I will never forget: why emotional memories stick
Verbally abused? Attacked by a mugger? Dumped by your boyfriend unexpectedly? Chances are that you remember just about every detail of the event. What did you wear last Tuesday? What was you previous phone number? What did you talk to your mother about last time you had a long conversation? Chances are that you don't remember very many details of these latter events. But why do we remember some events in far more details than others? The short answer is that emotional events form neural networks in the brain instantly.
Different Kinds of Memories
There are many different kinds of memory. Working memory is the ability to keep information active and within reach. You use this kind of memory, for example, when you look up a phone number and remember it long enough to dial it. The frontal areas of the brain are the main neural correlates for this kind of memory.
Short-term storage memory corresponds to regions in the brain that can store information for a day or two. The main region for storing information for the short term is the hippocampus.
The hippocampus is a seahorse-shaped loop in the temporal lobe on the side of the head (strictly speaking, there are two hippocampi, one in each hemisphere). In Greek "hippo" means horse and "campos" means sea. So, "hippocampus" means seahorse. Evolutionarily speaking, the hippocampus is part of an old brain system called "the limbic system." This system is much older than (neo)cortical brain matter, the matter in the brain that generates thoughts and allows you to reason.
While the hippocampus plays a crucial function in short-term memory, it also ensure that long term memories are generated and stored in the cerebral hemispheres.
How Memories are Formed
When information you receive is stored as a memory, the brain generates a neural network by depositing proteins at the nerve endings, or axons. For these neural networks to be form, the hippocampus must normally play and re-play the information over and over again. As dream often play out recent event, these narratives may help to lay down neural networks.
The playing and replaying of information is not always necessary for a memory to be stored. When an event is emotionally intense and associated with fear, a neural network may form immediately. Emotional memories corresponding to neural networks that involve neurons in the amygdala, the brain's fear processing center. Because the neural network involve neurons in the amygdala, recalling the event will continue to activate the amydala neurons and generate fear.
Evolutionarily speaking, these fear-memory associations benefited survival. Having been attacked by a dangerous animal in a particular geographical area just once would be sufficient for a memory to be laid down. That geographical area could thus be avoided on future adventures. There can still be an advantage to having strong fear memories. Being in a verbal abuse situation, for example, may make us stay away from people who resemble our abusers. Unfortunately, our fear sometimes carries over to similar events or people that are not threatening. For example, people in an abusive marriage may avoid marriage altogether in the future because of fear. In these kinds of situations, the memory-fear associations are clearly disadvantageous.
* What are the Primary Tasks of Short Term Memory; http://www.livestrong.com/article/179067-what-are-the-primary-tasks-of-short-term-memory/
* New Mechanism of Memory Formation Discovered; http://www.sciencedaily.com/releases/2010/08/100825131556.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily+%28ScienceDaily%3A+Latest+Science+News%29
* New Understanding of How We Remember Traumatic Events; http://www.sciencedaily.com/releases/2008/10/081028103111.htm