New Directions in the Study of Children's Memory for Stressful Events
The scientific study of children’s memory for stressful events carries numerous theoretical and practical implications. Theoretically, knowledge concerning how stress affects memory provides insight into the role that emotions and emotional regulation play in cognitive development, and into the development of narrative and autobiographical processes. Practically, how stress affects memory is relevant to evaluating child witness credibility, children’s coping with trauma, and trauma-related psychopathology (e.g., post-traumatic stress symptoms) in development. During the past two decades, numerous studies have investigated how well children remember stressful, salient personal experiences. Unfortunately, results have been mixed: Some studies suggest that stress enhances memory (Alexander, Goodman, Schaaf, Edelstein, Quas, & Shaver, 2002), whereas others suggest that stress inhibits or is unrelated to memory (Chen, Zeltzer, Craske, & Katz, 2000; Eisen, Qin, Goodman, Davis, 2002; Merritt, Ornstein, & Spicker, 1994). At least some of the inconsistencies may be due to different types of to-be-remembered events (e.g., medical procedures versus laboratory tasks) having been studied, to variations in how distress was measured (e.g., self-report, observer report), and differences in the ages of the child participants.
In a recent series of studies, we have begun controlling for these variations. We have been studying children’s memory for a laboratory procedure, the Trier Social Stress Test (TSST; Kirschbaum, Strasburger, & Langkrar, 1993), an acute stressful personal experience that involves giving a speech and completing a math task in front of two unfamiliar “scientists.” Because the TSST is standardized and takes place in a laboratory, we have considerable experimental control over what happens, and we can collect multiple measures of children’s distress before, during, and after the TSST takes place. We can also modify specific features of the TSST (i.e., at encoding) and the memory interview (i.e., at retrieval) to vary the level of stress associated with each experience. These modifications allow us to examine how stress at encoding and retrieval each affect children’s memory. Finally, our studies include children across a wide age range, enabling us to evaluate how the associations between stress and memory vary developmentally. Next we explain, in greater detail, the rational underlying our approach.
Across stress and memory studies, “stress” has been measured using a variety of approaches. In some studies, children’s self-reported distress was documented (e.g., Chen et al., 2000; Merritt et al., 1994). In others, parents or observers (e.g., nurses or researchers) rated children’s distress either during an event or retrospectively (Eisen, Goodman, Qin, Davis, Crayton, 2007; Goodman, Quas, Batterman-Faunce, Riddlesberger, & Kuhn, 1997; Peterson, 1999; Quas, Goodman, Bidrose, Pipe, Craw, & Ablin, 1999). Still in others, distress was coded according to children’s proximity to damage or threat that resulted from a negative event (e.g., Fivush, Hazzard, Sales, Sarfati, & Brown, 2003; Pynoos & Nader, 1989). Finally, in a few studies, children’s physiological responses were recorded (e.g. Chen et al., 2000; Merritt et al., 1994). The different measures of distress were often unrelated or only minimally correlated statistically (e.g., Merritt et al., 1994; Quas, Hong, Alkon, & Boyce, 2000), suggesting that they were tapping into different aspects of children’s responses to stressful events.
In our research, we have focused on children’s physiological responses as potential predictors of memory. Given that even relatively young children can mask some expression of emotion (e.g., Cole, 1986; Davis, 1995; Quas et al, 2000), we sought to examine distress via indices that were not easily amenable to volitional control. Of importance, however, we have gone beyond collecting a single, discrete measure of physiological arousal. That is, when exposed to a stressor, multiple physiological systems (the sympathetic, parasympathetic, and hypothalamic pituitary adrenal axis [HPA]) may respond. And, although the various systems’ responses may be well-coordinated at a neurological level, they are often unrelated statistically and have different implications for memory. As a result, our investigations of stress and memory have increasingly taken into account multiple types of physiological stress responses.
For example, in two initial studies, we examined the links between both sympathetic activation and parasympathetic withdrawal and children’s memory (Quas, Bauer, & Boyce, 2004; Quas, Carrick, Alkon, Goldstein, & Boyce, 2006). In one of the studies (Quas et al. 2004), we also measured salivary cortisol (a marker of HPA activation). Children completed a series of laboratory challenges that ended with a brief fire alarm sounding. Shortly afterward, children were interviewed about what happened. Sympathetic and parasympathetic responses were monitored throughout the laboratory challenges, and salivary cortisol was measured before and after the event. Sympathetic activation (i.e., sympathetically driven arousal) during the laboratory challenges was associated with enhanced memory in one study. In contrast, parasympathetic withdrawal (i.e., parasympathetically driven arousal) was associated with poorer memory in both studies, with these associations being stronger in older than younger children. Finally, larger cortisol responses to the laboratory challenges were associated with enhanced memory for the alarm.
Our initial findings are consistent with theoretical interpretations concerning the physiological systems’ functioning. Activation of the sympathetic system, commonly known as the “fight or flight” response, leads to increased blood flow to the cardiac and muscular systems and release of epinephrine, which together mobilize resources that enable an individual to respond to the threat. Theoretically, in order to determine how best to respond (i.e., whether to fight or take flight), attention should be directed towards the threat, and enhanced attention should improve memory. Parasympathetically driven arousal results from the parasympathetic system withdrawing its regulatory influences on target organs to divert resources required to respond to the threat, recover, and return to baseline (homeostatic functioning) afterward. Because resources must focus on internal self regulation, fewer are available to attend to and process external event information, which may reduce memory. Finally, activation of the HPA axis results in the release of glucocorticoids, the most important of which in humans is cortisol. High concentrations of glucorticoid receptors are located in brain regions involved in all aspects of memory. Insofar as HPA activation via glucocorticoid release increases activation in these brain regions, improved recall may result.
Despite our studies’ results fitting with these theoretical perspectives, findings remain tentative for several important reasons. For one, our findings emerged in at most two studies. One sample was small and included a restricted age range (4- to 6-year-olds; Quas et al., 2004). At the same time, the other study suggested that age may be an important moderator of the effects of parasympathetic withdrawal on children’s memory. Accordingly, research with larger samples of children across a wider age range is clearly needed. Also, in our studies, only some children exhibited increased physiological arousal to the laboratory challenges, and the magnitude of their responses was often quite small. A to-be-remembered event that reliably elicits stress responses, but is also controllable and ethical to study, is necessary to better understand how physiological stress responses relate to memory. Finally, in our initial studies, children’s memory was tested shortly after the alarm took place. It is possible that children were still aroused from the laboratory challenges and alarm while being interviewed. Children’s arousal during the memory interview, even if only moderate, may have affected their performance, independent of how distressing the actual to-be-remembered event was (Nathanson & Saywitz, 2003). To test such a possibility, it is necessary to take into account both arousal at encoding and retrieval when studying children’s memory and determine how each, directly and in conjunction with the other, relates to memory.
Arousal at Encoding Versus Retrieval
Findings from two separate studies indeed suggest that arousal at encoding (i.e., during a to-be-remembered event) and retrieval (i.e., during an interview) are differentially related to children’s memory. In Quas et al. (2004), in addition to interviewing children about the alarm shortly after it took place, as just described, we also interviewed children two weeks later. In the latter interview, we asked children about their entire initial visit (not just the alarm). We also experimentally manipulated the interviewer’s demeanor to create a more and less stressful interview context. In the high stress context, the interviewer behaved in a cold, emotionally unavailable manner. She did not maintain eye contact or smile. Nor did she provide verbal or non-verbal encouragement. In the low stress condition, the interviewer maintained a positive warm stance. She smiled, provided positive feedback, and maintained eye contact during the interview.
Children with larger autonomic stress responses (collapsed across the sympathetic and parasympathetic systems) during the laboratory challenges displayed poorer memory in the high stress interview condition, but better memory in the low stress interview condition (Figure 1). Memory performance among children with smaller autonomic stress responses, however, was unaffected by the interview condition manipulation. We speculated that children who were particularly aroused during the laboratory challenges (i.e., at encoding) were also more aroused during the high stress interview, and that the high arousal experienced during the interview then inhibited children’s memory. In other words, when under stress during an interview, it may have been difficult for children to conduct a memory search regarding what happened during their previous visit. Of interest, in the low stress interview condition, children who had been highly aroused during the laboratory challenges performed as well as children who had been less aroused during the tasks. Accordingly, it was not that the highly aroused children had failed to adequately encode the original event (because they performed quite well in the low stress interview condition). Instead, in the high stress memory interview, the formerly aroused children were unable (or unwilling) to conduct a memory search and answer questions.
Unfortunately, we did not actually measure children’s arousal during the memory interview in the study, making our interpretation regarding retrieval distress effects only tentative. However, in another study, we collected measures of arousal at both encoding and retrieval (Quas & Lench, 2007). Five- and six-year-olds came to our laboratory twice. In the first visit, they watched a fear-eliciting video. In the second visit, which took place a week later, their memory for the video was examined. During both the video and memory interview, children’s heart rates were monitored (heart rate is considered a peripheral measure of autonomic arousal; increases may be caused by sympathetic activation, parasympathetic withdrawal, or both). Again, the memory interview was conducted in either a low or high stress manner. Greater arousal while watching the video (i.e., at encoding) was associated with enhanced memory, whereas greater arousal during the interview (i.e., at retrieval) was associated with poorer memory, as reflected in increased errors when the interview was conducted in the high stress manner (Figure 2). In the low stress interview condition, retrieval arousal was unrelated to children’s memory.
Together, although our studies’ approach and samples varied, initial findings are suggestive of several intriguing and theoretically important associations between physiological arousal and memory. Arousal at encoding, especially as driven by the sympathetic system and HPA axis, may enhance memory. In contrast, arousal at retrieval, particularly that associated with parasympathetic withdrawal and perhaps caused by a stressful interview context, may inhibit memory (or at least memory performance).
Despite a relatively small number of studies examining physiological responses as predictors of children’s memory for stressful personal experiences, initial findings support the importance of continued research in this domain. We have launched a series of studies with such a focus in mind. In our studies, we have selected a to-be-remembered event that reliably elicits physiological stress responses (e.g., Dickerson & Kemeny, 2004; Federenko, Nagamine, Hellhammer, Wadhwa, & Wüst, 2004), specifically the Trier Social Stress Test (TSST; Kirschbaum et al., 1993). We modified the TSST to create both low and high stress conditions. During the TSST, we are collecting multiple measures of distress (e.g., physiological, behavioral, self report). We are also including children across a wide age range, given preliminary evidence from our and others’ studies suggesting that the associations between stress and memory may vary developmentally (Bugental, Blue, Cortez, Fleck, & Rodriguez, 1992; Quas, Carrick, Alkon, Goldstein, Boyce, 2006; Vaandermaas, Hess, & Baker-Ward, 1993). Finally, as in our previous work, we are manipulating stress not only at encoding (during the TSST), but also during the memory interview, thus enabling us to continue to disentangle the effects of stress at encoding and retrieval on children’s memory performance.
In closing, scientific research concerning children’s memory for stressful events has expanded considerably in the past two decades, and numerous exciting, innovative studies have been conducted. However, the variable results remain difficult to reconcile, in part because of methodological differences across studies. Recently, research has revealed several promising new directions for continued investigations of this important topic, one of which is reflected in our program of research. The results of our ongoing studies will contribute valuable, much-needed knowledge concerning precisely how stress likely affects children’s memory. Once these mechanisms are better elucidated, they can then be tested in relation to children’s memory for stressful personal experiences beyond those that occur within the confines of laboratory settings. Overall, our new research, along with that of other scientists, will enable a clearer, but likely complex, answer to the critical question, “How do children remember stressful events?”
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About the Authors
Jodi Quas is Associate Professor in the Department of Psychology and Social Behavior at the University of California, Irvine. She received her Ph.D. in 1998 from the University of California, Davis, and completed postdoctoral training at the University of California, Berkeley. Her work focuses on memory development and children’s involvement in the legal system. She has addressed important questions regarding how stress affects children’s memory, children’s suggestibility, consequences of testifying in court on children, and children’s emerging testimonial competence. She has received numerous awards for her research, including the 2008 APA Award for Scientific Early Career Contributions in Developmental Psychology and the 2008 APF’s Robert L. Fantz Memorial Award.
Cathy Hayakawa received dual B.A. degrees in Psychology and Criminology and an M.A. in Social Sciences from the University of California, Irvine. Her research interests concern the influence of family dynamics on young children’s social relationships and academic achievement. She has also been collaborating on a series of studies investigating social contextual influences on children’s memory development. In the fall, she will begin pursuing her Ph.D. in Child Psychology at the Institute of Child Development, University of Minnesota Twin Cities, on a Graduate School Fellowship.