The titular detective of the BBC television series Sherlock possesses a “mind palace”—a highly organized mental catalog of nearly every memory he’s ever had. We mere mortals can’t match Holmes’s remarkable recollection, but when we store and recall memories, our brain activity probably looks a lot like his, according to a new study. The findings might help us find early warning signs of memory loss in diseases like Alzheimer’s.
Previous research has found that when people perceive an event for the first time and when they are asked to remember it later, the same brain regions are activated. But whether different people encode the same memory in the same way has been a topic of debate.
So scientists turned to Sherlock Holmes for answers. A group led by Janice Chen, a postdoc in the psychology department at Princeton University, and Yuan Chang Leong, a graduate student studying psychology at Stanford University in Palo Alto, California, strapped 22 study participants into a functional magnetic resonance imaging (fMRI) machine, which traces blood flow in the brain to measure brain activity. The scientists then showed them a 48-minute segment of BBC’s Sherlock. (Roughly the first half of the series’s first episode, “A Study in Pink,” for the curious superfans.) Immediately afterward, Chen asked the volunteers to tell her as much about the episode as they could.
“The first thing that struck us was just how good everyone’s memory was,” Chen says. She had initially expected most people would talk for 10 minutes or so. Instead, on average the participants spent more than 20 minutes describing the show, including the type of hat Sherlock wore, the colors in his apartment, and the relationships between the characters.
When the researchers compared the viewers’ brain activity while watching Sherlock to when they were recalling it from memory, the brain patterns were so similar that the scientists could accurately identify which scenes the participants were describing at any given time just by looking at their fMRI results. “This goes beyond just showing that some part of the brain is active during some movie scene,” Chen says. “We’re showing that there is a distinct brain pattern, like a fingerprint, for each movie scene.”
Next, the team combined all the participants’ brain activity during the perception phase into a single, average pattern. Then they compared this averaged pattern to fMRI results from individual participants’ recall phase. If everyone’s memory-related brain activity is different and individualized, then these recall patterns shouldn’t match up very well with the group’s collective brain pattern while watching the show. But the researchers found that each participant’s recall brain activity closely matched the group average during perception. That suggests that when humans experience the same events, their brains organize the memories in an extremely similar way, the researchers report today in Nature Neuroscience.
Though humans naturally share the same basic neural architecture, most scientists have thought that when it comes to memory, the big similarities are confined to “lower-order” brain regions like the hippocampus, the cerebellum, and the amygdala—things our brains have in common with most other vertebrates. The “higher-order” regions within humans’ intricate cerebral cortex are thought to contain distinctive, highly personalized brain activity for memories. Interestingly, the shared brain patterns identified in this study were found exclusively in higher-order, cortical brain regions, including the posterior medial cortex and the medial prefrontal cortex.
These findings could make cognitive scientists rethink the way they view how personalized and special our memories really are, Chen says. “We feel our memories are unique, but there is a lot in common between us in how we see and remember the world, even at the level of these brain activity patterns that we measure at the scale of millimeters,” she says.
Scientists working with memory-related neurodegenerative diseases like Alzheimer’s might be able to use this technique to identify early warning signs of memory loss or to develop more accurate, imaging-based benchmarks for memory loss, she adds.
Michael Rugg, a cognitive neuroscientist at the University of Texas in Dallas, says he’s convinced the findings reveal that our memories share some common organizational structure. Whether that’s due to memories forming in similar ways at the deep neuronal level or to people using similar strategies for recalling events will require further investigation, he says, but either way it’s “striking” how similar our brain patterns are while remembering.
“There’s a certain humbling here,” Rugg says. “We like to think of our brains and memories as being highly individualistic, idiosyncratic. … But perhaps in our brains, we aren’t the individuals we thought we were.”