Physiological Stress Responses Associated with a Cognitive Challenge: Individual Differences and Relationship to Memory

ENNIS, GILDA E. Physiological Stress Responses Associated with Cognitive Challenge: Individual Differences and Relationship to Memory. (Under the direction of Shevaun D. Neupert, Ph.D.) Previous research has suggested that middle-aged and older educated adults have increased cortisol reactivity to cognitive challenge compared to younger educated participants and less educated adults (Neupert, Miller, & Lachman, 2006). Additional research has indicated that cortisol reactivity to laboratory stressors (i.e. the Trier Social Stress Test) may be dependent upon the personality traits of extraversion, openness and neuroticism, and that such reactivity in some cases may be moderated by gender (Oswald et al., 2006). Analyzing cortisol elevations in response to a battery of cognitive tests is important, because cortisol increases may have an influence upon assessments of declarative and working memory at the end of the testing battery. Experimental studies (e.g. Kirschbaum, Wolf, May, Wippich, & Hellhammer, 1996; Lupien et al., 1997; Lupien, Gillin, & Hauger, 1999) have suggested that cortisol elevations not related to the to-be-remembered material may generally have impairing effects upon declarative and working memory, cognitive processes dependent upon the glucocorticoid receptor rich regions of the hippocampus and prefrontal cortex (Eichenbaum, 2001; Lupien, Maheu, Tu, Fiocco, & Schramek, 2007). The effects of cortisol upon memory, however, are complex and may be dependent upon whether elevations occur in the morning or afternoon. In regards to working memory, cortisol induced impairments may also be dependent upon activation of the sympathetic nervous system (Elzinga & Roelofs, 2005; Roozendaal, McReynolds, & McGaugh, 2004). Utilizing data from the Boston oversample of the second phase of the Midlife Development in the United States, a national survey of health and well-being funded by the National Institute on Aging, cortisol reactivity associated with an in-home cognitive challenge was examined to determine whether reactivity varied according to age and education, and the personality traits of extraversion, openness, and neuroticism. Whether the effects of personality were moderated by age, education or gender was also investigated. Analyses were also conducted to determine whether cortisol increases associated with completed cognitive tests hindered subsequent performance on declarative and working memory assessed at the end of the testing battery. Whether these effects were dependent upon age and time of day of testing were also explored. In the case of working memory, sympathetic arousal, as measured by increased heart rate and sweat production, was also considered as an additional moderator. Findings suggested that highly educated older and middle-aged adults did not express an increased cortisol response over time. Of the personality variables tested, extraversion was associated with an increased cortisol response. This was further qualified by an Age X Extraversion interaction indicating that younger and middle-aged extraverted adults expressed the least change in cortisol throughout the cognitive testing period compared to older adults and middle-aged and younger adults scoring low in extraversion. Contrary to expectations, cortisol elevations alone were not significantly associated with performance on declarative or working memory testing. Working memory, however, was associated with an Age X Cortisol Change X Time of Day interaction. Results suggested that older adult cortisol responders performed better on letter-number sequencing in the afternoon than 1) same-aged participants who did not experience a cortisol increase in the afternoon and 2) same aged-participants who did experience a cortisol increase in the morning. Older adults who experienced a cortisol response in the afternoon tended to be highly educated. Further analysis also suggested that working memory performance depended upon an interaction between cortisol response and sympathetic arousal, as measured by skin conductance level and standard deviation. Those participants with increased cortisol and sympathetic arousal appeared to perform as well on letter-number sequencing as those without a cortisol or sympathetic response. Physiological Stress Responses Associated with Cognitive Challenge: Individual Differences and Relationship to Memory by Gilda Edwards Ennis A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science