During active avoidance learning, one must learn
to first associate a CS with an aversive outcome before learning how to use a specific action to either avoid or terminate the presence of a threatening CS (see Cain et al., 2010, for review). Importantly, it has been shown that active avoidance (Moscarello and LeDoux, PD173074 in vivo 2013) and similar active, stressor controllability paradigms (e.g., Cain and LeDoux, 2007 and Baratta et al., 2007) can lead to fear reduction in the presence of a CS even when the avoidance action is no longer available. In this way, these forms of avoidance do not just regulate fear in the moment, but can be viewed as more lasting fear regulation techniques that may also change the value of the CS in future encounters. Research in rodents has revealed that the amygdala is critical to active avoidance learning
(LeDoux and Gorman, 2001 and Gabriel et al., 2003), specifically to the initial Pavlovian stage of learning. As discussed earlier, the convergence of the CS-US association occurs through plasticity in the LA and this input projects to the CE, which outputs to brainstem and hypothalamic regions that mediate fear expression and defensive responses. As avoidance training commences, projections click here from the PFC are thought to inhibit conditioned fear expression, which allow the performance of instrumental avoidance responses (see Cain and LeDoux, 2010 for review). Evidence for this comes from rodent studies showing that lesions to the IL leads to excessive fear responses and
impaired avoidance learning, with opposite results emerging from lesions of the CE (Moscarello and LeDoux, 2013). The BA can also receive input from the LA and, importantly, has direct projections to the nucleus accumbens (NA), which modulates goal-directed instrumental behavior, enabling avoidance behavior (LeDoux and Gorman, 2001). Amorapanth et al. (2000) found that LA lesions disrupted both the Pavlovian and instrumental these stage of avoidance learning. Lesions of the CE preserved avoidance learning but impaired the initial expression of conditioned responses (i.e. freezing), whereas lesions to the B led to opposite results, suggesting that pathways through the B are critical to signaling striatal circuits that facilitate avoidance learning. Neuroimaging research in humans also supports a role of the striatum in learning to avoid aversive outcomes. Participants who learned to terminate the presence of a threatening CS using a button press showed reduced levels of physiological fear arousal and amygdala activation coupled with greater activation of the striatum, pointing to a role for the striatum in aversive avoidance learning (Delgado et al., 2009).