Emotions connected to memories can be rewritten, study finds
Emotions connected to memories can be rewritten, making bad events in the past seem better and good things appear worse, scientists have found.
The discovery of the mechanism behind the process helps to explain the power of psychotherapeutic treatments for mental illnesses such as depression or post traumatic stress disorder (PTSD), they said, and could offer new avenues for psychiatric help.
The team, a collaboration between Japan's Riken institute and the Massachusetts Institute of Technology in the US, used optogenetics - a new brain-control technology which employs light - to better understand what happens when we reminisce.
They found that warm feelings or fear triggered by the interaction between the hippocampus - the brain's diary room - and the amygdala, 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," research leader Susumu Tonegawa said.
The researchers injected two groups of male mice with light-sensitive algal 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.
Researchers then reactivated the memory using the light pulses - effectively making the mice remember what had happened. While the mice were "remembering", they were given the opposite experience - the mice with the nice memory got a shock, while those with the painful memory played with females.
Tonegawa said his team had discovered that the emotion of the new experience overpowered the original emotion, rewriting how the mice felt about it.