"The cells in your body are turning over quite often, so your red blood cells only last 120 days. Your hair gets turned over every few years, your skin cells only last 2 or 3 weeks, the colon and the stomach, it's only 4 or 5 days before all of those cells get replaced. Now, neurons, the cells in your brain, those don't die and get replaced, but the atoms that make them up are constantly turning over. So when you look at your friends and loved ones, atomically, they've completely turned over from when you last saw them, let's say 5 years ago. Memories can drift around a little bit . . . When you have a very salient emotional event, those memories are unerasable. But, these flash bulb memories are no more reliable than other types of daily memories (because each time we think about them we corrupt them). Even trauma memories eventually fade . . . the rate of your heartbeat, the architecture of your brain, even your DNA changes over the course of a lifetime. We have all these things that make us feel as though we have a consistent identity through our life and, in fact, you are not staying the same. You are changing all the time. We have this illusion of continuity."
- David Eagleman, Baylor College of Medicine neuroscientist