Why Your Brain Forces You to Relive Your Worst Memories

Here's a fun exercise to demolish any remaining will you have to live: think about the worst memory you have. What are all the small pieces of it that come to mind? What smell or sound or feeling brings you back to that moment? What seemingly unrelated thing drags you right back into hell?

Mine is a laugh. It initially came from a woman. Kate. Middle aged with long, wavy hair, and a mouth like a straight line across her head. I worked with her years ago—we no longer speak—and still run into her every so often. When I saw her at a restaurant a few years ago, I kept it together until I heard her laugh, and had to excuse myself to go cry in the bathroom.

Months ago, I made friends with a woman who looked nothing like Kate but shared her laugh, that cackle, the one that once laughed at me so ruthlessly. It was so similar, in fact, that it triggered all the same feelings that came from being around Kate, dragged them all back from my mental cloud, and I all but stopped speaking to my new friend.

You've probably noticed trigger warnings at the top of online articles, on Twitter, or accompanying the links your friends have shared on Facebook. The point of the warning is to let you know that whatever you're about to click might enflame some past anxiety or fear—something that you thought was long forgotten but never really went away, like an old friend's laugh or an ex-boyfriend's aroma.

Nearly anyone with a history of abuse or neglect or damage knows what it's like to feel triggered: your brain, seemingly set on fire, tugs at a loose thread of an old memory you rarely want to engage with. And despite your protestations, it feels like you're right back in the moment that caused you so much grief to begin with. All it takes is a familiar smell, a taste of your past, a sound that ripples through you like a gunshot.

Whether the memory the trigger surfaces is positive or negative, the emotional impact is clear. But what's actually happening in your brain when it dredges up old memories without your explicit consent is something that hasn't been easy for neuroscience to explain. There's still a wider inability to understand how our memories are stored, hidden from us, and recalled whether we ask for them or not.

Catherine Loveday, a principal lecturer in cognitive neuroscience at the University of Westminster said that building and revisiting memories is akin to walking through a thick brush. "If you imagine walking through a really high, grassy field, and the first time you walk through, you're really having to bash through the yard," she explained. "The person walking behind you can get through a little bit more easily."

"When an association has only happened once, you won't have a very strong reaction, so that trigger won't easily set up the whole memory," Loveday continued. However, "if that association continues time and time again, it [won't] take any effort at all for one thing to trigger another." And while the idea of triggering can also be applied to good memories, the bad ones always feel more ingrained. (Do you remember how nice your mom smelled when she put you to bed, or how angry she looked when you disorganized her beloved TupperWare drawer?)

"Evolution-wise, it's very important to survive. If people treat you badly, you remember it for the rest of your life. It was one of the key evolutionary functions to keep us alive," said Ming Zhou, a professor at University of Toronto's Department of Physiology and a Michael Smith Chair in Neuroscience and Mental Health. "We remember who is not good to [us]. That's how you survive. Those people who are good to you, who don't bother your survival, you tend to not remember them," Zhou explained. So yes, it might be irrational to feel suspicious around tall, bearded men who smell like cigarette smoke, but it might be a part of your brain trying to protect yourself from having your heart broken like the first time (you go to HELL, DAVID).

According to Zhou, the best information we have about how the brain stores and recalls memory is from studying LTP, or long-term potentiation. It's the mechanism largely used for learning memory. "You read a book, you go to university—all that knowledge is part of learning memory," he said. LTP causes long-term strengthening of synapses between neurons—and stronger pathways means stronger memories, for better or for worse.

"In the case of physical injury, emotional injury, all these could trigger our LTP," Zhou said. "That is why we see people having long-term fears, long-lasting anxiety." And memories rooted in emotions are always going to feel stronger. Remember Loveday's idea of hacking your way through a grassy knoll for the first time? "The more emotional [the memory] is, the quicker and easier those associations are made," she explained. "You don't need to make so many runs through the grass."

The dream for anyone who has ever been triggered is to find whatever it is slowly eating their brain and destroy it. Accessing a triggered memory isn't exactly recalling an old memory buried in your brain; it's an unconscious reflex, something that can happen without trying. Short of tearing out pieces of your brain or waiting for the sweet, gentle release of well-deserved death, you do not have a lot of options.

"I think the only way to really get rid of them is to make new associations," Loveday said. "If you can broaden that trigger out, it's more likely to kill the other one." Does a particular smell remind you of a certain person or moment in time? Well, maybe it's time to force some new associations for yourself: wear a perfume that you once wore on bad night enough times to rewire the association, or play a once-sad piece of music during a clearly happy occasion.

Easier said than done, sure, but also easier than a lobotomy.

It's hard to say if a trigger warning actually makes a difference; Loveday suggests that it may, in fact, just prime you to be triggered, therefore making it even easier. (That, or it might convince you to avoid engaging with an article in the first place.) The brain is too complex, too unknown to make any definitive statements about what will or won't trigger something. What hurts you might not do the same for someone else. You never know who's waging a secret war inside their head.

I wish I tried harder to be friends with the woman who shared Kate's laugh. Maybe it would have helped me get over this sound that manages to make my bones clatter just by hearing it. After all, who knows what else will come around the corner, crawl into my ear, and pull all my worst memories and greatest anxieties back to the surface once again.

Jacked In is a series about brains and technology. Follow along here.