Reminiscing might rewrite history

Reminiscing about old times with your friends is fun, but it may rewrite history according to a new study.

Research reported in last week’s edition of the journal Science suggests comparing memories with other people sometimes alters the stored memory in the brain.

The research was conducted by Micah Edelson, a PhD student, and Professor Yadin Dudai at the Weizmann Institute of Science in Israel, who collaborated with scientists from University College London in the UK.

It has been known for some time that when people reminisce in a group, an error in memory held by one group member may be transferred to others in the group.

Sometimes, people genuinely believe the new erroneous version of events, a process known as ‘rewriting’. In other circumstances, people will outwardly agree with the incorrect story, but inwardly hang on to their original true memory.

“Humans are very social animals,” Dr Edelson said.

“We are exposed to social influences constantly; whether it is talking to friends or going to the grocery shop. So, it is important that we understand how our brains are wired to deal with socially-affected memories,” he said.

About 30 volunteers were divided into small groups to watch a TV documentary. Three days later, Dr Edelson individually tested their memories about the program with a 400-item questionnaire.

After four days, the subjects were tested again, while lying in a functional magnetic resonance imager (fMRI). This time, they were shown fabricated information for some questions, suggesting all of the other members of their group had come up with an answer contradicting their own.

The subjects changed their answers to fit with the majority view on almost 70% of occasions.

Further tests suggested for most of the altered questions, people still had their original memory intact and were just pretending or ‘fitting in’. However, in about 40% of cases, the memory seemed to have been rewritten to adopt the majority view.

The two different routes, rewriting and pretending, showed up quite differently on the brain scans. When the participants ‘rewrote’ their memories to incorporate the false information, there was heightened activity in the hippocampus, an important part of the brain which carries out vital roles in the consolidation of information from short-term memory to long-term memory and spatial navigation.

When participants were pretending, greater activity was recorded in the amygdala, which are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain.