The amygdala, an almond-shaped group of nuclei located in the limbic system, deep within the medial temporal lobes of the brain, is the boss when it comes to processing and storing memories of various emotions. In fact, the amygdala experiences emotions even before the conscious brain does. Repetitive triggering of the stress response makes the amygdala more reactive to apparent threats, which stimulates the stress response, thereby further triggering the amygdala, on and on and on in a vicious cycle. The amygdala serves to help form “implicit memories,” traces of past experiences that lie beneath conscious recognition. As the amygdala becomes more sensitized, it increasingly tinges those implicit memoirs with heightened residues of fear, causing the brain to experience ongoing anxiety that no longer has anything to do with the circumstances at hand.

At the same time, the hippocampus, which is critical for developing “explicit memories” —clear, conscious, records of what really happened—gets worn down by the body’s stress response. Cortisol and other glucocorticoids weaken synapses in the brain and inhibit formation of new ones. When the hippocampus is weakened, it’s much harder to produce new neurons and thus make new memories. As a result, the painful, fearful experiences the sensitized amygdala records get programmed into implicit memory, while the weakened hippocampus fails to record new explicit memories.

When this happens, you wind up with no real memory of what set you off to begin with but with a very clear sense that something bad—something very bad—is happening.