Effects of stress on motivated behavior: Age differences and neural mechanics

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DESCRIPTION (provided by applicant): Stress is common in everyday life and appears to alter learning and decision making involving potential rewards and punishments. This finding that may be attributed to stress-induced enhancements of dopamine system activity. Due to age-related changes to brain structure and function, however, the impact of stress is likely to differ for younger and older adults. The long-term objective of this research is to understand how stress impacts the neural mechanisms of motivated behavior across the lifespan. This research may be used to determine older adults' ability to manage economic decisions and develop interventions targeted at addressing the needs of older adults experiencing stress. The overall aim of the proposed research is to determine the mechanisms driving effects of acute stress on learning involving rewarding and aversive feedback in normal aging. The proposed study will address these specific aims: 1) examine how acute stress affects response to positive and negative feedback, 2) examine how acute stress affects learning involving positive and negative incentives, and 3) identify the brain regions responding to acute stress via change in cerebral blood flow (CBF) from control to stress conditions. The central hypothesis of this study is that stress will exert different effects on brain regions responsible for feedback-learning in younger and older adults, but will selectively enhance the salience of rewarding outcomes in both age groups. To address these objectives, the proposed study will use functional neuroimaging to investigate acute stress effects on response to positive and negative incentives in healthy younger and older adults. The cold pressor task will be used to induce a neurophysiological stress response and repeated testing will allow for assessment of intra-individual stress responses. After the stress manipulation, participants will complete a feedback-based probabilistic learning task during functional magnetic resonance imaging. The goal of the task is to maximize gains and minimize losses by using trial and error to determine which of several novel stimuli in choice pairs are more likely to yield positive feedback (e.g., +$1) and which are more likely to result in negative feedback (e.g., -$1). Neural response to reinforcer-associated stimuli, prediction error, and feedback will be determined. Salivary cortisol levels will be used as a measure of hypothalamic-pituitary-adrenal axis reactivity to stress. In addition, cerebral blood flow will be measured at rest under stress and control conditions to examine brain regions modulated by cold pressor stress in young and old in the absence of a cognitive task. By combining neuroimaging, neuroendocrine and cognitive behavioral approaches, the proposed study will provide substantial insight into the neurophysiological mechanisms of stress effects motivated cognition in aging. PUBLIC HEALTH RELEVANCE: The findings of this study will help us to understand how the common experience of stress can alter motivation and decision making, and how these stress effects may change with age. Determining how stress affects older adults' motivation in decision making is of particular importance due to declines in cognitive function with aging and the rising number of elders faced with complex decisions about healthcare, investments, and interpersonal relationships. The results of this study will provide information about older adults' ability to manage economic decisions and may inform interventions targeted at addressing the specific needs of older adults exposed to stress.