Here's a helpful quote from Kagan Online Magazine about how emotions "sear" info into our brains. This explains why upsetting emotions can over-ride our ability to think clearly and focus (the amygdala hijack discussed yesterday). It also explains why traumatic events can continue to haunt us long after the upset.
Why does emotion activate our attention and memory systems? Emotion is evoked when something is either good or bad, pleasant or unpleasant, painful or pleasurable. In brain lingo, emotion is a signal that something is either an opportunity or a threat. The brain is geared to pay attention to and remember opportunities and threats because that enhances our probability of survival. When there is emotion, the neurons in the brain actually fire at a higher frequency, signaling the reticular formation:"Pay Attention!" and signaling the hippocampus: "You better remember this!" Most of us remember where we were when we heard about the attack on the World Trade Center on September 11th. Why? Because the event was associated with strong emotion.
You can read the entire article here.