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Three years ago almost to the day, my 7-year-old hugged his teacher goodbye, we walked home together, and then we pretty much remained there for the next 13 months. COVID-19 irrevocably changed all of our lives, and now that I have a little cognitive distance, I find myself wondering what we’ll remember about this time, and why.
As a science writer obsessed with the persistence of memory, it strikes me that, when I think about these years, the memories that rise above the chaff are not ones of heartache. When I look back carefully at that time of darkness, I find moments of joy, pinpricks of light.
Smell and sound are recorded more faithfully when we are in danger.
At the most basic level, episodic memory—the retention of events rooted in a certain place, time, and situational context—evolved to help us learn from experience, to problem solve, and to plan for the future.1 We have long known that strong emotion enhances the processing and encoding of a memory, yet positive and negative memories seem to serve different evolutionary functions.2
Positive ones can act as rewards in and of themselves—they help lift our mood and self-image and encourage social interactions. Negative ones tend to help us navigate dangerous situations and stay safe. That’s why some sensory details may come to mind more clearly when we recall threatening experiences.3 Studies suggest that smell and sound are recorded more faithfully when we are in danger, for example.4 We may also recall location more powerfully for negative than for positive events.5 Such sensory and place details could, theoretically, help us know what to do if we encounter a similar threat in the future.6
But in sheer numbers and longevity, positive memories seem to dominate.7 This is especially true as we age: The older we get, the more we preferentially8 hang onto our better moments.9 It turns out, this bias toward positive recollection may relate to the mutability of memory. The emotional tenor of a memory can change over the years, according to research by Richard Walker, a memory researcher at Colorado State University Pueblo. Walker has found that negative memories become less negative as time goes on.10
“Most people recover from negativity,” Walker says. “You lose a tennis match, you recover, you learn, you get better. You put the loss into perspective. You have a romantic breakup or a setback at work but you learn and move on. Yes, the event is important. But hanging onto the emotion is not as adaptive as being able to recover from it.”
The rules change, of course, when depression and anxiety are part of the equation. “Everything in the world gets filtered through what my motivational state is in a given moment,” says Vishnu Murthy, a cognitive neuroscientist at Temple University in Philadelphia. When someone views the world through a dark lens, they’ll be more likely to recall negative memories than positive ones.11 “Somebody who has a tendency for depression, or somebody with a tendency for anxiety, ends up pulling more of the negative memories into their life narrative,” Murthy says.
The older we get, the more we preferentially hang onto our better moments.
We can also leverage this phenomenon to achieve the opposite effect. Research by Mauricio Delgado, a cognitive and social neuroscientist at Rutgers University in Newark, NJ, and Megan Speer, then a graduate student in his lab, have shown that recalling happy moments triggers reward circuitry in the brain, the same circuitry that might be activated when we win a little bit of money.12 Pulling up those positive memories was enough to cause improvements in their subjects’ moods.
Researchers monitored participants’ brains in fMRI scanners as they recalled the details of specific positive and neutral events, rating each memory in terms of its emotional quality and intensity. Before and after the fMRI, the researchers gave subjects a mood assessment. “MRIs are usually boring and claustrophobic,” Delgado says, “but we had people coming out of an MRI machine saying, ‘That was fun! I enjoyed that.’”
Advancing that work, Delgado and Speer also found that happy memories can inoculate someone against stress.13 Researchers asked student volunteers to think back on either neutral or positive autobiographical events while their hands were submerged in a bucket of ice water. Those students who pulled up neutral memories experienced a surge of cortisol levels. But those who were directed to recall happy memories showed almost no change in the stress hormone.
In another experiment from Delgado’s lab, the researchers found that when they asked university students to think of a bad memory and then find a silver lining, they were able to shift the focus of their negative memories to make them more positive.14 “There is some persistence in memories, but they are labile,” Delgado says. “We can change them and update them in a way that might be helpful for emotional regulation purposes.”
Perhaps seeking out those silver linings, replaying the moments of peace and connection we find in dark times, can give us the emotional fortitude to navigate future calamities as they come. 
Lead image: Dubova / Shutterstock
References
1. Allen, T.A. & Fortin, N.J. The evolution of episodic memory. Proceedings of the National Academy of Sciences 110, 10379-10386 (2013).
2. Rasmussen, A.S. & Berntsen, D. Emotional valence and the functions of autobiographical memories: Positive and negative memories serve different functions. Memory & Cognition 37, 477-492 (2009).
3. Kensigner, E.A. & Schacter, D.L. When the Red Sox shocked the Yankees: Comparing negative and positive memories. Psychonomic Bulletin & Review 13, 757-763 (2006).
4. You , Y., Brown, J., & Li, W. Human sensory cortex contributes to the long-term storage of aversive conditioning. The Journal of Neuroscience 41, 3222-3233 (2021).
5. Mather, M. & Sutherland, M.R. Disentangling the effects of arousal and valence on memory for intrinsic details. Emotion Review 1, 118-119 (2009).
6. Bowen, H.J., Kark, S.M., & Kensinger, E.A. NEVER forget: Negative emotional valence enhances recapitulation. Psychonomic Bulletin & Review 25, 870-891 (2018).
7. Ritchie, T.D., et al. A pancultural perspective on the fading affect bias in autobiographical memory. Memory 23, 278-290 (2014).
8. Reed, A.E., Chan, L., & Mikels, J.A. Meta-analysis of the age-related positivity effect: Age difference preferences for positive over negative information. Psychology and Aging 29, 1-15 (2014).
9. Rendell P.G., et al. Prospective memory, emotional valence and ageing. Cognition and Emotion 25, 916-925 (2011).
10. Walker, R.W., Skowronski, J.J., & Thompson, C.P. Life is pleasant—and memory helps to keep it that way! Review of General Psychology 7, 203-210 (2003).
11. Joormann, J., Teachman, B.A., & Gotlib, I.H. Sadder and less accurate? False memory for negative material in depression. Journal of Abnormal Psychology 118, 412-417 (2009).
12. Speer, M.E., Bhanji, J.P., & Delgado, M.R. Savoring the past: Positive memories evoke value representations in the striatum. Neuron 19, 847-856 (2014).
13. Speer, M.E. & Delgado, M.R. Reminiscing about positive memories buffers acute stress responses. Nature Human Behavior 1, 0093 (2017).
14. Speer, M.E., Ibrahaim, S., Schiller, D., & Delgado, M.R. Finding positive meaning in memories of negative events adaptively updates memory. Nature Communications 12, 6601 (2021).
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