Document Type

Dissertation

Date of Degree

Spring 2015

Degree Name

PhD (Doctor of Philosophy)

Degree In

Neuroscience

First Advisor

Natalie L. Denburg

Abstract

It is a well-known phenomenon that stress can lead to hippocampal damage and a subsequent decline in anterograde memory. We are now learning that stress may also damage the prefrontal cortex, a brain region involved in important cognitive abilities such as judgment and decision making. Notably, several of the brain regions vulnerable to increased levels of stress (i.e., hippocampus and prefrontal cortex), are also known to undergo disproportionate decline during normal aging. To date, surprisingly very little research has examined the effects of stress on the prefrontal cortex and decision-making preferences in the elderly. In order to address these gaps in the literature, the aim of the current study was to investigate how stress impacts the prefrontal cortex and decision-making preferences in a healthy older adult sample.

The first aim was to investigate the impact of acute stress on decision making in older adults. It was hypothesized that typical age-related changes in decision making would be amplified in older adults when subjected to an acute stressor, the Trier Social Stress Test (TSST). Decision-making preferences were measured by tasks that assess decision making under risk (via the Cups Task), decision making under ambiguity (via the Ellsberg Task), and temporal discounting (via the Intertemporal Choice Task). In partial support of this prediction, stress induced by the TSST affected decision making under risk and temporal discounting in older adults. After the TSST, older adults older adults displayed decreased risk-seeking when presented with a gain. Moreover, after the TSST, older adults displayed increased temporal discounting. That is, they had a decreased preference for later but larger gains (vs. smaller but sooner gains) and an increased preference for later but larger losses (vs. smaller but sooner losses). Moreover, changes in decision making varied depending on whether or not participants showed a physiological response, as measured by cortisol, to the TSST.

The second aim was to investigate the relationship between chronic stress and decision making in older adults. It was hypothesized that typical age-related changes in decision making would be amplified in older adults that evidenced higher levels of chronic stress. Chronic stress was measured by: 1) chronic stress self-report questionnaires; 2) a semi-structured chronic stress clinical interview; 3) 24-hour urinary free cortisol; and 4) diurnal salivary cortisol. Decision-making preferences were measured by tasks assessing decision making under risk (via the Cups Task), decision making under ambiguity (via the Ellsberg Task), and temporal discounting (via the Intertemporal Choice Task). Overall, I did not find strong support for the prediction that decision making and chronic stress are related.

The third aim was to investigate the relationship between chronic stress and the integrity of the prefrontal cortex in older adults. It was hypothesized that older adults who evidenced more chronic stress would have decreased volumes of the prefrontal cortex, as measured by structural magnetic resonance imaging (MRI). Chronic stress was measured by: 1) chronic stress self-report questionnaires; 2) a semi-structured chronic stress clinical interview; 3) 24-hour urinary free cortisol and 4) diurnal salivary cortisol. As predicted, perceived stress was negatively correlated with prefrontal cortex (PFC) volumes. Contrary to what was predicted, increased urinary free cortisol, diurnal salivary cortisol and positive life stressors (LES-Positive) were positively correlated with PFC volumes. Together these experiments provide some evidence to support the hypothesis that stress, both acute and chronic, impacts the prefrontal cortex and decision making among healthy older adults.

Public Abstract

Very little research to date has examined the effects of stress on decision making and the brain in the elderly. My dissertation investigated how stress impacts decision-making preferences and a specific region of the brain, the prefrontal cortex, in a sample of healthy older adults. The first aim was to investigate whether acute stress would affect decision-making preferences in healthy older adults. I predicted that typical age-related changes seen in decision making would be amplified in older adults when subjected to an acute stressor. Decision-making preferences were measured by tasks that assess decision making under risk, decision making under ambiguity, and temporal discounting. In partial support of this prediction, temporal discounting preferences in older adults subjected to an acute stressor changed. After being stressed, older adults displayed less risk-seeking. Moreover, after being stressed older adults were more impulsive when choosing between a smaller, sooner gain and a larger, later gain (e.g., preferred to gain $20 today instead of $25 in 10 days). Moreover, after being stressed, older adults discounted the future more when choosing between a smaller, sooner loss and a larger, later loss (e.g., preferred to lose $25 in 10 days rather than $20 today). Moreover, changes in decision making varied depending on whether or not participants showed a physiological response to the stressor.

The second aim was to investigate the relationship between chronic stress and decision making in older adults. It was predicted that typical age-related changes in decision making would be amplified in older adults that evidenced higher levels of chronic stress. Chronic stress was measured by: 1) chronic stress questionnaires, 2) a semi-structured interview; 3) 24-hour urinary free cortisol; and 4) diurnal salivary cortisol. Decision-making preferences were measured by tasks assessing decision making under risk, decision making under ambiguity, and temporal discounting. Overall, I found very little support for the prediction that decision making and chronic stress are related.

The third aim was to investigate the relationship between chronic stress and the integrity of a specific region of the brain—the prefrontal cortex—in healthy older adults. It was hypothesized that older adults who evidenced more chronic stress would have a smaller prefrontal cortex. Chronic stress was measured by: 1) chronic stress questionnaires; 2) a semi-structured interview; 3) 24-hour urinary free cortisol; and 4) diurnal salivary cortisol. As predicted, perceived stress was negatively correlated with prefrontal cortex (PFC) volumes, with more stress being related to smaller volumes of the PFC. Contrary to what was predicted, urinary free cortisol, diurnal salivary cortisol, and positive life stressors were positively correlated with PFC size, with more cortisol and positive life stressors being related to larger volumes of the PFC. Together, these experiments provide some evidence to support the hypothesis that stress, both acute and chronic, impacts decision making and the prefrontal cortex among healthy older adults.

Keywords

publicabstract, aging, brain, cognition, decision making, stress

Pages

xii, 172 pages

Bibliography

Includes bibliographical references (pages 139-160).

Copyright

Copyright 2015 Georgina Laurybel Moreno

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