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The amygdala is a structure in the brain usually associated with emotional states. There is, however, a strong connection between the amygdala and memory. Acting in conjunction with other parts of the limbic system, such as the hippocampus, this part of the brain helps regulate and encode emotional memories. Future behavior is often dictated by emotional memory. Associating an emotion such as fear with a particular event can help one react to dangerous stimuli, or a feeling of pleasure with a certain food can help guide future diet choices.
There are two competing theories as to how the amygdala helps emotional memory to form. The amygdala may directly encode emotional memory to some extent, working with the hippocampus. Alternately, it may provide input for memory processing performed by the hippocampus. Some researchers have even proposed a fluid integration of these theories, where the regulation of emotion and memory may actually take place using activity in both of these structures. The amygdala and memory are closely related, even if the amygdala does not form memories on its own.
Conditioning a fear response is an important link between the amygdala and memory, but this structure actually influences memory in other ways. The amygdala seems to regulate how other brain regions encode long-term memories. When larger degrees of emotional arousal during an event activate this part of the brain, the event seems to be more strongly encoded, and more easily recalled. This connection between the amygdala and memory could explain why people remember traumatic events more readily, and than those without emotional content.
The ability of the amygdala and memory to work together can be essential for survival. It is also important to note that having too strong a connection, and remembering frightening or traumatizing events too easily, can be a deficit. One theory behind post-traumatic stress disorder (PTSD) is that stressful stimuli, or stimuli similar to the initial traumatic event, overactivate the amygdala. In turn, the individual with PTSD recalls the traumatizing event, along with the negative emotions that initially accompanied it. A similar over activation could be a feature of some forms of anxiety disorders, as well.
Even positive emotions can facilitate the storage of memories. Emotional arousal of any type leads to synchronized activity in the amygdala, which could be linked to an increased ability to form neuronal connections. These strengthened connections may promote interaction that allows memories to be recalled more quickly. Larger amygdalae may have a greater ability to accomplish this feat.