Researchers Reverse Emotional Associations of Memories in Mice

injection sites and the expression of the viral constructs in the Dentate Gyrus of the hippocampus (middle) and the Basolateral Amygdala (bottom corners). photo provided by MIT.

Short of time travel, there’s nothing we can do to change the past. But, with new research from MIT, there may be a way to change how we feel about it.

Neuroscientists have developed a technique to reverse the mechanism by which memories become associated with positive or negative emotions. Published in the August 27 issue of Nature, the “optogenetic” technique uses light to manipulate brain cells and control neuron activity.

Researchers tested the method using a mouse model. According to an MIT report:

Researchers set out to explore [the] malleability [of memory] with an experimental technique they recently devised that allows them to tag neurons that encode a specific memory, or engram. To achieve this, they label hippocampal cells that are turned on during memory formation with a light-sensitive protein called channelrhodopsin. From that point on, any time those cells are activated with light, the mice recall the memory encoded by that group of cells.

In the study, each mouse was exposed to either a positive or negative experience while researchers tagged associated neurons. Researchers found that they could trigger a mouse’s memory of the experience and its accompanying emotional response by applying the optogenetic technique to the part of the brain known as the dentate gyrus. A mouse’s emotional response to the memory was altered after researchers exposed it the opposite experience while simultaneously stimulating that same part of the brain.

Encouraged by the results they observed in the mice, researchers believe the technique may eventually be useful in treating human patients with disorders such as depression and PTSD.

“In the future, one may be able to develop methods that help people to remember positive memories more strongly than negative ones,” senior author Susumu Tonegawa said in the report.