Much of our knowledge about the neural circuitry of fear comes from animal studies. The amygdala mediates the ability of cues that were associated with a fearful stimulus (for example, a footshock or a predator odour) to become aversive in their own right, as established in fear conditioning and related paradigms80,81. The hippocampus mediates contextual and temporal aspects of fear conditioning82. Reactivation of memories (that is, re-exposure to the cue or context) can lead to either reconsolidation (further strengthening of the memory) or extinction, with extinction generally requiring more intensive training. Conversely, conditioned inhibition of fear, in which animals are trained to feel protected from a threat in a certain environment, induces several antidepressant-like effects in mice83. Animal studies have also made it possible to examine distinct functions of central, basolateral and medial amygdala nuclei84.
