, 2007 and Rodrigues and Sapolsky, 2009).
Interestingly, blocking noradrenergic activity after cued aversive learning training does not impair the consolidation of fear learning (Bush et al., 2010, Debiec and LeDoux, 2004 and Lee et al., 2001), suggesting that noradrenergic release during training alone is sufficient to facilitate consolidation. However, noradrenergic activity appears to be necessary for the enhancing effects of stress-induced Selleck PI3K inhibitor glucocorticoids on fear learning as blocking noradrenaline during concurrent administration of glucocorticoids into the amygdala impairs cued fear memory enhancements seen with glucocorticoid adminstration alone (Roozendaal et al., 2006). This is consistent with the notion that noradrenergic signaling in the amygdala facilitates the acquisition (i.e., within-session
performance) of fear learning independently of glucocorticoids, while the consolidation of such learning relies critically on glucocorticoid activity that works synergistically with noradrenaline (Rodrigues et al., 2009). Surprisingly few studies have examined the effects of stress on cued fear learning in humans. One study showed that stress induced an hour before fear conditioning facilitated acquisition in male participants but not females (Jackson et al., 2006). Another reported that high levels of endogenous glucocorticoids (i.e., cortisol) after stress enhanced fear memory consolidation as measured by retrieval one day later (Zorawski et al., 2006). A recent study in men (Antov et al., 2013) demonstrated that stress administered prior to fear conditioning did not alter fear acquisition relative to non-stressed controls. Although group differences Imatinib did not emerge, the interval of time between the stressor and fear conditioning task did influence the effects of stress hormones on conditioned responses as measured by skin conductance. Specifically, stress administered 10 min before fear conditioning resulted in a positive association between conditioned responses and features of sympathetic nervous system arousal (i.e., blood pressure increase), consistent with the rapid noradrenergic effects typically reported
directly after stress exposure. In contrast, conditioning after a longer delay of 50 min led to a negative association between unless conditioned responses and cortisol, suggesting that HPA-axis responses at longer timescales may facilitate the recovery of a stressful experience by attenuating fear responses, as has been suggested previously (see Hermans et al., 2014 for review). Despite significant progress identifying the temporal and contextual factors that influence the learning and retention of extinction, limited studies have investigated the effects of stress on this method of fear inhibition, especially in humans. Research in non-human animals, however, has provided some insight into how these processes, along with the neural circuits that support them, may be affected by acute stress.