Individual differences in children's cortisol response to the beginning of a new school year

Psychoneuroendocrinology 27 (2002) 635–650www.elsevier.com/locate/psyneuen

Individual differences in children’s cortisolresponse to the beginning of a new school year

Jacqueline Bruce*, Elysia Poggi Davis, Megan R. GunnarInstitute of Child Development, 51 East River Road, University of Minnesota, Minneapolis, MN 55455,

USA

Received 31 October 2000; received in revised form 6 June 2001; accepted 6 June 2001

Abstract

The relationship between salivary cortisol levels at the beginning of the school year andparent reports of temperament using the Children’s Behavior Questionnaire (CBQ) were inves-tigated in 35 first graders. Cortisol was sampled in the morning, afternoon, and evening onthe first and fifth days of school and two weekend days later in the school year. On the firstday of school compared to weekend days, children displayed a steeper cortisol slope acrossthe day due to lower afternoon and evening levels. By the fifth day of school, cortisol levels,on average, were not different than on weekend days. However, using change scores to reflectthe response to school days relative to weekend days, children who scored higher in Surgency(i.e., enjoyment of intense play, high activity level, impulsivity, lack of shyness) continued todisplay a steeper cortisol slope on the fifth day of school with higher morning and lowerevening cortisol levels. In contrast, shyness, which negatively contributes to Surgency, waspositively correlated with evening change scores on the fifth day of school. 2002 ElsevierScience Ltd. All rights reserved.

Keywords: Children; Normative challenge; Cortisol; Temperament; Surgency; Shyness

1. Introduction

Children differ in their response to novel situations. While some children approachnovel situations with interest and excitement, other children hesitate and appear to

* Corresponding author. Tel.:+1-612-626-8949; fax:+1-612-624-6373.E-mail address: [email protected] (J. Bruce).

0306-4530/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0306 -4530(01 )00031-2

636 J. Bruce et al. / Psychoneuroendocrinology 27 (2002) 635–650

find these situations threatening and scary. These individual differences are oftenascribed to temperament, which has been viewed as constitutionally-based individualdifferences in reactivity and regulation (Rothbart and Bates, 1998). It is expectedthat novel situations may be stressful for shy, inhibited children and may stimulateneural systems that increase levels of neuroendocrine stress hormones (Kagan etal., 1987). However, neuroendocrine responses vary across individuals and acrosssituations for an individual (Lazarus and Launier, 1978; Nicolson, 1992). Thus, therelationship between neuroendocrine responses and temperament may depend uponthe challenge studied. In the following study, we used the beginning of a new schoolyear as a normative challenge (Boyce et al., 1995). We were interested whether thechallenge of entering first grade would stimulate an increase in cortisol, a hormonalend-product of the hypothalamic–pituitary–adrenocortical (HPA) system. Given thenature of the challenge (i.e., the school day extends over many hours), cortisolsamples were collected in the morning, afternoon, and evening to determine theimpact of this challenge on the daily pattern of cortisol production. We also examinedthe relationship between the children’s cortisol response to the new school year andtemperament as reported by their parents.

Cortisol, a hormone produced by the HPA system, has traditionally been the focusof research on stress physiology (Hennessy and Levine, 1979; Mason, 1975; Rose,1980). Research with adults and children has demonstrated that cortisol levels tendto elevate in response to situations that involve novelty, uncontrollability, or threat(Hennessy and Levine, 1979; Kirschbaum and Hellhammer, 1994). Activation of theHPA system to psychological stressors also involves activity of the central nucleusof the amygdala and bed nucleus of the stria terminalis (Rosen and Schulkin, 1998). Itis believed that the activation of the HPA system mobilizes the central and peripheralresources necessary to manage challenge (de Kloet, 1991). Although the activity ofthe HPA system is necessary for survival, chronic elevations in cortisol appear tohave a deleterious effect upon immune functioning (Cacioppo, 1994; Coe et al.,1988) and memory and attentional processes (Born et al., 1987; Kruesi et al., 1989;Lupien et al., 1994). Furthermore, it has been proposed that chronic elevations incortisol increase the activity of brain regions involved in fear (i.e., the amygdala andthe bed nucleus of the stria terminalis) and play a role in the development of patho-logical anxiety (Rosen and Schulkin, 1998; Schulkin et al., 1998). Thus, it has beenargued that the activity of the HPA system must be well regulated with an adequatecortisol response to cope with challenge and an efficient termination of the responseto avoid the negative consequences related to chronic elevations in cortisol (de Kloet,1991; Gunnar et al., 1997; Munck et al., 1984).

Shyness or behavioral inhibition has been a temperament characteristic of parti-cular interest for researchers in child development. It is believed that extreme shynessin childhood is associated with an increased risk for anxiety disorders, such as panicdisorder and social phobia, in adulthood (Rosenbaum et al., 1991). In addition, shy-ness is believed to reflect an individual difference in a lowered threshold for physio-logical and behavioral reactivity (Kagan et al., 1988a). Although it is expected thatshyness would be associated with a greater cortisol response to novel or unfamiliarevents, studies examining this relationship have yielded mixed results. In one study,

637J. Bruce et al. / Psychoneuroendocrinology 27 (2002) 635–650

a group of extremely inhibited 5-year-olds displayed higher baseline cortisol levelsin the morning and higher cortisol levels following a series of challenging events ina laboratory session as compared to extremely uninhibited children (Kagan et al.,1987). However, two years later, cortisol levels did not differentiate these two groupsof children (Kagan et al., 1988b). Schmidt et al. (1997) have found that extremelyinhibited preschool-aged children had higher morning cortisol levels, but did nothave significantly higher cortisol levels during a laboratory session. Additionally, ina study with typically developing toddlers, higher mid-morning cortisol levels athome were associated with teacher reports of anxious, shy behaviors (de Haan etal., 1998). However, this association between cortisol levels and shyness was notsignificant when the children were assessed in preschool (Gunnar et al., 1997). Thus,the relationship between cortisol levels and shyness has been found to be inconsist-ent, and possibly context dependent.

In fact, a number of studies have demonstrated that children who are high insurgency or extroversion, and thus low in shyness, display higher cortisol levels inresponse to new social situations, such as entry into a new peer group. The tempera-ment dimension of Surgency reflects the enjoyment of intense play (i.e., going downhigh slides or riding a bicycle really fast), high activity level, impulsivity, and lackof shyness. Gunnar et al. (1997) found that children who displayed high cortisolreactivity during the first month of nursery school, but low cortisol reactivity in themiddle of the school year, were rated as more extroverted and socially competentby their teachers. In a sample of elementary school children between the ages of 7and 12, Davis et al. (1999) found that parent reports of Surgency, rather than shyness,were associated with greater elevations in noon and evening cortisol levels on thefifth, but not the first, day of school. Among adults, surgency has not been studiedwith regard to cortisol response to new social situations; however, dominance hasbeen examined. Assuming that dominant individuals are unlikely to be shy and soci-ally inhibited, the studies of group formation with adults are consistent with thestudies conducted with children. In one study of army recruits, Hellhammer et al.(1997) reported that individuals who were identified as socially dominant displayedmore marked elevations in cortisol in response to social and physical challengesduring boot camp than did subordinate individuals who displayed a blunted cortisolresponse. Taken in combination, these results suggest that moderate elevations incortisol in response to new social situations are not associated with shyness orbehavioral inhibition. Instead, surgency and social dominance appear to predict elev-ations in cortisol in response to new social situations. However, surgency and domi-nance are complex constructs, and the processes that may be operating to producelarger elevations in cortisol in response to new social situations are unclear.

The purpose of this study was to replicate and extend the findings of Davis et al.(1999) by investigating the relationship between children’s cortisol response to thebeginning of a new school year and individual differences in temperament, parti-cularly Surgency and shyness. In this study, we selected a sample of children enteringthe first grade, rather than the more heterogeneous age group utilized in the studyby Davis et al. (1999). It was believed that the children’s lack of experience withschool might influence the likelihood of displaying a cortisol response to the begin-


ning of the school year. As in the previous study by Davis et al. (1999), salivarycortisol was measured on the first and fifth day of the new school year and on twoweekend days at least one month after the start of the school year. Parents completedthe Children’s Behavior Questionnaire (CBQ), a questionnaire that assesses 15 indi-vidual subscales and 3 higher-order temperament dimensions of Surgency, NegativeAffectivity, and Effortful Control (Ahadi et al., 1993; Rothbart et al., 2001). Shyness,which is a subscale on the CBQ that contributes negatively to the temperamentdimension of Surgency, was also analyzed separately since it has traditionally beenof particular interest in understanding individual differences in cortisol reactivity.However, based on previous research (Davis et al., 1999), we expected that Surgency,rather than shyness, would be associated with greater elevations in cortisol inresponse to the beginning of a new school year.

In addition, we were interested in providing a finer analysis of the relationshipbetween Surgency and cortisol reactivity by examining aspects of the children’s func-tioning that are presumably encompassed in the construct of surgency. For example,impulsivity is one of the subscales that contribute to Surgency on the CBQ. Onepossible explanation of the relationship between Surgency and greater increases incortisol in a new social situation is that impulsive children may rush into new andexciting situations and may violate classroom rules, such as talking to other studentsduring class and not listening to the teacher (Gunnar, 1994). This approach to newsocial situations may create conflicts and stressors that are not encountered by lessimpulsive children. Therefore, Surgency may reflect the children’s difficultyinhibiting or regulating their behavior. In fact, previous research with the childrenin the present study found an association between Surgency and poor inhibitorycontrol (Davis et al., 2001). In that study which investigated the relationship betweenthe anterior attentional system (Posner and Rothbart, 1994) and different aspects ofinhibitory control, Surgency was associated with poor performance on tasks that havebeen found involve the anterior attentional system in neuroimaging studies (Caseyet al., 1997). In addition, children who scored higher in Surgency were rated asexhibiting more externalizing behaviors, such disobeying rules and fighting withothers, by their parents. This association between Surgency and externalizingbehaviors was of particular interest since the children were not within the clinicalrange for behavior problems. Given these associations between Surgency and poorself-regulation, we were interested in examining the relationship between the chil-dren’s cortisol response to the beginning of the school year and parent reports ofexternalizing behaviors. If elevations in cortisol are related to behavior problems,the association between Surgency and cortisol reactivity may reflect the children’sdifficulty regulating their behavior and complying with classroom rules.

2. Method

2.1. Participants

Thirty-four children (20 girls) were retained from a sample of 61 children whoparticipated in a study two to nine months earlier (Davis et al., 2001). All of the


children were entering the first grade (M age=81.32 months, SD=2.18 months, agerange=76 to 85 months). One family could not be contacted, 10 families did notagree to participate, and 12 families agreed to participate but did not complete thesampling procedure. Several children were excluded because they were not attendingschool (n=2), were using an asthma inhaler (n=1), or had been diagnosed with aclinical disorder (n=1). The children who participated in the study did not signifi-cantly differ from the children who did not participate on the three temperamentdimensions, Hotellings F(3,53)=0.51, ns, parent reports of behavior problems,F(1,56)=0.06, ns, or the cortisol measures collected during the laboratory session,F(1,55)=1.72, ns, or at home, F(1,50)=2.17, ns.

2.2. Procedure

Families were asked to participate in a laboratory session that lasted approximatelyone hour. While the children completed several inhibitory control tasks, their parentscompleted the CBQ (Ahadi et al., 1993; Rothbart et al., 2001) and a social skillsquestionnaire (Gresham and Elliot, 1990). Several months later, parents were askedto collect saliva samples from their children on two school days at the beginning ofthe school year and on two weekend days. Parents completed the CBQ and a diaryfor each sampling day noting the child’s general health, the use of medication, thetime of meals, and sampling times. Parents also completed the Life Events Question-naire (modified from Sarason et al., 1979) in order to provide information aboutmajor life events that the children experienced within the last 12 months. The meannumber of life events for this sample (M=2.31 events, SD=1.68 events) suggests thatthe children were not experiencing a number of major life events in addition tobeginning a new school year. Analyses of the individual events assessed by thequestionnaire also revealed that none of the children experienced a serious illnessor injury, divorce or separation of parents, or death in the immediate family withinthe 12 months prior to beginning a new school year.

2.3. Measures

2.3.1. Salivary cortisolFamilies agreeing to participate in the study were mailed saliva collection kits.

To collect saliva, the children chewed a piece of Trident Original sugarless gumto stimulate salivation. The use of Trident Original sugarless gum has been shownto have little effect on cortisol levels (Schwartz et al., 1998). The children then useda plastic straw to expel the saliva into a small plastic vial. The parents were askedto collect saliva samples from their child in the morning (30 minutes after the childawoke, but before breakfast), at 1600 h, and in the evening (within 30 minutes ofbedtime). In the previous study examining children’s response to a new school year(Davis et al., 1999), the children collected the second saliva sample at noon. How-ever, it was found that only 63% of the first graders collected noon saliva sampleson the first and fifth days of school. Since the sample for the present study wasexclusively comprised of children entering first grade, it was decided that the parents


should collect the second sample after the children returned from school. Consistentwith the previous study (Davis et al., 1999), parents were instructed to sample onthe first and fifth days of school and two weekend days at least one month after thebeginning of the school year. Parents stored the saliva samples in the refrigeratoruntil all of the samples had been collected and then mailed the samples to the labora-tory where they were stored in a freezer at �20°C until assayed. Research (Clementsand Parker, 1998) suggests that conditions experienced during mailing should notinfluence cortisol concentrations in saliva. Saliva samples were assayed for cortisoldetermination using the CIBA Magic RIA (Kirschbaum et al., 1989). All of thesamples from a child were included in the same assay batch to eliminate withinsubject inter-assay variance. All of the samples were assayed in duplicated and aver-aged. Duplicates varying by more than 20% were re-assayed. The inter-assay andintra-assay coefficients of variance were 16.69 and 7.40, respectively.

Previous research has demonstrated that cortisol levels are affected by generalhealth, food intake, and sleep patterns (de Kloet, 1991). Therefore, the diary com-pleted by the parents was inspected to ensure sampling guidelines were followed(e.g. samples were collected before meals) and the children were generally healthyon the sampling days. Cortisol values that were more than three standard deviationsabove the mean, and thus may have been sampled without adherence to the guide-lines, were removed from analyses. This resulted in the removal of one morningsample from the first day of school, three afternoon samples from the weekend days,and two evening samples from the weekend days. The other samples from thesechildren remained in the analyses. The cortisol values were log transformed to nor-malize the distribution.

The cortisol values from the two weekend days were averaged to create a morning,afternoon, and evening weekend cortisol value. Since cortisol levels on the fifth, butnot the first, day of school, were associated with parent reports of temperament inprevious research (Davis et al., 1999), the cortisol values from the first and fifth dayof school were analyzed separately. To reduce the number of analyses, a slope meas-ure was created for the first day of school, the fifth day of school, and the weekenddays reflecting the change in cortisol across the day. Cortisol values were regressedon the sampling times, and the resulting slope value was retained. The cortisol slopemeasure was reverse-scored so that larger values reflect sharper decreases in cortisollevels across the day from morning to evening.

Descriptive information about the sampling times is shown in Table 1. Consistentwith previous research (Davis et al., 1999), the morning samples collected on theschool days were earlier than on the weekend days. Given the circadian rhythm inthe production of cortisol (Kirschbaum and Hellhammer, 1989), the difference insampling times could result in higher morning cortisol values on the school days.This fact was taken into account in interpretation of the cortisol data.

2.3.2. TemperamentAt the laboratory session and at the beginning of the school year, the children’s

parents completed the CBQ, a measure designed to assess temperament for childrenbetween the ages of three and eight (Ahadi et al., 1993; Rothbart et al., 2001). The


Table 1Descriptive statistics for time of saliva sampling

First day of school Fifth day of school Weekends days

SamplingM SD n M SD n M SD n

times

Morning 0728 h 31 min 31 0730 h 37 min 34 0819 h 47 min 33Afternoon 1639 h 46 min 34 1626 h 41 min 32 1620 h 37 min 32Evening 2018 h 37 min 34 2021 h 41 min 31 2035 h 49 min 32

CBQ is a 195-item questionnaire that provides scores for 15 subscales and 3 higher-order dimensions. The higher-order dimensions are Surgency, Negative Affectivity,and Effortful Control. The subscales included in each of the higher-order dimensionsare listed, followed by the Cronbach alpha for the scale. Surgency was computed asthe average of the standardized scores for the subscales of activity level (alpha=0.73),high pleasure (alpha=0.78), impulsivity (alpha=0.83), and shyness, reversed scored(alpha=0.93). Negative Affectivity was computed as the average of the standardizedscores for the subscales of anger (alpha=0.78), discomfort (alpha=0.71), fear(alpha=0.73), sadness (alpha=0.65), and soothability, reversed scored (alpha=0.77).Finally, Effortful Control was computed as the average of the standardized scoresfor the subscales of attention focusing (alpha=0.73), inhibitory control (alpha=0.84),low intensity pleasure (alpha=0.71), perceptual sensitivity (alpha=0.82), andsmiling/laughter (alpha=0.84). Since the test–retest reliability coefficients for thesubscales were moderately high (rs ranged from 0.62 to 0.86, Ps�0.01), the subs-cales and the higher-order dimensions assessed at the laboratory session and at thebeginning of the school year were averaged.

2.3.3. Behavior problemsAt the laboratory session, the parents completed the Social Skills Rating System

(SSRS; Gresham and Elliot, 1990), a questionnaire assessing social competence andbehavior problems for children in elementary school. The questionnaire yields asummary measure of Problem Behaviors that reflects problematic behaviors, such asexternalizing behaviors, internalizing behaviors, and hyperactivity. The mean scorefor Problem Behaviors in this sample was 11.58 for girls and 12.85 for boys, whichwas comparable to the means reported by Gresham and Elliot (1990) from theirnational standardization sample (10.9 and 13.8 respectively). Additionally, none ofthe children in the present study were within the clinical range for behavior problems.Since we were primarily interested in externalizing behavior problems for this study,we removed items reflecting internalizing behaviors from the Problem Behaviorsmeasure. Parents were not asked to complete the SRSS at the beginning of the schoolyear. However, Gresham and Elliot (1990) reported that the SRSS demonstrates mod-erately high test–retest reliability for the scales assessing externalizing behaviors andhyperactivity (rs were 0.72 to 0.58 respectively).


2.4. Analysis plan

First, the cortisol slope measures on the first day and fifth day of school werecompared to the weekend days using an ANOVA with repeated measures and Bon-ferroni corrected post hoc tests. Significant differences were further analyzed byexamining the morning, afternoon, and evening cortisol levels. In order to exploreindividual differences in the cortisol response, change scores were computed for thecortisol slope measures and the individual cortisol levels. The children’s cortisolmeasures from the weekend days were subtracted from their cortisol measures onthe first and the fifth day of school. The association between the cortisol changemeasures and temperament was investigated using Pearson product correlations.Finally, the relationship between the cortisol change measures and parent reports ofbehavior problems was investigated.

3. Results

3.1. Salivary cortisol

Descriptive data for the cortisol measures are shown in Table 2. To examine theeffect of sex and day on cortisol slope, a 2×3 (Sex×Sampling Day) ANOVA withrepeated measures on the last factor was computed using Greenhouse–Geisser adjust-ments as required. The main effect of sex was not significant, F(1,28)=0.08, ns.However, the effect of day was significant, F(1.46,40.75)=7.68, P=0.004. Using Bon-ferroni corrected post hoc tests, cortisol slope was significantly steeper on the firstday of school than on the weekend days, t(31)=3.88, P=0.003. Further analyses indi-cated that the afternoon, t(31)=�3.74, P=0.001, and evening, t(31)=�4.06, P=0.001,cortisol levels were significantly lower on the first day of school than on the weekenddays. In addition, there was a non-significant trend for morning cortisol levels,t(29)=1.92, P=0.065. The cortisol slope on the fifth day of school was not signifi-cantly different from the slope on the first day of school, t(31)=1.69, ns, or theweekend days, t(29)=1.67, ns.

Although the morning cortisol levels were not significantly higher on the first dayof school compared to the weekend days, this undoubtedly contributed to the differ-

Table 2Descriptive statistics for cortisol values in µg/dl

First Day of School Fifth Day of School Weekends Days

Cortisol measures M SD M SD M SD

Morning 0.71 0.38 0.63 0.26 0.59 0.19Afternoon 0.14 0.07 0.19 0.08 0.21 0.08Evening 0.05 0.05 0.06 0.04 0.09 0.05


ence in the cortisol slope measure on first day of school. As shown in Table 1, themorning cortisol samples on the school days were obtained approximately 50 minutesearlier than on weekend days. Thus, we were concerned that the difference betweenthe sampling times may have influenced cortisol levels. To determine the impact ofthe difference in morning sampling times, a time-difference score was calculatedbetween the first day of school and the weekend days and was correlated with thecortisol change scores for the first day of school. If the increase in slope and morningcortisol levels on the first day of school was due merely to the difference in morningsampling times, then the children with larger time-difference scores should also havelarger cortisol change scores. The results showed that the time-difference scores werenot significantly correlated with the change in cortisol slope, r(29)=�0.25, ns, ormorning cortisol levels, r(30)=0.10, ns, for the first day of school. These results, inaddition to the significant effect for the afternoon and evening cortisol levels, werereassuring that the steeper cortisol slope on the first day of school was not an artifactof the difference in the morning sampling times.

3.2. Associations between salivary cortisol and temperament

In order to explore individual differences in the children’s response to the begin-ning of the school year, change scores for the cortisol slope measure and the individ-ual levels were computed by subtracting the weekend cortisol measures from themeasures on the first and fifth days of school. The correlations between change incortisol slope for the first and fifth day of school and the temperament dimensionsof Surgency, Effortful Control, and Negative Affectivity can be seen in Table 3.Surgency was positively correlated with the change in cortisol slope for the fifth dayof school. These results indicate that the children who scored higher in Surgencydisplayed a steeper change in cortisol across the day on the fifth day of school relativeto the weekend days. When the subscales contributing to Surgency were examined(see Table 3), it was noted that the relationship between high pleasure and the changein cortisol slope for the fifth day of school was particularly strong. By examiningthe correlations between Surgency and the cortisol change scores for the morning,afternoon, and evening on the fifth day, it was found that Surgency was associated

Table 3Correlations between change in cortisol slope and temperament

First day of school df=32 Fifth day of school df=30a

Effortful Control �0.06 0.09Negative Affectivity 0.22 �0.24Surgency: 0.01 0.38*activity level �0.01 0.08high pleasure �0.01 0.49**impulsivity �0.01 0.31shyness �0.07 �0.30

a **P�0.01. *P�0.05.


with higher morning cortisol levels, r(33)=0.37, P=0.036, and lower evening cortisollevels, r(28)=�0.42, P=0.025, on the fifth day relative to the weekend days. Further-more, Surgency and the cortisol slope measure, r(32)=0.43, P=0.013, and cortisollevels in the morning, r(34)=0.41, P=0.017, and evening, r(30)=�0.37, P=0.045, onthe fifth day of school, but not the weekend days (rs ranged from �0.22 to 0.19, ns),were significantly correlated. These findings suggest that the associations betweenSurgency and the cortisol change measures reflect individual differences in the chil-dren’s response to the fifth day of school as opposed to differences in their baselinecortisol levels. None of the three higher-order temperament dimensions were signifi-cantly correlated with the cortisol change measures for the first day of school, andEffortful Control and Negative Affectivity were not significantly associated withcortisol change measures for the fifth day of school.

Because shyness, which loads negatively on the Surgency dimension, was of parti-cular interest, the relationship between shyness and cortisol change measures wasalso examined. Parent reports of shyness and change in cortisol slope for the firstand fifth day of school were not significantly correlated. However, an examinationof the morning, afternoon, and evening change scores revealed that shyness wassignificantly correlated with the evening change scores for the fifth day of school,r(28)=0.50, P=0.01. Because shyness and the evening cortisol levels on the weekenddays were significantly correlated, r(32)=�0.39, P=0.027, the association betweenevening cortisol levels on the fifth day of school and shyness was recomputed usinga partial correlation to control for the weekend association. The results showed thatshyness was significantly correlated with evening cortisol levels on the fifth day ofschool even after controlling for the weekend association, partial r(25)=0.44,P=0.020. Shyness was not correlated with the morning or afternoon change scoreson either school day (rs ranged from �0.18 to 0.15, ns).

3.3. Associations between salivary cortisol and behavior problems

The relationship between cortisol change measures and externalizing behaviorswas then examined. Parent reports of Problem Behaviors were not significantly corre-lated with the cortisol change measures for the first or fifth day of school (rs rangedfrom �0.18 to 0.20, ns).1

4. Discussion

The beginning of a new school year is a challenge that most children encounter,and many children demonstrate a physiological response to this challenge. In the

1 In the laboratory session, the children completed two computerized inhibitory control tasks developedby Casey et al. (1997). Salivary cortisol was also collected during the laboratory session and at home ontwo school days after the session. Accuracy on the tasks was associated with higher average cortisollevels in the laboratory and at home (Davis et al., 2001). Consistent with these findings, accuracy on theinhibitory control tasks was related to higher average cortisol level on the weekend days, r(31)=0.37,P=0.038, despite being collected two to nine months later. However, accuracy was not associated withthe children’s cortisol levels on the first, r(31)=0.09, ns, or fifth day of school, r(31)=0.01, ns.


present study, a greater change in cortisol levels across the day was observed on thefirst day of school as compared to the weekend days. In addition, some childrencontinued to demonstrate a more marked cortisol slope on the fifth day of school.The change in slope on the first day of school reflected a non-significant trend forhigher than baseline cortisol levels in the morning and significantly lower than base-line cortisol levels in the afternoon and evening. This finding extends the results ofthe previous research, which reported that on both the first and fifth days of school,nearly 40% of the children displayed significantly higher cortisol levels during themiddle of the school day (Davis et al., 1999). Furthermore, it was noted that theyounger children in that study were more likely to experience an elevation in theirnoon cortisol levels during the first days of school. Taken together, these studiessuggest that for some children, particularly younger children, the HPA systemresponds to the challenge of the first days of a new school year.

By the fifth day of school, on average, the children did not display a significantdifference in their change in cortisol levels across the school day as compared toweekend days. However, consistent with previous research (Davis et al., 1999), cor-tisol activity on the fifth day of school, but not the first day of school, was predictedby individual differences in temperament. Although it may be counterintuitive thattemperament characteristics would be more strongly associated with cortisolresponses upon repeated exposure to the school setting, similar findings have alsobeen reported for adults. In one study, adults were asked to give a speech and performmental arithmetic in front of a panel of judges on five separate occasions (Pruessneret al., 1997). On the first day, few associations between the individuals’ cortisolresponse to the stressor and personality measures were noted. However, associationsemerged upon repeated exposure to the stressor. As in the present study, most ofthe individuals responded to the stressor on the first trial regardless of individualdifferences in personality characteristics. However, with repeated exposure to thestressor, individual differences in responding and adapting to the stressor becameapparent. The authors concluded that novelty may “mask” the impact of personalityon cortisol response to psychological stressors.

As in the previous study, the temperament dimension of Surgency was related tothe children’s cortisol response on the fifth day of school. In the present study, onthe fifth day of school, more surgent children displayed higher cortisol levels in themorning and lower cortisol levels in the evening. While the general pattern of find-ings with the dimension of Surgency relating to HPA activity on the fifth day, butnot the first day, of school was consistent between the two studies, specific elementsof the results differed. In contrast to the findings of the present study, which includea positive correlation between Surgency and cortisol levels obtained in the morning,but not the evening, on the fifth day of school, Davis et al. (1999) found a positivecorrelation between Surgency and cortisol levels at noon and in the evening. Thus,the association between Surgency and evening cortisol levels was inconsistentbetween these studies. Similarly, the relationship between shyness, which negativelycontributes to Surgency, and evening cortisol levels was not consistent between thetwo studies. In the present study, children who were rated high in shyness displayedhigher cortisol levels on the fifth day of school as compared to weekend days.


Although the observed elevation in cortisol levels is consistent with theoreticalexpectations for the relationship between stress physiology and shyness, we believethat caution is warranted in interpreting these results as the previous study foundthat shyness was associated with lower cortisol levels on the fifth day of school(Davis et al., 1999). The reason for this inconsistency is unclear. It could be due tothe younger and narrower age range of the children studied in the present study. Thepresent study included only 6- to 7-year-olds entering first grade while the previousstudy included children between the ages of 7 and 12. There were too few firstgraders in the previous study to analyze their data separately; however, numerousfactors change in the lives of children from first grade to later grades. For example,it is likely that late afternoon and evening activities change. Older children are morelikely to receive homework and are more likely to be involved in after school activi-ties, such as social and athletic activities. Unfortunately, neither of the studiesrecorded the children’s evening activities during the first weeks of school. Recordingevening activities in future research may help clarify the associations between tem-perament and evening cortisol levels.

Interestingly, of the scales contributing to the temperament dimension of Surgency,high pleasure, not impulsivity, was the most strongly associated with cortisol levelson the fifth day of school in both studies. High pleasure is a scale that reflectsenjoyment of highly stimulating activities. Children scoring high on this scale areoften thought of as exuberant, rambunctious, and sensation-seeking. Such childrenmight find the structure of educational settings aversive and might behave in waysthat get them in trouble. Thus, the lack of fit between their temperament and thedemands of school may be one reason for their continued increased cortisol levels.Although the present study does not rule out this explanation, it provides little supportfor it. First, parent reports of behavior problems were not correlated with cortisolactivity on either the first or fifth day of school. Second, cortisol levels were elevatedcompared to weekend cortisol levels before the children left for school, but werelower than weekend cortisol levels in the evening. If the cortisol levels on the fifthday of school were the result of stressful encounters at school, we might expectelevated levels when the children returned from school, but not before they left forschool. The pattern of higher cortisol levels before school and lower levels in theevening is more consistent with a preparatory response. Although increased cortisolactivity is often associated with heightened stress, there are strains of rodents bredfor their strong novelty-seeking behavior. These rodents also exhibit marked HPAresponses after exposure to a novel environment, such as a light/dark box (e.g.,Kabbaj et al., 2000). These rodents that exhibit increased HPA responses to noveltyin conjunction with sustained exploration and novelty-seeking have a greater propen-sity to self-administer drugs and alcohol. In non-human primates, the propensity toself-administer alcohol has been found to correlate positively with the magnitude ofcortisol response to novelty and challenge (Fahlke et al., 2000). Thus, although thereis little evidence that increased behavior problems account for the prolonged alter-ation in cortisol levels for the more surgent children, the pattern of neuroendocrineactivity observed for these children may parallel associations reported in these ani-mal models.


Viewing the relationship between Surgency and cortisol in this light suggests thatsmall increases in cortisol constitute a risk factor for these children. However, itmay also be that small increases support positive adaptation. Indeed, an inverted U-shaped function has often been noted for activity of the HPA system in which toolittle and too much of a response is associated with maladaptation, but mild to moder-ate increases in cortisol support adaptive functioning (Sapolsky, 1997). As noted,although impulsivity is included in the temperament dimension of Surgency, therelationship between Surgency and elevations in cortisol at the beginning of theschool year does not appear to be mediated by behavior problems, such as violatingrules and expectations. Indeed, Surgency has been described as paralleling the per-sonality traits of extroversion and positive affectivity (Rothbart et al., 1994). Thus,the relationship between Surgency and elevations in cortisol at the beginning ofthe school year may reflect the children’s positive adaptations to the new schoolenvironment. In particular, small elevations in cortisol in the morning before school,followed by lower than typical levels in the evening, may reflect a shift in energyresources during the school day that are required to adapt to the challenges of the newschool year. In short, increases in cortisol need not signal risk. Indeed, an analysis ofthe timing of the response relative to the stressor or challenge may be important ininterpreting the biological and psychological implications of small increases in cor-tisol (Stansbury and Gunnar, 1994). For example, in a study with adolescents,researchers found that moderate elevations in cortisol in anticipation of a psychologi-cal challenge were associated with behavioral and emotional competence, whileincreases that occurred only during the challenge predicted an increase in behaviorproblems over a six-month period (Susman et al., 1997).

Overall, these results point to the importance of assessing cortisol levels acrossthe day, as variations in levels at different points in the day may bear differentrelations to temperament and individual differences in vulnerability. The results alsounderscore the importance of examining responses to repeated exposures to thestressor or challenge. Associations with temperament and personality appear tochange as individuals adapt to challenging situations. While many of the findingsrepresent an extension of earlier results, there are still some qualifications that arein order. First, although we believe the associations between cortisol levels and tem-perament reflect the children’s response to the beginning of the new school year,the results may reflect the children’s response to school in general. That is, Surgencymay continue to be related to higher morning cortisol levels throughout the schoolyear. However, when the children in the present study were in kindergarten, therewere no associations between temperament and cortisol levels on school days at themiddle to end of the school year (Davis et al., 2001). These findings suggest thatthe association between Surgency and cortisol in the present study may be specificto the first days of school. However, clearly additional research is needed. Second,the children in the present study experienced few significant life stressors in themonths prior to entering first grade and were not exhibiting clinically significantbehavior problems. In general, these children were at low risk for many stress-relatedproblems and disorders. Thus, it is unclear whether these findings would generalizeto a higher risk sample of children who encountered many major life stressors and/or


exhibited significant behavior problems. Finally, we used parent reports of the chil-dren’s temperament and behavior. Some would argue that these reports do not reflectthe children’s behavior, but rather the parents’ biases regarding the children’sbehavior (Kagan, 1998). While the associations with the children’s physiologicalresponses argue that parent reports reflect more than the parents’ subjective beliefs,it would be helpful in future studies to observe children as they adapt to new situ-ations in order to further our understanding of the relationship between individualdifferences in temperament and variations in neuroendocrine reactivity. For example,direct observation of children at the beginning of the school year may emphasizeindividual differences in children’s behavioral responses to entering a novel settingand coping strategies for managing a challenging situation that ultimately clarify therelationship between temperament and physiological responses to stress.

Acknowledgements

This research was supported by grant from the National Institute of Mental Health(MH56958) to Megan R. Gunnar. Portions of this data were presented at the 1999annual meeting of the International Society for Developmental Psychobiology. Theauthors wish to express their gratitude to the families who helped with this research.Thanks are also expressed to Mary Fowler and Linda Bailey of the Endocrine Lab-oratory at that University of Minnesota for their careful analysis of the salivarycortisol data.

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Individual differences in children's cortisol response to the beginning of a new school year