The Amygdala (Score 1)

This has already been brought up, but I thought I'd elucidate:

There's a part of the brain - right in the middle - called the "amygdala." The word is derived from the Latin for "almond," because surprisingly enough it looks like one.

It is believed that the Amygdala is primarily responsible for storing pain memory, and it seems to be the section of the brain least prone to forgetfulness and most easily accessed. If you fall over and scrape your knee on the playground's asphalt (or - more seriously - touch a hot stove or fall down the stairs), your brain will tuck away the memory of that pain in the amygdala. Any time a silimar situation arises (hot pot on the stove, running on asphalt, whatever) you will unconsciously recall this memory of pain.

Let me make this clear: this is a very good thing. It not only tells us what not to do, it also causes us to empathize with the pain of others. Someone already said something to the effect of: "and then we send them off to war." Exactly - how do you expect someone to make a responsible decision about killing another human being if they have very few stored memories of pain themselves?