Many people think of memory like a video, as if it were a perfect record of events to be replayed over and over again in the mind. But even as scientists have learned how very unlike a video our memories are — instead, they're subject to suggestion and change over time — they are also finding ways that we might be able to edit certain types of memory, the way we do a home movie.
Specifically, they are studying how to edit memories of fear.
In 2000, researchers at New York University discovered they could erase a fear-filled memory in rats by shocking them, and then reminding them of the fearful shock while treating them with a chemical that inhibits the creation of proteins in the brain .
The theory behind this and other experiments on animals is that a memory requires the creation of proteins when it first forms in the brain (a process called consolidation), and creates those proteins again every time it's recalled (reconsolidation).
The NYU researchers guessed that the very act of remembering destabilizes a memory, so that it can be changed or muted, according to their reports. And the results of their experiments and others support this hypothesis.
From rats to humans
Treating humans with most of these methods isn't safe, according to these studies, but researchers from NYU have recently reported being able to create a similar effect in humans by using a non-invasive technique called extinction training.
In a 2009 NYU experiment, human subjects were given an electric shock while viewing an image to give them a fear memory of the image. A day later, they were shown the image again, which should have spurred the memory to become unfixed in the brain and susceptible to erasure, according to the report.
During this "reconsolidation" window, subjects were repeatedly show the same image but without any shocks. According to the researchers, this extinction treatment was able to banish the fearful memory , even when tested a year later.
Play, pause, delete
So far, only these fear-specific memories have been shown to be affected by such editing. Fear memories and other highly emotional recollections involve a different part of the brain — the amygdala — than more run-of-the-mill memories like your grocery list or the birthdays of your family members, according to the NYU research.
In these experiments, it isn't that memories of an event are disappearing all together, but rather that the fear-aspect of the memory is being erased. In a 2008 Medical College of Georgia study, for example, researchers reported that rodent subjects remembered that a loud noise gave them a shock , but appeared to forget the specific instance and location of the shock when treated with a chemical that inhibited their brains.
In the recent NYU test on humans, the memory of seeing the image remained, but the fear associated with it was changed or deleted.