WE ALL HAVE bad memories.

And, while some are considered learning experiences, there are others that we’d sooner forget.

Thankfully, scientists from Japan and the US have discovered just how to do that. And they could use it to treat disorders such as post traumatic stress.

“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 US, used optogenetics — a new brain-control technology which utilises 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 science

In the experiment, researchers injected a light-sensitive algae protein into two groups of mice.

This allowed researchers see when a memory was being formed. While this was happening, one group was allowed play with female mice, forming a positive memory while the other was shocked.

Researchers then artificially reactivated the memory using the light pulses — effectively making the mice remember what had happened to them.

While the mice were “remembering” their event, they were given the opposite experience — the mice with the nice memory got a shock, while those with the painful memory were introduced to 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.

The researchers hope their findings might open up new possibilities for treatment of mood-affecting disorders such as depression, or PTSD, a condition found in people such as soldiers who have undergone life-threatening or particularly horrific events.

“In the future, I would like to think that with new technology we will be able to wirelessly control neurons in the brain, without intrusive tools like electrodes,” said Tonegawa, who won the Nobel Prize for Physiology and Medicine in 1987.

“We could possibly augment good memories over bad ones,” he said.

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