Light Turns Bad Memories Into Happy Ones

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Memories are often associated with emotions, and these feelings can change through new experiences and over time. Now, using light, scientists have been able to manipulate mice brain cells and turn the animals' fearful memories into happy ones, according to a new study.

Memories are encoded in groups of neurons that are activated together or in specific patterns, but it is thought that neurons in different brain regions encode different aspects of a memory of an event. For example, the place where an event occurred and the emotion associated with it may be stored in different places.

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The premise of Assassin's Creed is the reliving of other people's memories stored inside DNA. Well, scientists have found that in mice this actually happens!

In the new study, researchers examined whether it is possible to selectively change one part of a memory — the emotion attached to it. They made male mice form fearful memories by giving them painful electrical shocks, or form pleasant memories by letting the animals interact with female mice. [Why You Forget: 5 Strange Facts About Memory]

Later, using light to control the activity of neurons (a method called optogenetics), the researchers evoked the fearful memories every time the mice went to a certain corner of their cage, which led the mice to avoid that corner. In mice that had formed pleasant memories, the researchers used those memories to make a certain corner look attractive to the rodents.

In the last step, to reverse the associations between a place and an emotion, the researchers evoked only the "place" part of the fearful memories, while letting the mice interact with female counterparts. As a result, the mice were no longer afraid of that specific corner of the cage.

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The researchers were also able to do the reverse, and turn positive memories to fearful ones, according to the study published today (Aug. 27) in the journal Nature.

Shaping Memory Fragments

It is well-known that memories are subject to change, and may even get slightly rewritten each time we recall them during a new experience, studies suggest.