According to research people are more likely to remember tragic and sad events than happy events like anniversaries and birthdays. Functional magnetic resonance imaging has shown that negative events stimulate activity in the emotion-processing regions of the brain like the orbitofrontal cortex and amygdala. This is the reason that people witnessing an assassination are more likely to remember the gun, but may not remember their surroundings. This tendency to remember bad memories is considered to be an evolutionary tactic which protects humans against future life-threatening or negative events.
