The human amygdala and the induction and experience of fear PDF
The amygdala’s role in fear and avoidance behavior is fairly well known. Patient SM, a woman with focal bilateral amygdala lesions (the amygdala is cut off from the brain on both sides), behaviorally and subjectively reports to feel no fear in situations that would make a normal person avoid due to fear. Although SM does report to feel happiness, sadness, anger, disgust, as well as other emotions.
SM reports that fear situations are “exciting”, entertaining, amusing, and like a roller coaster ride (which SM enjoys). SM is overcome with curiosity in these situations, with approaching behavior rather than avoidance behavior. For example, although SM reports to being scared of spiders and snakes, she ambitiously picked up snakes, poked them, asked questions about the animals, and proceeded to poke larger more dangerous snakes, and tarantulas, which had the potential to bite. SM reports that these things would scare most other people, and thus seems to have an understanding of fear, as well as contextual information of fear.
My analysis is that SM is able to normally feel emotions (or so we assume since she reports having these things, and behaviorally expresses normal queues that indicate these emotions) except for fear. Fear situations seem to elicit some sort of response in SM, yet this response seems abnormal compared to the human population. SM seems to feel a “rush” coupled with curiosity, and a willingness to approach and know more about the behavior, as well as touch the “dangerous” stimuli, but no fear. In my opinion, I believe that the fear elicits the same biochemical cascade that it does in a person able to feel fear, but the modulatory behavior of the amygdala (whatever it does to make a person feel fear) is omitted due to the decoupling from the brain. Thus, the amygdala might be responsible for signals which cause the subjective experience of fear. In a normal person, the same rush occurs, but the amygdala computes the stimuli in the amygdalal center, and responds by telling the brain this is stimuli to avoid, which causes the feelings of fear (an overwhelming desire to avoid the stimuli). The amygdala responds by allowing the brain to interpret fear stimuli and cause avoidance through modulation by fear.













