Scary experiences cause our amygdala, the part of our brain that processes fear, to send signals to the hippocampus, a neighboring brain section involved in long-term memory formation. The hippocampus then generates new neural cells that form the emotional memory specific to said scary experiences. In other words, when Roger the Bully threatens you for your lunch money, your amygdala reacts by causing your hippocampus to create new nerve cells specific to that experience. The next time Roger rears his terrifying head on the playground, those very nerve cells are stimulated, providing you with the emotional information necessary to analyze the experience while being stuffed head-first into a garbage can.
A damaged amygdala can therefore lead to a faulty emotional memory, since new hippocampal nerve cells won't be created. From a release:
[The researchers] labeled hippocampal cells created over a three-day period in a group of rats, and then conditioned a fear response in these rats two weeks later. They then confronted the rats with the same fearful situation or a neutral yet novel context the next day. When they examined the brains, they found that the newborn neurons had been specifically activated by the fearful situation. However, when they destroyed the basolateral amygdala, new neurons were no longer activated in response to the fearful memory.
“The research suggests that newborn neurons play a role not only in the formation of memory, but also in helping to create the emotional context of memory,” Kirby says. It also suggests that the basolateral amygdala drives the ability of new neurons to be part of an emotional memory.
According to the study authors, which include Stanford professor Robert Sapolsky, MD, this study could have useful implications regarding treatment of emotional disorders like Post-Traumatic Stress Disorder (PTSD) and depression.