, reverse, and retrieve memories
Two groups of mice were used in the experiment. The first were conditioned to have a fear response after receiving small shocks to their feet. Their counterparts were positively conditioned by being intermingled with female mice.
Scientists employed light to trigger the neurons responsible for the memory of the shock and subsequent fear as they placed the mice with females to test their positive reinforcement. Following this test, the mice were shown to exhibit fewer signs of fear.
Conversely, the mice with positive conditioning received shocks as scientists used light to activate neurons tied to the positive memories. As a result, these mice froze more often and sniffed less, indicating that fear had become associated with their previously positive memory. These reactions led the scientists to believe their experiment to be a success; supporting the notion that memories can be reconditioned, or conditioned to associate new emotions to a memory at the neurological level.
Additionally, two researchers at MIT used optogenetics to implant a false fear into the mind of a mouse. Scientists Steve Ramirez and Xu Liu injected a biochemical cocktail comprised of a channelrhdopsin-2 into the brains of genetically engineered mice, inserted filaments into their skulls, and used a light to locate the fear engram related to a shock to the foot. The researchers sacrificed the mouse in order to slice open its brain and see exactly how to map the engram associated with the fear of shock.
They then conditioned an experimental mouse to believe a particular box was safe, free of shocks. The next day, they put the mouse in a different box, where they were given an electric shock. The following day, the scholars put the mouse in the initial box that it believed to be safe and used light to stimulate the fear engram. Although it received no shocks and never had in that environment, the mouse immediately exhibited a fear response.
The implications for these studies are vast. Although these findings have the potential to help those with PTSD, depression, or addition, intercept bad memories and rewire them to be positive or less daunting, scientists interfering with memories introduce a host of ethical considerations.
