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Scientists Change Memory Emotions from Bad to Good

Scientists Change Memory Emotions from Bad to Good

We all have some things we associate with bad memories – a scent, a place, a song – but what if we could turn the negativity we feel for those things around, so that positivity is ignited instead?

Scientists from the Riken-MIT Center for Neural Circuit Genetics (CNCG) in Massachusetts in the US have managed to accomplish just that, without having to return to the place where the memory was first formed, and have published their research in Nature.

In particular, the emotions we associate with a place, be it a fondly remembered holiday or a harrowing ordeal in a particular street, can be changed by a contrasting experience. This is what therapists use when they attempt to treat people with depression or trauma victims, trying to replace the bad associations for more positive ones.

The team gave some male mice a negative experience in the form of tiny electric shocks in a particular room, and the neurons that worked to store the memory of the event were labelled using a method called “optogenetics”. This effectively installs a sort of switch inside the mice’s brains, triggered by a beam of blue light.

The following day, the mice were placed in a different room. The blue light was switched on again, “reactivating” the fearful memory from the previous day. The mice were then given the option of having the blue light on or off, obviously choosing to stay out of the part of their cage where the beam of light was.

However, the next day, the team gave the mice a positive emotional cue in the form of a female for company, to stimulate the neurons labelled with optogenetics. This was in the hope of switching the emotional reaction from negative to positive in those parts of the brain.

The mice were again given the choice of switching the light on or off, and this time opted to have it on. This was because the original memory associations has been altered for the mice and they now liked it.

And when the mice were returned to the room where their negative memories were created, they were less afraid than after the first round of testing, meaning that their memories of that room has been changed for the better.

The team was also able to establish that memory changes come when the connections between the hippocampus (for storing spatial information) and the amygdala (behind emotional responses) are adjusted. This has led to scientists now believing that a place memory can call up different groups of neurons and invoke either bad or good memories, which can be altered so that the original memory can produce a different emotional response than originally implanted.

“In our day to day lives, we encounter a variety of events and episodes that give positive or negative impact to our emotions,” said Professor Susumu Tonegawa, senior author of the paper. “So emotions are intimately associated with memory of past events, and yet the emotional value of the memory is malleable.”

The professor explained that remembering something is not simply like playing it back on a tape recorder, but instead is a creative process. And because these brain responses are alike between mice and humans, similar technology could be developed for people. “In the future,” he concluded, “one may be able to develop methods that help people to remember positive memories more strongly than negative ones.”


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