"We are what we remember," says Michael Anderson, a professor of cognitive neuroscience at Cambridge University who studies memory. How you remember your life as an 80-year-old depends on how you hold onto or let go of memories. Your brain is always about to forget, but Anderson believes that you can forget with more intent – what he calls motivated forgetting – and that with practice, you can do better. "You shape your memories," he says.
Memory is based on what cognitive scientists call recall cues. Say you're trying not to think about a painful breakup, but then the same kind of blue Prius your ex drove stops at a red light next to you. Memories pour in. If you are trying to forget something, prepare yourself for the recall cues from that memory so that you can reshape the way your brain reacts to them. You can try to avoid such triggers, but this strategy rarely works. A Vietnam War veteran might take care to avoid anything reminiscent of warfare and still be put back in combat images while trying to order dinner in a restaurant. "How can you imagine a bamboo placemat would remind you of a war?" Says Anderson.
Try a technique called thought substitution instead of avoiding getting clues entirely. If you've had a bitter argument with your sister and think about it every time you see her, work on focusing on other, more positive associations. Practice until your brain sees their face and those better memories pop up first and not the fight. You can also work on what cognitive scientists call direct suppression. "You just raise your mental hand and say," No, I don't want to think about that, "says Anderson. While these two forgetting mechanisms often work together, they are neurologically different. Thought substitution relies on the left prefrontal cortex – direct suppression right.
Your ability to forget is determined in part by your specific neural architecture. Studies also show that extreme stress and lack of sleep make motivated forgetting worse. People who have experienced more adversity in their life are better at it than people who have not known such difficulties. If you have experienced something traumatic, it is unlikely that you can completely erase the experience from your brain. What you can do is limit the extent to which these memories invade unwantedly.