Rewriting memory, with good intent

In his lab, a scientist manipulates neurons in mice. That could help humans one day.

- CORINNE PURTILL

THE "goal of all of this is to restore health and well-being to an organism," neuroscientist Steve Ramirez says.

We often think of memories like the contents of a museum: static exhibits that we view to understand the present and prepare for the future.

The latest research, however, suggests they are more like well-thumbed library books that wear and change a little bit every time they're pulled off the shelf.

Think of one of your happiest memories. For real. Sit with the recollection. Let your mind's eye wander around the scene. See if you can feel a spark of the joy or hope you felt at the time. Let a minute pass. Maybe two.

If you played along with this experiment, you are physically different now than you were a few minutes ago.

When you began to reminisce, brain cells dormant just seconds before began firing chemicals at one another. That action triggered regions of your brain involved in processing emotions, which is why you may have reexperienced some feelings you did at the time of the event.

Chemical and electrical signals shot out to the rest of your body. If you were stressed before you began this exercise, your heart rate probably slowed and stabilized as levels of cortisol and other stress hormones decreased in your blood. If you were already calm, your heart rate may have quickened with excitement.

In either case, regions of the brain that light up when you get a reward jittered with dopamine.

The memory changed you. But by pulling this memory to mind, neuroscientist Steve Ramirez says, you also changed the memory.

Some elements of the memory heightened in importance. Others receded.

Your brain snipped out and inserted details without your conscious knowledge.

The mood you were in at the time of reminiscence left emotional fingerprints on the memory, as neurons activated by your mental environment synced up with those activated by the recollection.