In the interest of space, we do not cover contextual fear learning and regulation processes, which are known to instead rely on the hippocampus. However, we do mention specific findings from other fear learning procedures when relevant. Since stress may differentially impact different phases of fear conditioning, we discuss the effects of check details stress and stress hormones on the phases (i.e., learning, consolidation, retrieval) of fear acquisition and extinction by surveying research that has induced stress or administered stress hormones before or
concurrently with these phases. We then review the mechanisms of cognitive emotion regulation and the impact of stress in humans. Finally, we briefly review other fear regulation techniques (avoidance and reconsolidation) beta-catenin signaling where the impact of stress and stress hormones have mainly been explored in animal models. Stress is induced when real or perceived threats are detected in the environment (Joels et al., 2012). Stressors can emerge from a number of sources that can be generally categorized as physical or psychological in nature. Physical stressors comprise threats to survival
such as predatory threats that signal imminent danger, or disruptions to homeostasis such as hunger, sickness or pain. Psychogenic stressors constitute emotional or social threats that may occur through negative social evaluation or severe emotional distress (Dickerson and Kemeny, 2004). Irrespective of their source, stressors are typically characterized medroxyprogesterone by the perception of being novel, unpredictable and, importantly, outside of one’s control (Lupien et al., 2007). The detection of a stressor promotes a broad range of hormonal and neurotransmitter responses that can exert a powerful influence on brain function and behavior (McEwen, 2003). Acute stress exposure rapidly activates the autonomic nervous system through
its sympathetic branch that triggers peripheral responses, such as increased respiration, heart rate and blood pressure and allocates metabolic resources to promote defensive behavior (Goldstein, 2003 and Ulrich-Lai and Herman, 2009). This response also triggers catecholamine release by way of sympathetic nerves that activate noradrenergic terminals throughout the body, as well as the adrenal medulla that releases adrenaline directly into the bloodstream. In contrast, the hypothalamic-pituitary-adrenal (HPA) axis elicits neuroendocrine effects that peak at a longer timescale after stress exposure. Activation of the HPA-axis triggers the systemic release of glucocorticoids (cortisol in humans) that can work in a synergistic manner with catecholamines to potentiate their short-lived effects (Ulrich-Lai and Herman, 2009).