Memory is a powerful thing. It can make us laugh, cry, and often cringe. Our memory is also malleable. Even though you may not realize it, when you recall memories like your high school graduation, your first kiss, or your wedding day, your brain changes that memory just slightly. Information can be updated or lost, details can be filled in or changed.
“We’re inadvertently applying filters to our past experiences,” Boston University neuroscientist Steve Ramirez told The Brink. “Memory is less of a video recording of the past, and more reconstructive.”
Our memory’s malleable nature has its share of pros and cons. Remembering false details is obviously less than ideal. But having the ability to take the sting off scary or traumatic memories is a blessing. With that in mind, scientists at Boston University want to use this memory malleability to our advantage.
In a recent study, BU researchers explored the malleable nature of memories and how activating certain “positive” memories in the brain could lessen the emotional, mental, and physical effects of “negative” ones.
If we could use our positive emotional memories to overpower negative ones, this could potentially lead to new treatment methods for individuals with mental health issues like depression and post-traumatic stress disorder (PTSD).
“Our million-dollar idea is, what if a solution for some of these mental disorders already exists in the brain? And what if memory is one way of getting there?” Ramirez posited in The Brink.
Where Do Positive And Negative Thoughts Take Place?
For years, Ramirez and his team have been studying memory in mice, and they’ve discovered where the brain stores positive and negative memories. Understanding where these memories exist—and being able to distinguish between the two—is an important step in treating memory-related disorders.
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Individual memories exist as networks of cells called engrams, and we store those memories in different areas across the brain. Ramirez’s lab focused particularly on those stored in the hippocampus, which as The Brink explains is “a cashew-shaped structure that stores sensory and emotional information important for forming and retrieving memories.”
In a new paper published in Communications Biology, Ramirez and his team of BU neuroscientists addressed the power of emotional memories. Their research found that our experiences—as well as the way we process those experiences—actually leave different physical footprints on the brain.
They mapped out all the genetic and molecular differences between positive and negative memory cells, finding that they’re mostly stored in different regions of the hippocampus. They also found that the two types of memories were quite distinct from each other and that they communicate with each other using different types of pathways.
“That’s pretty wild, because it suggests that these positive and negative memories have their own separate real estate in the brain,” Ramirez explained to The Brink. “So, there’s [potentially] a molecular basis for differentiating between positive and negative memories in the brain. We now have a bunch of markers that we know differentiate positive from negative in the hippocampus.”
How Do Scientists Activate These Memories?
The BU researchers used an advanced neuroscience tool called optogenetics, which is a method for tricking the brain cell receptors to respond to light. The first step was to make a memory by exposing the rodents to universally positive and negative experiences.
Once the mice formed new memories from those experiences, the researchers found the network of cells that held onto that experience and made that engram glow a certain color. Positive memory cell networks were green, while negatives were red or blue.
When they could see the memory, they used laser light to activate the cells. The amazing thing is that Ramirez’s team discovered they could also rewrite the negative memories by doing so.
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The researchers found that activating a positive memory, though not the only way to update a negative one, proved to be the most powerful. It also worked when they activated a neutral memory or the entire hippocampus.
“If you stimulate a lot of cells not necessarily tied to any type of memory, that can cause enough interference to disrupt the fear memory,” said the study’s lead author Stephanie Grella in The Brink.
What This Means For Mental Health Moving Forward
Artificially activating memories in humans isn’t possible, but that doesn’t mean this study isn’t beneficial. Grella said that the findings could translate to humans because you can ask people to recall something positive or negative, something you can’t do with mice.
Future research into stimulation of the human hippocampus—including experimental treatments involving psychedelic drugs like MDMA to rewrite traumatic memories—could lead to breakthroughs in the treatment of severe depression or PTSD.
“The theme here is using some aspects of reward and positivity to rewrite the negative components of our past,” Ramirez told The Brink.
The research will continue on the benefits of memory manipulation, and Ramirez and his team are working to push boundaries even further. He said they’re seeking game-changing ideas that can transform medicine, with the ultimate goal of finding solutions “way more effective” than the treatment options currently available to us.