Amygdala microcircuits mediating fear expression and extinction

This review summarizes the latest developments in our understanding of amygdala networks that support classical fear conditioning, the experimental paradigm most commonly used to study learned fear in the laboratory. These recent advances have considerable translational significance as congruent findings from studies of fear learning in animals and humans indicate that anxiety disorders result from abnormalities in the mechanisms that normally regulate conditioned fear. Because of the introduction of new techniques and the continued use of traditional approaches, it is becoming clear that conditioned fear involves much more complex networks than initially believed, including coordinated interactions between multiple excitatory and inhibitory circuits within the amygdala.

► Transmission of information about conditioned stimuli from the lateral amygdala to fear output neurons in the central medial amygdala is indirect.
► Glutamatergic basal amygdala neurons connect the input and output stations of the amygdala for conditioned fear.
► Multiple interacting layers of inhibition control fear output neurons in the central medial nucleus of the amygdala.
► Fear extinction depends on multiple parallel mechanisms.