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Scientists 'Rewrite' Bad Memories in Mice

Manipulation of brain cells can switch negative emotions to positive ones, researchers say


Two days later, the mice were placed into a large arena. The researchers recorded which half of the arena the mice naturally preferred, and then began stimulating the dentate gyrus cells with light as the mice wandered around the arena.

Mice conditioned with fear received memory stimulation whenever they were on the side they naturally preferred, and they soon began avoiding that area. On the other hand, mice with happy memories received stimulation when they wandered into the area they preferred less, and they ended up feeling better about that location and spent more time there, the study found.

Researchers then tried to reverse the emotional responses stored in the rodents' brains. For male mice with fear conditioning, the researchers light-activated the memory cells involved in the fear memory while the mice spent pleasant time with female mice. For mice that had initially received the reward conditioning, memory cells were activated while they received mild electric shocks.

The reversal worked, and the mice ended up switching the side of the arena they preferred when their memories were stimulated by light.

Subsequent attempts to alter emotional memories through manipulation of the amygdala didn't work, suggesting that emotions are hard-wired into individual cells inside the amygdala, the study authors noted.

Dr. Scott Turner, a professor of neurology at Georgetown University, said understanding how memory and emotion intersect could be key to treating people with post-traumatic stress disorder (PTSD).

"If you could find ways to reverse the [emotion] associated with a particular memory so it isn't so negative, you could help these people suffering from stressful memories," Turner said. "Obviously, we're a long way from that, since this study was performed in mice."


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