Learning to remember


Filed under Neuroscience

Pollux statue, via Flickr/Yellow.Cat. Although Castor and Pollux were both sons of Leda, they had different fathers. Castor was the son of the mortal Tyndareus while Pollux was the son of Zeus, who seduced Leda disguised as a swan. When Castor died, Pollux asked Zeus to let him share his immortality with his brother, and so they became the constellation of Gemini.

Legend goes that the Greek poet Simonides of Ceos was having dinner at the house of a wealthy man in Thessaly when he received a message to go outside to meet two men who had requested to see him. When he left the room, the roof collapsed, killing the host and all the other guests. Although the corpses had been crushed beyond recognition, Simonides realized he could identify all the dead by simply remembering the place where they were seated at the table. This tragic event, as recalled by Cicero, became the origin of what is now known as the method of loci, a system which allows to remember things – numbers, words, items – by mentally associating them with a physical location. More than 2,000 years later, the system still proves effective and it’s widely used by champions of memory contests, among others.

The method works by linking the items to be remembered with a well known physical place, such as our own home. Then, as we picture ourselves moving around this familiar scenario, our brain can easily retrieve each of the items.

Memory can be trained through exercises like the method of loci. But how does this training shapes our brains? What are the changes that allow us to retrieve information more easily? Functional magnetic resonance imaging (fMRI) experiments had already shown that when individuals use the method of loci they activate the same regions of the brain that are used to process visual information about where objects are in space. Now, a recent paper published in Neuron sheds more light on the issue. Researcher Martin Dresler and his team analysed 1 the brains of memory champions, as well as those of regular people before and after memory training using the method of loci. Their results indicate that memory training alters the brain’s pattern of connections and that these changes are long-lasting.

Practice makes perfect

One of the authors of the study, Boris Konrad, was one of the top-ten memory athletes in the world only a few years ago. Konrad is today a postdoc a Dresler’s lab, but he is also one of the 23 memory athletes who had their brains scanned both at rest and while engaging in a memory task. For each of these athletes there was another individual matched for age, sex, intelligence and handedness, but without any prior memory training experience, that acted as a control.

One of the researchers’ first observations was that, anatomically, the athletes’ brains were similar to those of regular individuals. So unlike what happens with muscles, neither the whole brain nor specific brain regions seem to grow in size in response to training.

As expected, when these memory athletes were subjected to a 72-word learning task they outperformed control individuals by large – most of the athletes could correctly recall all 72 words, while the average individual could only remember about 40.

In the second part of the study, 51 male participants, aged between 21 and 27, and without any prior experience in mnemonic strategies, were divided into three groups. The first group received a six-week memory training using the method of loci. A second group consisted of what the authors called an “active control”, where they were subjected, also for six weeks, to a memory task called dual n-back, which trains short-term memory but does not provide a systematic method for remembering things. A third group, termed “passive control”, did not train at all.

The participants performed the 72-word learning task and had their brains scanned both before and after the 6-week period. The results showed that those who trained using the method of loci improved greatly their memory abilities, being able to remember, on average, 35 words more than without training. Not only that, but when these participants were asked to take the test again 4 months later, they were still able to remember about 20 words more than the first time, even without having trained throughout that period.

Reshaping the brain

In addition to the memory tests, all participants were subjected to fMRI scans, a technique that detects blood flow changes in the brain. By monitoring these changes, researchers can infer which areas become activated in response to specific tasks.

The volunteers’ brains were compared to those of the memory athletes at three different stages: before the training, after the training and four months later. Brain connections in individuals trained with the method of loci resembled those found in the athletes, both immediately after the training and four months later. Two regions seemed specially important, acting as “hubs of connectivity”: the medial prefrontal cortex (MPFC) and the right dorsolateral prefrontal cortex (DLPFC).

The MPFC is known to be involved in memory consolidation, as well as in relating new memories with pre-existing ones. The DLPFC, on the other hand, has a role in planning, abstract reasoning and learning strategically. Interestingly, the more the patterns of connections in the volunteers resembled those of the athletes, the better their performance was.

Despite the crucial role of the MPFC and DLPFC, the authors stressed that the most important changes following the training were those regarding connections between brain regions, rather than focal changes in specific areas. In other words, what the training does is re-shaping the connections to make them more efficient.

Some believe that mnemonic techniques work so well because they “hijack” everyday mental mechanisms that have been subjected to strong evolutionary pressure, such as seeing objects and not bumping into them, or being able to run away from them if we perceived them as dangerous. Also, for obvious survival reasons, we also easily remember things that have a strong emotional content, such as events or behaviours that made us extremely happy or terribly sad. The method of loci uses these skills to retrieve memories, a beautiful example of how versatile our brains can be.

In the legend of Simonides, the poet is saved because two young men called him out of the room just before the roof fell off. According to Cicero, those men were twin brothers Castor and Pollux, sons of Leda. Simonides had just chanted a poem to honour the host which included a long passage about the twins. That did not go down well with the host, who decided he would only pay Simonides half the fee agreed, adding that he could ask the twins for the other half, as they featured so prominently in the poem. I suppose you could say the twins gave him a lesson we will never forget.


  1. Dresler et al. (2017) Mnemonic Training Reshapes Brain Networks to Support Superior Memory Neuron 93:1227–1235 doi: 10.1016/j.neuron.2017.02.003

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