Behavioral outputs and overlapping circuits between conditional fear and active avoidance

Abstract

Aversive learning can produce a wide variety of defensive behavioral responses depending on the circumstances, ranging from reactive responses like freezing to proactive avoidance responses. While most of this initial learning is behaviorally supported by an expectancy of an aversive outcome and neurally supported by activity within the basolateral amygdala, activity in other brain regions become necessary for the execution of defensive strategies that emerge in other aversive learning paradigms such as active avoidance. Here, we review the neural circuits that support both reactive and proactive defensive behaviors that are motivated by aversive learning, and identify commonalities between the neural substrates of these distinct (and often exclusive) behavioral strategies.

Keywords: Avoidance; Basolateral amygdala; Fear conditioning; Prefrontal cortex.

Fig. 1.

Overlapping and distinct circuits of conditioned fear and active avoidance. Conditional freezing acquired during delay and trace fear conditioning require the prelimbic cortex (PL) and medial geniculate nucleus (MgN) shown in blue, whereas trace and context fear conditioning require the retrosplenial cortex (RSC) and hippocampus (HPC) shown in red, and delay, trace, and context fear conditioning all require the basolateral amygdala (BLA) and central amygdala (CeA) shown in purple. For acquisition of learned avoidance, two-way shuttle avoidance requires the CeA, paraventricular nucleus (PVT), and infralimbic cortex (IL) shown in yellow, whereas platform-mediated avoidance requires the PL in gray, and both avoidance tasks require the BLA and Nucleus Accumbens (NAc) shown in green. We note that it is possible that more overlap exists between these circuits and may just be yet untested. It should also be noted that following long retention intervals, the RSC is needed for retrieval of delay fear (see text for details).