Modified Memories

Each time we retell a story, our actual memories of its events change, says a new study.

"I don't remember being an alcoholic...but I guess if you guys say so..."

When we receive hints – true or not-so-true – about a story’s details from our friends, we often revise our version if what they say makes sense to us. But what’s incredible is, it isn’t just our retelling of the story that changes – fMRI scans show that our brains actually rewrite our memories, and we end up remembering the new version as “what really happened.”

To understand how this can work at a neurological level, a team led by Micah Edelson at Israel’s Weizmann Institute of Science gathered thirty adult volunteers, split them into groups of five, and showed those groups a short film about police arresting people. Three days later, the volunteers returned to the lab and answered a questionnaire that tested their memory of the film; and four days after that, they returned and lay in an fMRI scanner while answering more questions.

For the second questionnaire, though, the volunteers got to see “lifeline” answers, which were supposedly taken from correct responses by other participants. What the subjects didn’t know, though, was that these lifeline answers were actually incorrect answers to questions they themselves had answered correctly and confidently on the first questionnaire.

How often would you guess they revised their answers? As it turned out, a full 70 percent of the time:

Our behavioral data revealed that our manipulation induced memory errors. Strikingly, participants conformed to the majority opinion in 68.3 ± 2.9% of manipulation trials, giving a false answer to questions they had previously answered correctly with relatively high confidence.

But the researchers wanted to know if these changes reflected something deeper than a willingness to buckle to peer pressure – so they performed two more tests to check.

First, the researchers brought the subjects back into the lab a fourth time, told them the incorrect lifelines were a mix of truths and falsehoods that had been generated at random by a computer, and asked if the volunteers would like to change back to their original answers. As the subjects checked their false answers against their memories, 40 percent chose to remain with the incorrect answers to questions they’d originally answered correctly – even when they’d been sure of their correct answers to begin with.

And finally, by correlating the subjects’ answers with their fMRI data, the researchers noticed an intriguing phenomenon: as the volunteers were changing their answers from correct ones to incorrect ones, their brains showed a strong co-activation between the hippocampus – a structure known to be involved in the consolidation of long-term memories from short-term ones – and the amygdala – a structure crucial for processing strong negative emotions, such as fear, embarrassment, and sadness:

Enhanced activation in the bilateral amygdala and heightened functional connectivity with the anterior hippocampus were a signature of longterm memory change induced by the social environment. This indicates that the incorporation of external social information into memory may involve the amygdala’s intercedence, in accordance with its special position at the crossroads of social cognition and memory.

In short, it seems that as the amygdala processes scary feelings of social pressure, it signals the hippocampus to wipe and rewrite our long-term memories to fit the socially agreed-upon version of events.

You don’t need me to tell you how huge the implications of this are. How many of your own long-term memories do you think coincide with what actually happened? How much do the stories you tell yourself and others about your past  shape your and their actions in the present? In a court of law, would you stake your future on the testimony of an eyewitness?

It’s hard not to be reminded of Alan Moore’s oft-repeated comments to the effect that art – in his case, writing in particular – is magic: it reshapes people’s thoughts and memories, which reshape their perceptions of the past, present, and future – and those perceptions, in turn, reshape reality itself. It’s pretty amazing to think that you have such abilities.

But what’s really going to bake your noodle later on is, Would your brain still be doing all this if I hadn’t told you this story?

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