The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health, all the way down to our very molecules. We'll be sharing these stories over the next several weeks.

Sofie Elliott moved to Regensburg, Germany, in 2018 and rented an apartment right next to her older sister, Simone Elliott. Simone had moved to Germany as a teenager to pursue professional dance, and this was the first time in 16 years they'd lived in the same place.

The sisters had remained "best friends" in spite of the distance, and in Germany they would have long, often nostalgic talks.

"It was so interesting to go down memory lane with each other," says Simone, 36. "It was beautiful to relive some of those moments. It just sort of reminded me of where I came from."

These talks became a regular pastime — "kind of like a habit," says Sofie, 33. "We would go out and have dinner or a cocktail, and we would just get into, how did we get here?"

That curiosity would eventually lead them to confront a pivotal event from their childhood and the ways in which it shaped the women they have become. It also led to revelations about the nature of memory in general and why two people with shared experiences — even sisters who grew up together — might remember them very differently.

As they'd reminisce, the sisters began to notice that, sometimes, their memories didn't line up perfectly. Take, for example, winter ski trips with their dad.

"He would pack us into the red Astro van," Simone recalls, prompting a tart reply from her sister. "I say it's the black truck. I would swear on it," insists Sofie.

On one memorable occasion around Christmas, they were heading into the mountains when the song "Caroling Caroling" came on the radio — a favorite of the energetic sisters.

"Sofie and I loved singing this song," says Simone. "And so we were sitting in the back seat of the red Astro van" — "The black truck!" Sofie interjects — "and we were bouncing, swaying as we were singing this song. And we remember this moment that we bonked heads in the middle of that chorus. Ding, dong, ding, pow!"

The sisters still get animated as they recount the memory, as if they were watching it play out in their minds.

"But I could just swear on my life that we were in this red Astro van," says Simone, "and Sofie could swear that we were in the black pickup truck."

Remembering a dark chapter

Advisory: This part of the story refers to childhood sexual abuse.

The sisters ran into some version of the "Astro van/truck problem" over and over again: They'd both recall a memory but disagree on some details or emphasize different parts of it.

Simone says it was their first clue that memory isn't about just pulling a file from a mental archive.

"I always imagined memory like a VHS cassette that you rewind, press play and suddenly I was back in Kenmore with my sister, riding on our tricycles down the street," says Simone. "But as we started unraveling some of these stories and I would hear Sofie's perspective, there were so many pieces of it that rang true to me, even though that was not the way that I originally remembered that event happening."

As they worked through their memories, the sisters were filling in missing pieces for each other and, occasionally, as in the case of the ski trip, agreeing to disagree. It felt satisfying, they say, like they were getting a clearer picture of their own origin story.

Reconciling their memories felt especially important as they waded into one particular period of their childhood — a darker chapter that they still hadn't fully explored but that they felt ready to confront together.

"Simone and I both experienced sexual assault by the same perpetrator, who was a figure outside of our family," says Sofie. "I think I was 7 or 8. [Simone was] 10 or 11. And neither of us knew about it from each other until years and years and years later."

At first, Simone and Sofie told no one, not even each other. It was more than 10 years later, when Sofie was in college, that they discovered they had both been abused. That revelation cast a shadow over parts of their childhood and made Sofie wonder: Was their happy family really so happy?

"When I looked back on family gatherings, especially with this man being integrated into our family, I looked at them differently," says Sofie. "I started to remember the things I thought were the warm memories of my childhood, and I started to think, well, maybe they weren't so warm. Maybe they were filled with tension and fear, and I had no idea because I was a kid."

As adults in Germany, the sisters say, they discovered that they remembered the abuse in different ways.

The younger Sofie, like many who have experienced trauma, says she can visualize only bits and pieces.

"I remember so many things but not every detail," she says. "I remember the particles drifting in the air when it happened. I remember the room I was in. ... I remember really small, kind of segmented pieces about the situation."

She says the very vagueness of the memory was part of its power over her.

"Because there wasn't that clear VHS picture in my head of everything that happened. It was sort of like this dark figure that was around me, behind me, following me everywhere in my mind. I just would kind of think about the incompleteness of it all. And without being able to look it dead-on and address it, it kind of just drags around with you," Sofie says.

If Sofie was grasping for details, the elder Simone's memory was, if anything, too vivid.

"I remember the words that were said to me while being assaulted," she says. "The words that were coming out of this adult's mouth and the tone that he was taking with me and the look — I remember the way that he would look at me and would convince me that this is something very special and we have this secret and I shouldn't tell anyone."

For all those years apart, each sister was left with her own incomplete, child's-eye-view memory.

As adults, they say, they still hadn't really processed the experience or how its specter would show up in their anger, troubled relationships or struggles with alcohol. But together in Germany, they realized how important it was to fill in the missing pieces of one another's story.

"There was just so much to unpack, and it was so vital to hear each other's perspectives on this event and the way that we dealt with it or didn't deal with it," Simone says.

Sofie says they were frank with each other, in that way siblings can be. "Sometimes Simone would be like, 'Well, why do you think you're doing that?' And I would say, 'Well, you know, I don't know. Wait — no, I know.' And then we'd talk about it."

"We were putting a puzzle together," says Simone. "It wasn't heavy to talk about it. It was refreshing to talk about it."

"And each time we spoke about it, new things would pop up, and we were like, 'OK! I understand!'"

Seven Sins of Memory

Simone and Sofie became aware that memory is more complicated — more fallible and elastic — than a VHS tape pulled from an archive.

That's what was on their minds in 2022 when Simone got a call with a dream offer: the opportunity to create a full-length modern dance performance. It was a huge break for a young dancer/choreographer.

"Every day we were diving through our memories," Simone says. "That was something that was very present in our lives at the time and something that we wanted to dig a little bit deeper into."

In their digging, Simone found a book called The Seven Sins of Memory: How the Mind Forgets and Remembers, by Harvard University psychologist and neuroscientist Daniel Schacter.

What he calls "sins" are the ways that memory tends to go sideways — things like suggestibility, where a memory is skewed by later, outside influences. There's also transience (the "decreasing accessibility of memory over time"), bias (distortion of a memory through the lens of current-day beliefs) — and all the shortcuts and workarounds the human brain uses to retrieve memories.

As Simone read Schacter's book, she says it brought things into focus: Remembering is less like rewatching a recording and more like a complicated construction project.

"When we recall an event, we're taking bits and pieces of past experience and we're combining that with other information, with general knowledge of the world, our current beliefs and goals. And what we call a memory is really an emergent property, if you will, of all of those factors," says Schacter, who published an updated edition of The Seven Sins in 2021.

Each time we reconstruct a memory, the brain's whole Rube Goldberg machine gets rolling again, which effectively rewrites the memory from the point of view of our current selves.

"What initially may have been high agreement between two people in their memory for an event the day after it happened ... 10 years later, people have retrieved that event for different reasons at different times in different states, and that over time can create a divergence in how people remember that same event," Schacter says.

The "sins" offered Simone and Sofie language for what they were confronting. "It gave us clarity on our memories and helped us process the different ways that we would remember a situation, or not. It gave us something to hold on to," Simone says.

Then Simone had an idea: Perhaps the "seven sins of memory" could form the basis of the dance performance. They ran the idea by Schacter, who described his reaction as "pleased and shocked," and the sisters set to imagining what a dance performance based on the shifting puzzle of memory might look like.

Choreographing "warped memoirs"

To get from psychological concepts to modern dance, Sofie provided an intermediary. She wrote seven stories, each one based on one of Schacter's sins as well as on real memories from herself and others. She called them a series of "warped memoirs."

Simone then took each story and interpreted it as choreography, creating a seven-chapter dance piece called I Forgot to Remember.

One segment, for example, is based on Sofie's patchy recollections of the childhood abuse.

"This scene started with one woman onstage and the lights dim," says Simone, "with the dancers circling behind the audience in darkness. The audience would sort of turn their heads, noticing that something was behind them. But the figure was already gone."

The piece is meant to evoke Sofie's feelings of an elusive, haunting presence lurking behind her, and it demonstrates the "sin" of persistence — what Schacter describes as "unwanted recollections that people can't forget, such as the unrelenting, intrusive memories of post-traumatic stress disorder."

The performance, staged nine times in 2022 and 2023, was the culmination of those first long chats in Regensburg. Simone and Sofie say the whole creative process taught them to see their memories both as an artist and like a scientist.

"[You] take that memory out of your head, give it some space from you, sit in someone else's chair, look at it from all these different angles, and you're able to analyze it without so much emotional height to it," Sofie says.

"It helped us clarify, and once we saw it clearly, it was much easier to let it go," adds Simone.

More from the Science of Siblings series:

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