and cortisol stress responses, the trait component of the cortisol stress response needs to be determined. Within the person-situation debate, Epstein (1986) suggested to average behavior over more than one situation to reveal the existence of broad cross-situational response dispositions. Thus, in order to reveal a cross-situational general component of a cortisol response, repeated stress exposure with subsequent aggregation of the stress responses might reveal a personality trait related endocrine response disposition. Another advantage of repeated stress exposures is that beginning with the second trial, the impact of novelty on the individual stress response is reduced and the association between personality variables and the cortisol stress response might be more easily revealed. Novelty is a situational characteristic that might mask associations between personality traits and cortisol stress responses (Gunnar et al., 1989).

Correlations between Cortisol Responses and Personality Traits 617

The aim of the present paper is to show the effects of data aggregation across repeated stress trials on the association between cortisol stress responses and selected personality variables. A theoretical and empirical framework suggests that self-esteem and locus of control are personality variables that might be linked to adrenocortical stress responses (Henry, 1992; Seeman et al., 1995; Zorrilla et al., 1995). For this reason, questionnaires assessing locus of control and self-concept were employed. Subjects were exposed repeatedly to the same stressor, and cortisol stress responses were aggregated across stress trials. In order to minimize the impact of novelty on the stress response, the first trial was excluded from aggregation. The aggregated cortisol stress responses were then correlated with the personality variables to investigate possible associations. The data on different response patterns of the cortisol responses to repeated stress have been reported elsewhere (Kirschbaum et al., 1995).

METHODS

Subjects Twenty male nonsmokers (mean age 22.4, standard error 2.1 years) were investigated in

this study. All subjects were students from the University of Trier and were paid for participation after attending all experimental sessions. The volunteers were drug-free and reported a good health status. All subjects participated under the same experimental design.

Study Outline Cortisol secretion is characterized by a strong circadian rhythm with peak levels in the

early morning hours (Van Cauter, 1987). Thus, in order to reliably differentiate the stress- induced cortisol secretion from baseline cortisol levels, all experimental sessions were held in the late afternoon. Subjects were told to abstain from physical exercise at least one hour before the experimental session. In addition, they were asked to refrain from drinks with low pH or larger meals immediately before the start of the experimental session.

The general experimental setup was identical on all experimental days. On four consecutive days and a fifth day with a two day interval between days four and five, subjects were exposed to the 'Trier Social Stress Test' (TSST), a tool which consists of public speaking and mental arithmetics in front of an audience and has proven to effectively induce a cortisol stress response (Kirschbaum et al., 1993). The test procedure was the same for all subjects: On arrival, subjects initially rested for 10 min before they were introduced to the stressful task. Following the introduction, subjects were allowed to prepare the public speech for ten min. Thereafter, subjects were exposed to the actual stress session for ten rain. The stress session was followed by a final resting period of 30 min for all subjects. Overall, each session took about one hour each day.

Saliva Sampling and Cortisol Analysis Saliva samples for cortisol assessment were obtained with the 'Salivette' (Sarstedt,

Germany). On each day, six saliva samples were obtained from each subject at 10-min intervals starting after the initial 10-min rest period.

After sampling, cortisol was stored at -20°C until analysis. Cortisol concentrations were determined using a time-resolved fluorescence immunoassay (DELFIA) which is described in detail elsewhere (Dressend6rfer et al., 1992). Intra- and inter-assay variation of the assay were less than 10% and 12%, respectively.

618 J.C. Pruessner et al.

Psychological Assessment The goal of the psychological assessment in this study was to investigate interindividual

differences in self-concept, locus of control and self-esteem. For this reason, two German questionnaires were employed.

In detail, the Questionnaire of Competence and Control (FKK; Krampen, 1991) was used for assessing locus of control and self-concept. The FKK consists of 32 items with six-point response scales ranging from 'completely agree' to 'completely disagree'. It has four subscales 'positive self-concept', 'internality', 'powerful others control', and 'chance'. In this study, the subscale 'positive self-concept' (SC) showed strong reliability (~ = .91) and scores ranging between 29 and 66 scale points (M = 46.82; SD = 11.04) An example for an item of this scale is 'Even in difficult situations I usually have many possibilities'. Subscale 'internality' (INT, e.g. 'I can determine may things that are happening in my life') presented with good reliability (c~ = .83) and scores ranging between 26 and 58 scale points (M = 45.75; SD = 7.69). Subscale 'powerful others control' (POC, e.g. 'My everyday life is determined by other persons in many areas') showed moderate reliability (~ = .62) with scores ranging between 29 and 69 scale points (M = 48.6; SD = 8.86). Subscale 'chance' (FAT, e.g. 'Many events in my life happen by chance') showed good reliability (~ -- .79) with scores between 32 and 69 scale points (M= 48.1; SD = 10.88).

In addition, the Giessen-Test (GT; Beckmann et al., 1991) was used. The GT comprises 40 items that are divided into six subscales, aiming at assessing different aspects of a person's perception of him or herself. It has the same response scale format as the FKK. In this study, the subscale 'social resonance' (GT1, e.g. 'I have the impression that other people think of me as valuable person') showed good reliability (~ = .73), with scale points ranging from 20 to 33 scale points (M = 26.5; SD = 4.3). Subscale 'social dominance' (GT2, e.g. 'I think that in general I am seen as a strong person') also showed good reliability (7 = .76) with scores ranging between 15 and 34 scale points (M=24.09; SD=6.13). Subscale 'control' (GT3', e.g. 'I feel that I have more problems managing my finances than other persons') showed moderate reliability (:~ = .56) with scores ranging between 20 and 35 scale points (M= 27.45; SD = 3.95). Subscale 'general mood' (GT4, e.g. 'I often feel anxious') showed weak reliability (~ = .51) with scores ranging from 10 to 36 scale points (M = 25.1; SD -- 6.6). Subscale 'trustfulness' (GT5, e.g. 'It is hard for me to depend on other people') showed a reliability of ~ -- .68 with scores ranging from 13 and 33 scale points (M = 24.09; SD = 6.13), and subscale 'social potency' (GT6, e.g. 'I think it is easy for me to succeed over other people') showed a reliability of ~ = .65, ranging between 11 and 30 scale points (M = 20.36; SD = 4.98) scale points.

Data Reduction and Statistical Analyses Individual baseline cortisol levels were subtracted from cortisol peaks sampled 20 min

after the stress test for calculating response magnitudes. A two-way (time by day) within- subject ANOVA with repeated measurements on both factors was performed to test the effectiveness of the stressor on changes in cortisol levels through the stress protocol on each day. Student's t-tests were performed to test differences between baseline cortisol levels of day one through day five.

For further evaluation of the cortisol responses, areas under the curve of cortisol responses (AUC) were calculated for each of the five experimental days. Aggregation was employed by summation of single cortisol AUCs beginning with the second day. This procedure

Correlations between Cortisol Responses and Personality Traits 619

g

,.¢

<

500-

400-

300-

200 -

100-

0 - 1 1 T 1 r u

Day I Day 2 Day 3 Day 4 Day 5

Observa t ions

Fig. 1. Mean cortisol response (+ SE) to psychological stress as indexed by area under the response curve (AUC) on each of the five days; n = 20; units of value (y) axis are arbitrary.

resulted in aggregated AUCs of days two and three (AUC23), days two through four (AUC24), and days two through five (AUC25).

In order to investigate associations between endocrine data and psychological variables, Spearman rank correlations were computed between the mean aggregated cortisol AUC25 and all psychological variables. Further evaluation of these interactions was performed by correlating the single and aggregated cortisol AUCs with those psychological correlations that yielded significant results with the overall aggregated cortisol measure. In order to control effects of alpha error inflation, an adjusted level of significance was calculated according to Jacobs (1976).

The data on the habituation of the cortisol responses across the five days are published elsewhere (Kirschbaum et al., 1995). Also, the correlations between the mean aggregated cortisol AUC of days one to five (data not shown here) and the psychological variables are reported there.

RESULTS

Figure 1 shows AUC cortisol stress responses for all subjects on days one to five. The stress protocol induced a pronounced cortisol increase on all five days as indicated by the eortisol AUC on each day. Within-subject ANOVA showed a significant time effect on each day. Furthermore, within-subject ANOVA revealed a significant difference in cortisol responses across the five stress exposures. By contrasting day one versus days two to five, it

620 J .c . Pruessner et al.

Table I. df-, F- and p -va lues from A N O V A procedure of sal iva cort isol responses; n = 20

S o u r c e s o f v a r i a n c e df F - v a l u e p - v a l u e

Saliva cortisol samples 1-6; day 1 5 Saliva cortisol samples 1-6; day 2 5 Saliva cortisol samples 1-6; day 3 5 Saliva cortisol samples 1-6; day 4 5 Saliva cortisol samples 1-6; day 5 5 AUC cortisol responses day 1-5 4 Contrast of AUC cortisol response day 1 vs. day 2-5 1 AUC cortisol responses day 2-5 3

17.94 < .001 6.27 < .001 4.83 < .001 4.72 < .001 3.74 .004 5.19 .01

14.64 < .002 .64 n.s.

Table II. Corre la t ions be tween psycholog ica l var iables (explanat ion see text) and the mean cort isol stress (mean A U C ) response; n = 20

SKI INT POC FAT GI1 GI2 GI3 GI4 GI5 GI6

AUC - 0 . 6 9 0.01 - 0 . 2 1 0.51 - 0 . 6 9 0.56 0.44 0.12 0.63 0.11 25 p = .003 n.s. n.s. p < .05 p = .003 p = .02 n.s. n.s. p < .01 n.s.

Table III. S p e a r m a n - R a n k correla t ions be tween psycholog ica l var iables and single and aggrega ted cort isol stress responses

SC INT POC FAT G T I GT2 GT3 GT4 GT5 GT6

AUC1 - 0.50 0.13 -0 .10 0.23 -0 .41 0.10 0.09 -0 .03 0.28 -0 .03 AUC2 -0 .45 0.11 -0 .25 0.10 -0 .47 0.34 0.33 0.21 0.44 0.09 AUC3 - 0.58 0.09 -0 .19 0.33 - 0.52 0.24 0.17 0.23 0.30 0.22 AUC4 - 0 . 6 8 -0 .02 -0 .10 0.50 - 0 . 6 7 0 . 7 2 * 0.46 0.23 0 . 5 3 0.35 AUC5 -0 .32 -0.01 -0 .05 0.52 -0 .26 0.07 0.15 -0 .10 0.19 0.08 AUC23 - 0.61 0.12 -0 .07 0.25 - 0.57 0.36 0.18 0.11 0.42 0.07 AUC24 - 0 . 6 7 0.14 -0 .20 0 . 5 0 - 0 . 7 2 0 . 4 9 0.19 0.21 0.40 0.14 A U C 2 5 - 0 . 6 9 * 0 . 2 3 - 0 . 1 9 0 .51 - 0 . 7 0 * 0 . 5 6 0 .24 0 .25 0 . 6 3 0 . 3 4

AUC1, area under the curve of the cortisol stress response on day one; A U C 2 to AUC15 accordingly; for description of psychological variables refer to text; correlations shown bold are s ignif icant at zt = .05 s ignif icance level; correlations marked are s ignif icant at ~ = .003 s ignif icance level; n = 20.

was observed that stress exposure on day one was s ignif icant ly higher than those on days two to five. The mean cort isol response did not differ be tween days two to five indicat ing that the cort isol increase on these days was comparable . Table I shows the A N O V A results for the cort isol t ime effect wi th in each day and the contrasts be tween the cort isol stress response on day one versus the aggrega ted responses on days two to five as wel l as the main effect for the cort isol A U C s be tween the days two to five.

Correlations between Cortisol Responses and Personality Traits 62

| ,I

l''''l''''l'~''I '''I''''I''''I''''I''''

S1U 9!01.~.000 UOIlelgJJO 0

<

<

<

I

, , ~ , d , d ,

SlUO.IOI..J.J~O0 UO.qeJOJJO 0

r,..)

< ,_~

< ~

0

9 ~

. .

- ~ =

Z ~

II

o.)

622 J.c. Pruessner et al.

Computation of Spearman rank correlations indicated significant relationships of five of the psychological variables with the mean cortisol stress response at a significance level of 5%. With the number of correlations performed in this analysis, alpha adjustment according to Jacobs (1976) results in a significance level of a = .003. With this significance level, two of the 10 correlations performed in this analysis remain significantly correlated. Table II shows the correlation matrix between the psychological variables used in this study and the aggregated AUC cortisol response of days two to five.

For further evaluation, correlations were computed between single and aggregated cortisol AUCs and the psychological variables which were significantly correlated at the alpha level of ct = .05 with the overall cortisol stress response. Results of this analysis are shown in Table III.

As shown in Table III, increasing correlations between cortisol stress responses and the psychological variables were observed with data aggregation for those variables that were significantly correlated with the cortisol AUC of days two to five. As shown in Fig. 2, this pattern of increasing correlations was also observed for the other personality scales which were significantly correlated with the overall stress response.

DISCUSSION

The correlations found in this study suggest an association between certain psychological variables and cortisol responses after repeated exposures to psychosocial stress. After a single stress exposure, only one out of ten correlations between cortisol responses and personality variables was statistically significant without alpha-adjustment. This finding is in line with previous results from our laboratory (Kirschbaum et al., 1992) as well as from other research groups (e.g. Arnetz and Fjellner, 1986; van Eck et al., 1996). After repeated exposures, statistical significance with cortisol responses was discovered for two (third exposure), five (fourth exposure), and one (fifth exposure) out of ten personality variables, showing an inconclusive correlation pattern. After aggregation of the cortisol stress responses of days two to five, a consistent correlation pattern with increasing correlations of five questionnaire scales with the cortisol stress responses emerged.

The question arises why the procedure of data aggregation across multiple stress exposures was able to reveal a consistent correlation pattern with psychological variables while other procedures were not. There are at least three possible explanations for this: First, with this method of data analysis the effects of novelty as an important mediator for HPA axis activation have been controlled. On a first stress exposure, novelty might be the dominant situational characteristic which thus could mask effects of personality on the stress response. Although some authors have discussed interindividual differences in the perception of novelty (e.g. Zuckerman, 1990), it can be assumed that with repeated exposure to the same stressor, novelty becomes less dominant and other variables begin to exert stronger influences on the individual stress response.

Second, data aggregation might have led to the identification of a trait component of the state variable 'stress response'. There has been a considerable controversy about the usefulness and the restrictions of aggregation in the past (Allen and Potkay, 1983; Day et al., 1983; Endler, 1983; Epstein and O'Brien, 1985; Schroeder and Pendleton, 1983; Zuckerman, 1983). Epstein (1986) suggests that aggregation can be a useful tool if employed correctly, revealing general components of behavior observed and reducing situational influences. It is interesting to remark here, that for five out of ten psychological

Correlations between Cortisol Responses and Personality Traits 623

variables aggregation did not result in increasing correlations with the cortisol stress response. This suggests that data aggregation does not improve the odds for significant results in general. It rather appears to be a sensitive tool for identifying those personality factors which are associated with the individual stress response.

Third, differences in coping (Henry, 1992; Seligman, 1991; Ursin et al., 1978), might have resulted in different cortisol stress responses. However, it is unlikely that this was the sole factor responsible for the reported correlations. In this case, single stress responses should be significantly correlated with personality variables after repeated exposure. However, only with aggregated stress responses significant correlations were observed.

Further studies are necessary to validate the correlations of the questionnaire scales with the cortisol stress responses. No correlations with other questionnare data for cross- validation were available. Also, no state measures or interview data had been collected. The scales found here to correlate with cortisol stress responses show similarities with those variables identified by others to modulate the perception and the response to a psychological threat. Self-concept, as well as locus of control have been identified to be possible mediators of the stress response in the past (Koohlhaas and Bohus, 1989; Seligman, 1991; Seeman et al., 1995; Zorrilla et al., 1995). Some of the questionnaire scales of the Giessen-Test refer to defense mechanisms that have been found to be associated with cortisol stress responses (e.g. Vaernes et al., 1982). Overall, the image of a subdominant, externally controlled, and insecure person showing greater cortisol stress responses appears.

A final call for cautious interpretation of the data refers to the small sample size and the highly selected group examined. Only healthy, nonsmoking, male students with a narrow age range were studied. Further investigations will be necessary to validate and extend these associations and the usefulness of data aggregation in detecting personality trait-related cortisol stress response dispositions. We suggest that repeated stress exposure in combination with data aggregation might prove a powerful tool for the investigation of cross-situational response dispositions in psychobiological research.

REFERENCES

Allen, B. P. and Potkay, C. R. (1983) As arbitrary as ever: Comments on Zuckerman's rejoinder. Journal of Personality and Social Psychology 44, 1087-1089.

Arnetz, B. B. and Fjellner, B. (1986) Psychological predictors of neuroendocrine responses to mental stress. Journal of Psychosomatic Research 30, 297-305.

Beckmann, D., Br~ihler, E. and Richter, H. E. (1991)Der Giessen-Test (GT). Ein Test fiir Individual- und Gruppendiagnostik. Hans Huber, Bern.

Blood, G. W., Blood, I. M., Bennett, S., Simpson, K. C., Susman, E. J. and Miller, A. H. (1994) Subjective anxiety measurements and cortisol responses in adults who stutter. Journal of Speech and Hearing Research 37, 760-768.

Bohnen, N., Nicolson, N., Sulon, J. and Jolles, J. (1991) Coping style, trait anxiety and cortisol reactivity during mental stress. Journal of Psychosomatic Research 35(2/3), 141-147.

Day, H. D., Marshall, D., Hamilton, B. and Christy, J. A. (1983) Some cautionary notes regarding the use of aggregated scores as a measure of behavioral stability. Journal of Research in Personality 17, 97-109.

Dess, N. K., Linwick, D., Patterson, J., Overmier, J. B. and Levine, S. (1983) Immediate and proactive effects of controllability and predictability on plasma cortisol responses to shocks in dogs. Behavioral Neuroscience 97, 1005-1016.

Dressend6rfer, R. A., Kirschbaum, C., Rohde, W., Stahl, F. and Strasburger, C. J. (1992) Synthesis of a cortisol-biotin conjugate and evaluation as a tracer in an immunoassay for salivary cortisol measurement. Journal of Steroid Biochemistry and Molecular Biology 43(7), 683--692.

624 J.C. Pruessner et al.

Endler, N. (1983) Interactionism: A personality model but not yet a theory. In PersonalityICurrent Theory and Research, ed. M. M. Page, pp. 155-200. University of Nebraska Press, Lincoln.

Epstein, S. (1986) Does aggregation produce spuriously high estimates of behavior stability? Journal of Personality and Social Psychology 50(6), 1199-1210.

Epstein, S. and O'Brien, E. J. (1985) The person-situational debate in historical and current perspective. Psychological Bulletin 98(3), 513-537.

Grandin, T. (1997) Assessment of stress during handling and transport. Journal of Animal Sciences 75, 249-257.

Gross, M. J., Kahn, J. P., Laxenaire, M., Nicolas, J. P. and Burlet, C. (1994) Corticotropin-releasing factor and anorexia nervosa: reactions of the hypothalamus-pituitary-adrenal axis to neurotropic stress. Annuals of Endocrinology 55, 221-228.

Gunnar, M. R., Connors, J. and Isensee, J. (1989) Lack of stability in neonatal adrenocortical reactivity because of rapid habituation of the adrenocortical response. Developmental Psycho- biology 22, 221-233.

Gunnar, M. R., Hertsgaard, L., Larson, M. and Rigatuso, J. (1991) Cortisol and behavioral responses to repeated stressors in the human newborn. Developmental Psychobiology 24, 487-505.

Hennessy, M. B. and Kaplan, J. N. (1982) Influence of the maternal surrogate on pituitary-adrenal activity and behavior of infant squirrel monkeys. Developmental Psychobiology 15, 423-431.

Hennessy, M. B., Mendoza, S. P., Mason, A. W. and Moberg, G. P. (1995) Endocrine sensitivity to novelty in squirrel monkeys and titi monkeys: species differences in characteristic modes of responding to the environment. Physiology and Behavior 57, 331-338.

Henry, J. P. (1992) Biological basis of the stress response. Integrative Physiological and Behavioral Science 27(1), 66-83.

Houtman, I. L.D. and Bakker, F. C. (1991) Individual differences in reactivity and coping with the stress of lecturing. Journal of Psychosomatic Research 35, 11-24.

Hubert, W. and de Jong-Meyer, R. (1992) Saliva cortisol responses to unpleasant film stimuli differ between high and low trait anxious subjects. Neuropsychology 25, 115-120.

Hubert, W., Moiler, M. and Nieschlag, E. (1989) Stress reactions in response to the procedure of LHRH tests as measured by salivary and serum cortisol and psychological variables. Hormonal Research 32, 198-202.

Hyyppa, M. T. (1987) Psychoendocrine aspects of coping with distress. Annuals" of Clinical Research 19(2), 78-82.

Jacobs, K. W. (1976) A table for the determination of experimenterwise error rate (alpha) from independent comparisons. Educational and Psychological Measurement 36, 899-903.

Kirschbaum, C., Bartussek, D. and Strasburger, C. J. (1992) Cortisol responses to psychological stress and correlations with personality traits. Personality and Individual Differences 13(12), 1353-1357.

Kirschbaum, C., Pirke, K. M. and Hellhammer, D. H. (1993) The 'Trier Social Stress Tes t ' - - a tool for investigating psychobiological stress responses in a laboratory setting. Neuropsychobiology 28, 76- 81.

Kirschbaum, C., Pruessner, J. C., Stone, A. A., Federonko, I., Gaab, J., Lintz, D., Schommer, N. and Hellhammer, D. H. (1995) Persistent high cortisol responses to repeated psychological stress in a subpopulation of healthy men. Psychosomatic Medicine 57, 468-474.

Koohlhaas, J. and Bohus, B. (1989) Social control in relation to neuroendocrine and immunological responses. In Stress, Personal Control and Health, eds. A. Steptoe and A. Appels, pp. 231-256. Wiley, New York.

Krampen, G. (1991) Fragebogen zur Kompetenz- und Kontrolliiberzeugung. Hogrefe, G6ttingen. Lehmann, J., Tennigkeit, M., Haschke, R., Haschke, W. and Rosahl, S. (1992) Differences in mental

task performance and slow potential shifts in subjects differing in cortisol level. International Journal of Psychophysiology 13, 1-8.

Mason, J. W. (1968) A review of psychoendocrine research on the pituitary-adrenal cortical system. Psychosomatic Medicine 30(Suppl), 576-607.

Oitzl, M. S., van Haarst, A. D., Sutanto, W. and de Kloet, E. R. (1995) Corticosterone, brain mineraloeorticoid receptors (MRs) and the activity of the hypothalamic-pituitary-adrenal (HPA) axis: the Lewis rat as an example of increased central MR capacity and a hyporesponsive HPA axis. Psychoneuroendocrinology 20, 655-675.

Salmon, P., Pearce, S., Smith, C. C.T. and Manyande, A. (1989) Anxiety, type a personality and endocrine responses to surgery. British Journal of Clinical Psychology 28, 279-280.

Correlations between Cortisol Responses and Personality Traits 625

Schroeder, D. J. and Pendleton, M. G. (1983) The adjective generation technique: Consistency of self- description in psychiatric patients. Journal of Personality 51, 631-639.

Seeman, T. E., Berkman, L. F., Gulanski, B. I., Robbins, R. J., Greenspan, S. L., Charpentier, P. A. and Rowe, J. W. (1995) Self-esteem and neuroendocrine response to challenge: MacArthur studies of successful aging. Journal of Psychosomatic Research 39(1), 69-84.

Seligman, M. E. P. (1991) Learned Optimism. Knopf, New York. Selye, H. (1936) A syndrome produced by diverse noxious agents. Nature 138, 32-36. Ursin, H., Baade, E. and Levine, S. (1978) Psychobiology of Stress----a Study of Coping Men.

Academic Press, New York. Ursin, H. and Olff, M. (1993) Psychobiology of coping and defence strategies. NeuropL~vchobiolog 3'

28, 66-71. Vaernes, R., Ursin, H., Darragh, A. and Lambe, R. (1982) Endocrine reponse patterns and

psychological correlates. Journal of Psychosomatic Research 26(2), 123-131. Van Cauter, E. (1987) Pulsatile ACTH secretion. In Episodic Hormone Secretion: From Basic Science

to Clinical Application, eds. T. Wagner and M. Filicori, pp. 65-75. TM, Hameln. van Eck, M., Berkhof, H., Nicolson, N. and Sulon, J. (1996) The effects of perceived stress, traits,

mood states, and stressful daily events on salivary cortisol. Psychosomatic Medicine 58, 432-446. Visintainer, M. A., Volpicelli, J. R. and Seligman, M. E. (1982) Tumor rejection in rats after

inescapable or escapable shock. Science 216, 437-439. Voigt, K., Ziegler, M., Grunert-Fuchs, M., Bickel, U. and Fehm-Wolfsdorf, G. (1990) Hormonal

responses to exhausting physical exercise: the role of predictability and controllability of the situation. Psychoneuroendocrinology 15, 173-184.

Weinberg, J. and Wong, R. (1986) Adrenocortical responsiveness to novelty in the hamster..lournal of Physiology and Behavior 37, 669-672.

Weizman, R., GiI-Ad, I., Karp, L., Laor, N., Barber, Y. and Rehavi, M. (1992) Platelet imipramine binding and plasma cortisol levels in Israeli civilians during the Gulf War. Biological P~sychiatry 32, 170-178.

Yehuda, R., Giiler, E. L. and Mason, J. W. (1993) Psychoneuroendocrine assessment of posttraumatic stress disorder: Current progress and new directions. Progress in Neuropsychopharmacology and Biological Psychiatry 17, 541-550.

Zorrilla, E. P., DeRubeis, R. J. and Redei, E. (1995) High self-esteem, hardiness and affective stability are associated with higher basal pituitary-adrenal hormone levels. Psychoneuroendocrinology 20(6), 591-601.

Zuckerman, M. (1983) The distinction between trait and state scales is not arbitrary: Comment on Allen and Potkay's 'On the arbitrary distinction between traits and states'. Journal of Personality and Social Psychology 44, 1083-1086.

Zuckerman, M. (1990) The psychophysiology of sensation seeking. Journal of Personality 58(1), 313-345.