Fear Learning

This chapter focuses on the biological basis of fear learning. Fear triggers an ensemble of defensive mechanisms that are critically important for survival. One way to study fear in the lab is to use Pavlovian fear conditioning. In this paradigm, an initially neutral stimulus, such as a tone, is paired with an aversive footshock. After even one pairing, subsequent pres entation of the tone alone produces a range of conditioned fear responses (including freezing, fear-potentiated startle, changes in heart rate, etc.). Early on, it was recognized that the amygdala is critical for fear learning. Pioneering work in the 1980s and 1990s identified the pathways to the amygdala that transmit sensory information and pathways from the amygdala that mediate the expression of conditioned responses. Building on this anatomical foundation are experiments showing the links between fear conditioning and long-term potentiation (LTP) within the amygdala. These experiments showed that potentiation of conditioned thalamic inputs in the lateral amygdala may underlie conditioned fear. Finally, we review the molecular mechanisms whereby the amygdala encodes and stores the associations learned during conditioned fear. Long-term fear memory, like many other forms of long-term memory, critically relies on new protein synthesis. The transcription factor CREB has been shown to be particularly important in this process. These results provide important cellular and molecular insights into fear learning.