Acute psychological stress can trigger normal and abnormal motivated behaviors such as reward seeking, habitual behavior, and drug craving. Animal research suggests that such effects may result from actions of catecholamines and glucocorticoids that converge in brain regions that regulate motivated behaviors and incentive processing. At present, however, little is known about the acute effects of stress on these circuits in humans. During functional magnetic resonance imaging (fMRI), twenty-seven healthy young women performed a modified version of the monetary incentive delay (MID) task, which is known to robustly engage ventral striatal and medial prefrontal regions. To induce psychological stress, strongly aversive movie clips (versus neutral movie clips) were shown with the instruction to imagine being an eyewitness. Physiological (cortisol levels, heart rate frequency, and heart rate variability) and subjective measurements confirmed successful induction of moderate levels of acute psychological stress. Brain imaging data revealed that stress induction resulted in a significant decrease in reward-related responses in the medial prefrontal cortex (PFC) without affecting ventral striatal responses. Our results thus show that acute psychological stress induces regionally specific changes in functioning of incentive processing circuits. This regional specificity is in line with animal data showing inverted U-shaped relations between levels of stress-related neuromodulators and functioning of the PFC, a structure that is believed to be critical for coordinating behavior in accordance with higher order internal goals. Our findings thus suggest that stress-related increases in habitual and reward-seeking behaviors may be triggered primarily by an impairment of such PFC-dependent cognitive control mechanisms.
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