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UBC Theses and Dissertations

Effort-based decision making is sensitive to the effects of acute stress Shafiei, Naghmeh


Acute stress can either exert beneficial or detrimental effects on different forms of cognition, and these effects may be mediated in part by enhanced glucocorticoid and dopaminergic activity. Recent studies in humans have shown that acute stress disrupts certain aspects of cost/benefit decision making. In the following series of experiments, we assessed the effects of acute restraint stress on different forms of cost/benefit decision making, and some of the hormonal and neurochemical mechanisms that may underlie these effects. Effort-based decision making was assessed with a discounting task where rats chose between a low effort/reward lever (1 press=2 pellets), or a high effort/reward lever that delivered 4 pellets, with the effort requirement increasing over 4 blocks of discrete trials (2, 5, 10, and 20 presses). A single exposure to 1 hour stress decreased preference for the high effort/reward and increased response latencies. Control experiments revealed that these effects did not appear to be mediated by general decreases in motivation or reduced preference for larger rewards. A separate group of rats were trained on delay discounting task where they chose between a small/immediate reward (1 pellet) or a larger, 4 pellet reward delivered after a delay (0, 15, 30, 45 sec). In contrast to effort discounting, acute stress did not affect choice of larger, delayed rewards. The role of glucocorticoids in regulating effort-based decision making was assessed via the systemic administration of exogenous corticosterone (1 or 3 mg/kg). These treatments failed to mimic the effects of stress on effort discounting. In a final experiment, dopamine receptor blockade with flupenthixol (0.25 mg/kg) prior to restraint to did not attenuate the stress-induced effects on effort-related choice. However, this treatment abolished the stress-induced increase in response latencies. These data suggest that acute stress interferes somewhat selectively with cost/benefit evaluations concerning rewards of different magnitudes and the relative effort costs associated with obtaining them. These effects do not appear to be mediated by enhanced glucocorticoid activity, whereas dopaminergic activation may contribute to increased latencies induced by stress. These findings may provide insight on impairments in decision making and anergia associated with stress-related disorders such as depression.

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