They’re not so different after all Hartswood Films/REX/Shutterstock

You might think your memories are unique, but a study involving a Sherlock Holmes drama suggests the opposite. When people describe the episode, their brain activity patterns are almost exactly the same as each other’s, for each scene. And there’s also evidence that, when a person tells someone else about it, they implant that same activity into their brain as well.

That’s the implication of a groundbreaking experiment which, for the first time, has revealed that when we record and recount a shared experience, we use practically the same brain activity as each other, rather than everyone remembering and recalling events in random, individual ways.

“We feel our memories are unique, but we see now that there’s a lot in common between us in how we see and remember the world, even at the level of brain activity patterns,” says Janice Chen at Princeton University.


Detective story

Aptly, the legendary detective Sherlock Holmes and his sidekick, Dr Watson, played a key part in the discovery. That’s because the phenomenon came to light when 17 volunteers had their brains scanned as they watched, then immediately recalled, a 50-minute episode of the BBC drama, Sherlock.

Chen and her colleagues broke down the episode into 50 distinct scenes, and analysed the brain activity of each individual while they viewed and recalled them.

“We were very surprised how good people’s memories were, with many people speaking for over 30 minutes, hitting most of the scenes in mostly the right order and giving lots of detail,” says Chen.

Incredibly, brain activity while watching, and later recalling, each scene was strikingly similar across all 17 volunteers. Chris Bird at the University of Sussex, UK, says this discovery is “extremely surprising”. The patterns of brain activity for particular sections of the drama appear to create a “signature” that is common across individuals.

During their verbal accounts of the episode, the volunteers even appeared to edit their memories in an identical way, in terms of which parts of the original brain patterns were cut and which retained. This editing meant that even though the volunteers used diverse words, sentences and recollections to articulate their accounts of what happened in the episode, the brain activity patterns during recall across the 17 viewers closely matched each other.

“It’s a kind of whittling down to the gist of what happened,” says Bird. “Once you’ve edited it, there’s a clearer thing to pass on.”

Implanting memories

Chen says the experiment was far more ambitious and sophisticated than many previous attempts to interrogate memory circuitry, as these often rely on recall of simple objects. “We’re showing here that there’s a distinct brain pattern for each movie scene,” she says. “Usually, memory experiments use single words or static pictures, so we’re excited to show it’s possible to do all this during a much more realistic experience, watching an hour-long movie and talking freely about it for many minutes.”

But Chen dismisses the idea that the discovery could be exploited to artificially implant memories into people’s brains, as has been done in mice.

However, in ongoing research in which people who haven’t seen a movie listen to someone else’s description of it, Chen and her colleagues have found that the listener’s brain activity looks much like that of the person who has seen it.

“I would say that you implant your thoughts into another person’s brain quite easily, simply by telling them what you are thinking or remembering,” says Chen. “You remember it and, at the same time, they imagine it.”

A key implication of the discovery, says Chen, is that this “universal recording network” evolved to enable us and our evolutionary ancestors to instantly understand and empathise with one another, essentially implanting memories in each other’s brains by recounting stories and information crucial to survival.

“I think this is no accident, because having a common framework for remembering makes it easier to communicate our memories to others, and that’s a powerful thing human beings can do,” says Chen. “If I direct a stranger to a train station, for example, that stranger would be using my brain to process information from the world, taking a shortcut to acquiring knowledge.”

Journal reference: Nature Neuroscience, DOI: 10.1038/nn.4450