Abstract
1. Considerable progress has been made over the past 20 years in relating specific circuits of the brain to emotional functions. Much of this work has involved studies of Pavlovian or classical fear conditioning, a behavioral procedure that is used to couple meaningless environmental stimuli to emotional (defense) response networks. 2. The major conclusion from studies of fear conditioning is that the amygdala plays critical role in linking external stimuli to defense responses. 3. Before describing research on the role of the amygdala in fear conditioning, though, it will be helpful to briefly examine the historical events that preceded modern research on conditioned fear.