Protect and harm: Effects of stress on the amygdala

The amygdala plays a key role in a range of adaptive social and emotional behaviors. As might be expected for a region that facilitates rapid changes, the amygdala is highly sensitive to the environment, in particular, challenges and stressors that are faced by the organism. Over short time periods, the amygdala can be primed to facilitate protective behavioral responses to stressors. However, prolonged stress experiences can lead to long-lasting changes that may be adaptive in only limited environmental settings. This chapter focuses on how acute and prolonged stress recruits and modifies the amygdala. We present evidence that stressors can produce a shift in the balance of activity and excitability of amygdala nuclei, leading to a shift in the stream of information processing through the amygdala and heightened sensitivity of the amygdala to the environment. We propose a specific set of changes in the balance between amygdala nuclei after acute stress that focuses amygdala activity towards specific stimuli, but different changes after prolonged stress that make amygdala circuits more responsive to many stimuli. This, in turn, promotes some of the behavioral changes observed after prolonged stress, such as increased sensitivity to surroundings, and loss of specificity for the environmental stimuli that are judged to be relevant. These shifts evoke emotional changes, and enhanced emotional responding, that often presents as increased anxiety.