Scientists say it’s possible to overwrite bad memories

By Katie Forster, AFP

TOKYO–Emotions connected to memories can be rewritten, making bad events in the past seem better and good things appear worse, scientists from Japan and the United States have found. The discovery of the mechanism behind the process helps to explain the power of current psychotherapeutic treatments for mental illnesses such as depression or Post Traumatic Stress Disorder (PTSD), they said, and could offer new avenues for psychiatric help. “These findings validate the success of current psychotherapy, by revealing its underlying mechanism,” research leader Susumu Tonegawa told AFP in Tokyo.

The team, formed from a collaboration between Japan’s RIKEN institute and the Massachusetts Institute of Technology in the U.S., used optogenetics — a new brain-control technology which utilizes light — to better understand what happens when we reminisce. They found that warm feelings or intense fear triggered by the interaction between the hippocampus — the brain’s diary room — and the amygdala — the place believed to encode positivity or negativity — are more flexible than previously thought. “It depends on how strongly the (good or bad aspect) dominates … there is competition between the two circuits’ connection strengths,” Tonegawa said. The researchers injected two groups of male mice with light-sensitive algae protein. This allowed them to identify the formation of a new memory as it was happening and then use pulses of light to reactivate it when they wanted to. One group of rodents were allowed to play with female mice, creating a positive memory. The other group were given a small but unpleasant electric shock through the floor. Painful Memory