Sherlock Holmes' famous memory trick really works

Sherlock Holmes remembers everything by imagining that he's storing bits of information in a "memory palace," a technique that originated in ancient Greece. Now, researchers have found that this method really does work to create long-lasting memories.

Users of the mnemonic technique, called the "method of loci," mentally navigate around a familiar place, such as a path (or Holmes' palace). To remember a piece of information, you "drop" it along the path and later retrace your steps and "pick it up." For example, if you're very familiar with Central Park in New York City, you can imagine walking through it, dropping the word "book" at the Boat House, then the word "water bottle" at the next bend, then the word "space" at the fountain. When you want to remember the words, you imagine retracing your exact steps.

By training with this method, the world's best memory champions can remember inordinate amounts of information, like word lists, digit series and decks of cards, according to the study. But the World Memory Championships test only short-term memory and only a handful of studies have looked into the brain as people use this method to improve memory.

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"We became fascinated by how such extraordinary memory performance as shown in the World Memory Championships is possible," said lead author Isabella Wagner, a cognitive neuroscientist at the University of Vienna. (One of the study co-authors, Boris Konrad — a researcher at the Donders Institute for Brain, Cognition and Behaviour in Nijmegen, Netherlands — is a memory champion himself.) 

The method of the loci uses well-known places or routes as a "scaffold" or "structure" to embed novel, unrelated information, Wagner said. The combination of prior knowledge — the familiar route — and the novel information "is very powerful to boost memory," she added.

To evaluate the method of loci, Wagner and her team enrolled 17 "memory athletes," or champions who were ranked among the world's top 50 in memory competitions, and 16 others that matched the athletes in characteristics such as age and intelligence. The researchers took functional magnetic resonance imaging (fMRI) scans of the participants' brains while asking them to study random words on a list. Then, the researchers presented the participants with three words at a time from the list and asked them to recall if the words were in the same order as previously studied. 

In the second part of the study, they enrolled 50 participants who previously had no experience in mnemonics and trained 17 of them for six weeks to recall memories using the method of loci. The rest of the participants were in the control group (16 of them were "active controls" which meant they were trained using a different memory tactic called "working memory training," and 17 were "passive controls," meaning they weren't trained at all). They again scanned the participants' brains with fMRI as they performed the same tasks, both before and after training. The researchers also asked the participants to recall which words were on the list 20 minutes and 24 hours after their fMRI scans.

The team used this test to define "weak memories," or those that could be remembered after 20 minutes but not after 24 hours, and "durable memories," or those that could be remembered 24 hours later. Four months later, the researchers retested the participants' ability to memorize and recall words.

Better memory

As expected, the participants showed better, longer-lasting memory after training with the method of loci than after training with the other memory technique or with no technique at all. The participants who trained with the ancient method showed a significant increase in durable memories, but not a significant change in weak memories (or short-term memories that faded after 20 minutes), compared with the control groups.

After 20 minutes, the people who were trained with the method of loci remembered about 62 words from the list, whereas those who were trained with the other method remembered 41 and those who weren't trained at all remembered 36. After 24 hours, the people who were trained with the method of loci remembered about 56 words, versus 30 and 21 in the control groups, respectively.

Four months later, people who were trained with the method of the loci could remember about 50 words, versus 30 and 27 in the control groups, respectively. What's more, world memory champions and the participants who trained with the method of loci showed similar brain activity as they memorized word lists and ordering.

The team also came across something unexpected: While both the world champions and the  participants were partaking in these tasks, activity in their brains declined in regions typically involved in memory processing and long-term memory, Wagner told Live Science in an email. "This was somewhat surprising to us, as better performance is typically associated with increased engagement of different brain regions," she said.

In other words, they found that less brain activation led to better memory, which may be because the method of loci prompts the brain to work more efficiently, Wagner said. In addition, while the participants rested, those who had been trained with the method of loci had increases in brain connectivity between other reasons important for storing long-term memory.

Almost anyone can learn to use the method of the loci, Wagner said. "It obviously requires time and regular practice and might thus not be suited for everyone, but it is definitely possible to 'boost' memory and reach high, or even exceptional, memory performance." 

The researchers didn't test how this training might generalize to other situations, such as remembering things other than words. Nor is it clear if the technique might help to ease cognitive decline during healthy aging or if it might be helpful for preventing or slowing disease, Wagner said. "However, we are quite excited about these results, and a whole avenue of new questions opens up that should give future studies ample material to investigate," she said. 

The findings were published Wednesday (March 3) in the journal Science Advances.

Originally published on Live Science.