What happens in the brain when you learn a mnemonic?

This is part of a series exploring the brains behind exceptional memory: to what extent is it natural and learnt? How fast can a complete novice pick up a mnemonic? Can memory training help those suffering from memory impairment and depression? Finally, what’s going on in the brain as one masters the method of loci? 

Decades of research show that targeted training can improve one’s memory.One popular mnemonic is the method of loci (also known as the memory palace), in which you place to-be-remembered items along an imaginary route and mentally re-walk the route to retrieve the memory.  Extensive training in the method dramatically enhances recall in both young and old adults, suggesting that even later in life the human brain retains enough “cognitive reserve” to master the task. This reserve is thought to come from optimizing existing neural pathways or incorporating new pathways into the computation.

As you might have guessed, the elderly lag behind on memory performance compared to younger adults; what’s surprising is that this age-related difference often increases with training. What's going on?

A small Swedish study in 2003 sought to answer these questions. They recruited 8 volunteers in their mid-twenties and 16 volunteers in their late sixties and used PET scans to follow changes in their brain activity as they adopted the mnemonic. After obtaining a baseline for memory performance and brain activity, researchers gave the participants a long list of loci to remember while scanning their brains. This diverges from the standard method, which encourages memory trainees to find loci of personal significance. However, a given set of routes minimizes any variation that may stem from building individualistic memory palaces, such as how easy they are to remember and navigate and how much “storage capacity” they possess. Once the participants could confidently recall the loci, they were instructed to use them to store 18 unrelated words.

The training was intense and difficult, but it largely paid off. All of the young volunteers showed an improvement in recall, remembering on average 5.12 more words than their initial performance. Results for the elderly dramatically diverged: 8 participants showed on average a gain of 3.75 more remember words, while the other 8 performed worse than before. When researchers pooled the data together, training magnified the age-related difference in memory performance, similar to results from previous studies.

Researchers turned to brain scan data for clues. Only those who improved showed increased activity in the occipito-parietal cortex and left retroplenial cortex, brain regions associated with spatial mental visualization. In fact, a similar pattern of activation occurs in memory masters as they spontaneously use the method of loci, suggesting it reflects the use of the method rather than a neural quirk only seen in those with superior memory.

A slew of cognitive tests showed that the older participants did not differ in their educational levels, vocabulary or cognitive reserve capacity – in this case, the mental power to enhance their performance after learning a mnemonic. The reason behind their lack of improvement – uncovered by the researchers in an informal chat afterwards – was that they simply didn’t use the method for word encoding! Many older participants found it difficult to associate the loci and the words under the experiment’s tight time constraints, and gave up. This subjective experience correlated with brain scan data, which showed that as a group the older participants had less activation of areas of the frontal lobe, which are hypothesized to support working memory processes such as organization and generating words from images.

While somewhat anti-climatic, this is good news: despite a significant drop in processing power with aging, we may still be able to benefit from the mnemonic. It would be interesting to see if, by using an easier training protocol, the non-learners might enjoy a similar boost in memory  (albeit small) as their age-matched peers.

In fact, with some tinkering around, several groups of psychologists have modernized the learning of the method of loci. Think virtual reality.


Superior memory and superior intelligence: is there a link?
As a population we often associates superior memory with cleverness, but is there actually a link?
Unfortunately, data on the IQ of memory masters is embarrassingly meager. A study in 2002 profiled general cognitive abilities of 10 superior memorizers and found no difference compared to their matched controls. This suggests that learned superior memory doesn’t transfer to other cognitive domains, such as logic, communication, planning and fluid problem solving. The psychologist K Anders Ericsson famously believes that expertise in any domain results from deliberate practice. On the other hand, depending on your definition of “intelligence”, superior memory obviously contributes to speedier learning and longer retention. According to Boris Conrad, a former World Memory Champion turned neuroscientist, IQ affects the rate of learning mnemonics and the ultimate level of memory performance attainable, just like any other domain. While it’s true that many learned memory experts have high IQ, it’s hard to tease out if this is simply because intelligent people often enjoy challenging themselves in cognitive tasks.
Perhaps it’s more interesting to ask whether natural memory superiority is dependent on IQ. Here the water becomes even murkier: cases of superior memory in otherwise learning-impaired individuals suggest that memory and IQ are separate entities. People with Highly Superior Autobiographical Memory (HSAM) further support that memory and IQ can be separated. HSAM individuals are able to recall their past in exquisite detail, yet perform normally on IQ tests and non-autobiographical memory tasks, such as remembering lists of items. However, the underlying reason for such unusual memory is poorly understood and these observations are difficult to generalize.
In the end, one thing is clear: natural superior memory is often confined to a type of memory, such as autobiographical or abstract, while superior memory learned through training seems to have a more general impact on cognition, perhaps as a result of applying the same technique to different materials. In both cases, the link to intelligence is rather tenuous.

Nyberg L, Sandblom J, Jones S, Neely AS, Petersson KM, Ingvar M, & Bäckman L (2003). Neural correlates of training-related memory improvement in adulthood and aging. Proceedings of the National Academy of Sciences of the United States of America, 100 (23), 13728-33 PMID: 14597711