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If you've ever fantasized about banishing certain memories from your brain forever (and really, who hasn't—I think we could all just go ahead and zap away all middle-school-borne trauma) your dream is thisclose to becoming a reality.
A new study hailing from MIT neuroscientist eggheads has revealed some fascinating insights into our brain circuitry, mapping the way memories become linked with positive or negative emotions. Published recently in Nature, the study has demonstrated that the connection between the hippocampus and the amygdala can be actively manipulated with optogenetics—a new technique that uses light to control neuron activity.
The findings could revolutionize modern psychiatry, offering newfound methods for alleviating the crippling symptoms of mental illness and revealing the exact brain circuitry to target with drugs. As more than 25 million Americans will experience PTSD at some point in their lifetimes, the capability to dispel memories that render some people utterly incapacitated and miserable would be no small feat.
How Memories Are Formed
The factual information of a memory (for example, a location, time of day or something said) is stored in the hippocampus, while the emotions associated with said memory are stored in the amygdala. The key to manipulating memories is understanding the connection between these two facets of remembering.
How do we alter the emotions associated with a negative memory?
While memories—like reality—are infinitely malleable and are actively altered by psychologists to ease patients' suffering from PTSD or depression, we've yet to understand how or why this process happens on a neurological level. Until now.
Helmed by Susumu Tonegawa, director of the RIKEN-MIT Center for Neural Circuit Genetics at MIT’s Picower Institute for Learning and Memory, researchers have made leaps in memory manipulation that can only be likened to the seeming science fiction proffered in Eternal Sunshine of the Spotless Mind; Tonegawa and his team were able to tag neurons that encode a specific memory, also known as an engram.
The researchers used the aforementioned process of optogenetics, that is, the labeling of cells in the hippocampus that are "turned on" during memory formation with a light-sensitive protein known as channelrhodopsin—then, voila! Any time those cells were activated with light, the subjects (mice) were forced to recall the memory encoded by that very same group of cells.
While Tonegawa’s lab was able to implant, or “incept,” false memories in mice (seriously) by reactivating engrams while the mice were undergoing a different experience (thus replacing their previous memory with a new one) the new study went one step further.
The team took a batch of mice and exposed some to fear conditioning (mild electrical shock) and some to reward conditioning (male mice got to hang with sexy female mice). The scientists were able to tag those neurons associated with both fearful memory and pleasure, enabling them to theoretically induce those positive or negative memories just with light.
All the mice were then placed into a large rectangular area and for three minutes, the researchers recorded which half of the arena the mice naturally preferred. For mice that had received the shock treatment, the researchers stimulated the labeled cells with light whenever the mice went into the preferred side, inducing some sad memories. The mice—poor bastards—soon began avoiding that area, illustrating that the reactivation of the fear memory had indeed been successful.
"I remember," thinks the mouse, "that when I'm in this area, I experience pain." The theory is, of course, that even when there is no pain, the mice will experience fear and anxiety surrounding that part of their cage anyway. It's basically an induced form of mild PTSD.
Happily, scientists were able to accomplish the reverse as well, transforming a negative memory into a cheerier one. Whenever the reward-conditioned mice wandered over to their inherently less-preferred side of the cage, the scientists "lit up" their memory of hanging out with the ladies; soon enough the male mice began hanging out more in that section of the cage because they were recalling fond memories of flirting.
Moreover, those mice who were initially electrically shocked were allowed to hang out with the lady mice while the scientists induced their fear memory for 12 minutes. When reintroduced to the cage however, the once fearful mice that would avoid one side of the cage at all costs no longer did; their memory of pleasant lady-mice was able to subsume their previous memory of fear—the key lies in the simultaneity of the two experiences.
The fact that a positive memory can indeed begin to weaken the negativity surrounding a particular event is exciting indeed. According to Tonegawa:
“That plasticity of the connection between the hippocampus and the amygdala plays a crucial role in the switching of the valence of the memory.”
What this implies for the conspiracists of the world who know that the government has been waiting for the dawn of this technology to systematically induce societal-wide memories of pleasure in giving them money or perhaps make us feel miserable when we protest . . . well, they've got some busy—and worrisome—days ahead.
