Your Best Friend Is Like Google for Your Memories

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Photo: Time Stops Photography/Getty Images

There was a month this summer, as I prepared to move from D.C. to New York, when I’m fairly certain that one of my best friends — who already lived in the city — hated my guts. Like a lost but eager puppy, I regularly flooded her inbox with apartment listings, copying links into emails with subject lines like, “hi what’re your thoughts on this neighborhood” and “inside is pretty but isn’t the G train really bad???”

And bless her, she answered them … most of the time. Partly, I think, because she knew we’d be in the same city soon and I’d become less annoying, but mostly because this is what best friends do: When one is clueless, the other fills in the gaps. Form enough of a bond with someone, and their knowledge indirectly becomes yours; you have a sense of what they know, you know you can call on them to share that information, and you trust what they tell you.

Together, those three conditions form what’s known as transactive memory, a sort of brain trust where knowledge is split between two or more people. It’s like a human version of the internet: You don’t need to learn something because you can always look it up — or, in this case, ask someone else. “It allows people to have more information together than they do individually,” explains psychologist Nicole Iannone, an assistant professor at Penn State Fayette. For example, she says, “My friend’s a doctor, so I know she has this knowledge about illness. So if I’m sick, I know I can send her a text and be like, ‘Do you know what’s wrong with me?’ — knowing that she’ll be able to figure it out.”

Transactive memory is a well-documented phenomenon among couples and co-workers, but oddly enough, it’s never really been studied between friends. “There’s a ton of research on romantic relationships,” Inannone says, but “there really isn’t a lot of work on non-romantic, close relationships” — despite the fact that we call on our friends for all kinds of information: What’s a good restaurant in X neighborhood? What’s that trick you use to soothe a sunburn? What’s the name of that guy I liked senior year? Our friends can be much-needed backups for our own memories, helping us to navigate the world in general, as well as recall our own specific histories.

It’s something we know intuitively, but now research has confirmed it: In a study published last month in the Journal of Social and Personal Relationships and highlighted this week by BPS Research Digest, Ianonne and her colleagues became the first to examine transactive memories in best friends. And the closer the friendship, they found, the more interconnected the memories.

In the first part of their study, the authors surveyed 216 people between the ages of 18 and 68, asking them to rate their agreement with statements like “My best friend and I can remind each other of things we know” and “I trust that my best friend has credible knowledge.” They also answered questions about how much time they spent with that same friend, how long they’d known them, how much they trusted them, and how satisfied they were with the relationship. In the second, Iannone and her colleagues recruited 340 more people to answer similar questions, then presented them with a hypothetical situation: They and their best friend are at a trivia night, with categories like sports, music, and history. Which one of them would be the team go-to for each category? (“Both of us” and “neither” were also options.)

The trivia scenario was meant to measure the nature of the memory network the two friends shared: Was it differentiated (with each person being an expert in different things) or integrated (with two people having expertise, and filling in each others’ gaps, in the same area)? Same-gender friendships were more likely to have integrated networks, while mixed-gender pairs tended to be more differentiated. But still, the type of memory-sharing didn’t have an influence on friendship quality; what mattered was the fact that it existed at all. In both experiments, the researchers discovered, interconnected memory — more than how much time people spent together, more even than how long they’d been friends — was the factor most closely linked to the strength of the friendship.

What’s still unclear, though, is which is the cause and which is the effect: whether closeness fosters transactive memory, or whether sharing a transactive-memory system brings people closer together. “Because of our methodology, we can’t know which came first,” Ianonne says, but she suspects that “[friendship] quality breeds the strength of the system — you couldn’t just develop a transactive-memory system with any person, right? So someone you have higher friendship quality with, you might be more likely to develop this system with.

“But I think it probably also feeds back into quality,” she adds. In other words, once that shared memory network is in place, it helps people who were already close to become even closer. “It’s a loop, in a way: The stronger your system is, the more satisfied you are with your friendship because you can gain more benefits from it. It also might lead to more commitment, because it makes you more interested in maintaining that friendship.”

The researchers focused their study on networks of semantic memory (general knowledge) rather than episodic (autobiographical) memory, Ianonne notes, though both types are likely present between best friends: “For example, remembering how you became friends or remembering things you’ve done together — that could be particularly important for friendship quality,” she says. Across the board, friendships are at their best when you can rely on friends to help you understand both the past and the present, to keep track of where you’ve been and make sense of what you’re doing — when a friend, in other words, is kind of like an extension of your own mind.