NYU neuroscientist Elizabeth A. Phelps and colleagues at Yale University find that the left amygdala responds to cognitive representations of fear
Although people learn about potentially dangerous events through hard experience (a given dog is dangerous because it once bit you), often we learn about such events through communication (a given dog is dangerous because you heard it bit somebody else.) In understanding the neural systems of fear learning, most researchers have focused on the former type of learning, which is called fear conditioning. However, little is known about the neural system underlying fear-learning through communication, in the absence of aversive experience.
Using fear conditioning, the neural systems of fear learning and expression have been eloquently mapped with both human and animal research. This research has indicated that a brain structure called the amygdala is critical to the expression of a conditioned fear response. But is the amygdala involved when you encounter a fear-invoking event that you have merely heard about?
NYU neuroscientist Elizabeth A. Phelps addressed this question by examining activity in the human amygdala with a task called "instructed fear." Using fMRI, Phelps found that the amygdala is indeed activated in response to verbally communicated "threat" stimuli. Furthermore, in this and follow-up studies, Phelps and her colleagues found that this amygdala activity is related to the physical indications of a fear response.
During "instructed fear," subjects do not actually receive an aversive stimulus, but rather they are told an aversive event might occur in conjunction with a neutral stimulus. In this case, subjects were presented a series of three images on a computer screen: a yellow square, a blue square, and the word "rest." Subjects were told they might receive a shock, delivered by an electrode on their wrist, when one color was presented (the threat condition) and that they would not receive a shock when the other color was presented (the safe condition). Although all subjects indicated that they believed they would receive a shock, none of the subjects actually received a shock during the study.
Taken as a whole, Phelps' findings extend the amygdala's involvement in the expression of fear to situations where the aversive consequences are imagined and anticipated but never experienced. In other words, fears that exist only in our minds activate some of the same neural systems as fears that are learned through experience.
This research was conducted in collaboration with Michael Davis, Christian Grillon, John C. Gore, Christopher Gatenby and Kevin J. O'Connor. These studies were conducted at the Yale School of Medicine's Department of Radiology.
Elizabeth A Phelps is an associate professor of psychology and neural science at NYU. She received her Ph.D. from Princeton University.