Traumatic events are known to be lasting. People wake up in the middle of the night from a nightmare or everyday things may remind them of the traumatic event. But soon, people may be able to take the negative emotions associated with a memory and change it into a positive emotion.

In a study published in Nature, researchers at MIT show that they are able to change the positive or negative emotions tied to memory in mice, and are optimistic that the findings can be translated to humans.

"Recording a memory is not like playing a tape recorder, it's a creative process," said Susumu Tonegawa, senior author of the paper.

Researchers gave mice a good or bad memory of a location, and then were able to flip the memory without exposing the mice again to memory triggers.

This concept is not particularly new because psychotherapists already attempt to do this with patients suffering from depression. However, Tonegawa said it is unclear whether there is actually a neurological basis for this. These new findings shed light onto the pathways associated with memory and emotion.

In the study, scientists used genetically engineered mice with light-sensitive protein - this protein allows scientists to activate different neurons by targeting them with a laser using a technique called optogenetics.

Then, researchers exposed half of the mice to a positive stimuli and the other half to a negative stimuli. These stimuli activate the neurons that form memory in the hippocampus and neurons that form the emotions behind the memories in the amygdala.

Finally, the researchers took the mice (subjects were male) that had been exposed to the positive stimuli - interactions with female mice - and gave them a shock - the negative stimuli - while the researchers activated the neurons associated with the positive memory.

They found that they were able to make the bad memory less negative and the good memory less positive by activating certain neurons.

"Emotion is intimately associated with memories of past events and episodes, and yet the 'valence' - the emotional value of the memories - is malleable," Tonegawa said.  

Researchers found that neurons in the hippocampus could be changed to make a negative memory less negative and vice versa, however the neurons in the amygdala remained unchanged.  

Though it'll be awhile before scientists could use a technique like this on humans, researchers are optimistic that in time, it may be feasible. Until then, they are hopeful that the new information they have observed and recorded about memory associations will be applicable to developing new techniques for treating disorders such as depression or PTSD.

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