Healthy Mind

‘I’m a Neuroscientist, and This Is How To Stop Past Thoughts From Lingering’

Photo: Getty Images / fizkes
When you're reminded of certain memories, you might feel as though you're stuck. While you might enjoy the way the smell of a certain meal evokes a sunny childhood memory, you may not feel the same way about the overwhelming cringe you feel upon recalling an awkward moment from years ago. Yes, memories can be fabulous mood boosters, but certain examples pull us out of the present moment and send us reeling down a negative thought spiral. When this happens, the rumination can make it difficult to allow for new memories—and ones that aren't clouded by past experiences—to form. But, it's possible to learn how to clear the mind of past thoughts.

Researchers have examined three modes of eliminating memories: replacing thoughts, clearing the mind, and suppressing memories. They found that suppression is the most effective effective strategy for removing the memories.

"Think of old thoughts as used, dirty dishes in our kitchen," says Jarrod Lewis-Peacock, PhD, neuroscientist and co-author of a small December 2020 study published in Nature Communications that investigated how to remove unwanted memories . "They're good—we only have limited kitchen space to prepare meals and to eat meals with. We need to use that space. But when we're done with a meal, should we just leave those dirty dishes, and silverware, and our cooking utensils just out on the counter and scattered around? Well, it's going to be harder to prepare the next meal if you don't have the dishes available. So, it's advantageous for us to reclaim those resources, so that we can use them again."

"The most effective way to stop thinking about something is to engage with it—focusing on the thing in order to change it." —Jarrod Lewis-Peacock, PhD, neuroscientist

The study enrolled 60 participants who were tasked with looking at innocuous images (think: an apple or Jennifer Aniston) and then tried to remove the images from their minds. "The study is a brain imaging study," says Dr. Lewis-Peacock. "We put people inside the MRI scanner to track what their brain is doing when they're trying to put thoughts out of the mind." The scanner allowed researchers to see how thoroughly the images were removed from the brain and how long it took to do so. The participants were prompted through three modes of memory removal: replacement (instead of thinking of the apple picture, think about what you'll eat for lunch today), clearing your mind (try to think about nothing), and suppression (actively work to stop thinking of the apple).

While replacing the thought and clearing the mind quickly removed the memory, the thought was still in the background. "It wasn't in their consciousness, but it was still there," says Dr. Lewis-Peacock. "And it lingered, and then interfered with and influenced what they were thinking about on the next trial of the experiment." But this didn't happen with suppression. "In fact, they were actually better at encoding new information," he says. "They're cleaning the dirty dishes so that they can reuse them for the next meal, if you will."

The efficacy of suppression was an interesting find, says Dr. Lewis-Peacock: "The most effective way to stop thinking about something is to engage with it—focusing on the thing in order to change it," he says. "Ignoring something doesn't make it go away."

Though the size of the experiment was small, keeping its findings in mind could prove helpful as one strategy to have in your mental-health toolkit. Given that most of us would like to forget things that are far more pressing than a picture of an apple, and thus might be tougher to suppress, Dr. Lewis-Peacock says this research isn't meant to be prescriptive.

On the flip side, Carla Manly, PhD, clinical psychologist and author, says that because the study used surface-level imagery like fruits and famous people, it's applicable to working memories, not long-term emotions. Past research on emotion suppression has shown negative impacts, like simply rebounding later.

"From a neurobiological perspective, the additional mental energy put into suppressing an unwanted thought can actually hardwire that thought into your brain," says Dr. Manly. "Whatever we think about more often—be it in a positive way or undesirable—will be encoded more deeply."

Dr. Lewis-Peacock says more research is absolutely needed. He and his team have written a grant to follow up with a series of studies looking at these three removal operations with negative and positive information. "[Further research will] answer some really important questions about whether indeed these findings translate when you have more real-world personally meaningful and emotional information," he says.

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