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Can a Mnemonic Slow Age-Based Memory Loss?

The views expressed are those of the author and are not necessarily those of Scientific American.


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One of the tragedies of aging is the slow but steady decline in memory. Phone numbers slipping your mind? Forgetting crucial items on your grocery list? Opening the door but can’t remember why? Up to 50 percent of adults aged 64 years or older report memory complaints. For many of us, senile moments are the result of normal changes in brain structure and function instead of a sign of dementia, and will inevitably haunt us all.

Rather than taking it lying down, scientists are devising interventions to help keep the elderly mind sharp. One popular approach—borrowed from the training of memory experts—is to teach the elderly mnemonics, or little tricks to help encode and recall new information using rhythm, imagery or spatial navigation.

By far the most widely used mnemonic device is the method of loci (MoL), a technique devised in ancient Greece. In a 2002 study looking at the neural correlates of superior human memory, nine of 10 memory masters employed the method spontaneously. It involves picturing highly familiar routes through a building (your childhood home) or a town (your way to work). Walk down the route and imagine placing to-be-remembered items at attention-grabbing spots along the way; the more surreal or bizarre you make these images, the better they can help you remember. To recall these stored items, simply retrace your steps. Like fishing lines, the loci are hooked to the memory and help you pull them to the surface. Although generally used to remember objects, numbers or names, the MoL has also been used in people with depression to successfully store bits and pieces of happy autobiographical memories that they can easily retrieve in times of stress.

However, with age the brain gradually loses the flexibility to change in response to training. Despite mental wear-and-tear, many studies show that MoL successfully slows memory decline in the normal aging population, but why this happens is a complete mystery. That is, until recently.

Thickening of the Brain

In 2010 a Norwegian team set out to look for the most obvious sign of MoL-induced neuroplasticity: macro-structural changes in the brain. Expert instructors led 23 volunteers with an average age of 61 through an intensive eight-week long program. These volunteers managed to use MoL to remember three lists of 30 words in sequential order in no more than 10 minutes, a remarkable feat of memory! The control group – matched in age, sex and education- were instructed to “live as usual” for the eight weeks. During the final test, researchers challenged both groups with this task: they first flashed a list of 15 unrelated words, each for only a second, and asked the volunteers to remember the words and their sequential order. Researchers then showed them a list of 30 words — 15 previously presented and 15 new — and asked both groups to not only pick out the matching words but also to identify their position in the first list. The second task involves spatial recognition and should particularly benefit from MoL training.

Just as the researchers thought, MoL-trained volunteers correctly named the position of six more words on average, than did the volunteers who were not trained although they recognized a similar number of matched words as the controls. Structural MRI images taken before and after training identified a surprisingly large morphological change in the MoL-trained volunteers. These individuals showed significant thickening of the right fusiform cortex and the right orbitofrontal cortex, areas particularly involved in encoding abstract visual memory. The bigger the change in an individual, the greater the improvement in his or her memory performance.

The control group, on the other hand, showed a trend towards thinning of their cortices over the eight weeks perhaps as a reflection of cortical atrophy in normal aging. Similarly, a later study showed that learning MoL increased the integrity of elderly participant’s white matter compared to controls. White matter is made up of the myelinated axons of neurons that connect different brain regions and provides highways for communication between those regions.

This initial sleuthing reveals remarkable adaptability of the elderly brain as it learns to process verbal information using spatial imagery. While intriguing, these studies only just scratched the surface: the volunteers were self-selected through answering a newspaper ad, and the small sample size cautions against generalization. Furthermore, these changes may reflect a general increase in cognitive load, rather than the use of MoL per se. But compared to other mnemonics, the benefits of MoL often persist after initial training even without subsequent practice, so researchers wondered whether these structural changes might underlie the method’s long-term benefits.

Rewiring the Brain

Inferring functional and behavioral changes from structure alone is quite the difficult leap, if not downright impossible. Two groups of researchers decided to determine whether learning MoL alters brain activity patterns instead. In one small study in 2003 scientists in Sweden recruited young volunteers in their twenties and elderly participants in their sixties and used PET scans to follow changes in their brain activity as they adopted MoL to remember a list of random words. Several mentally-grueling sessions later, all of the younger volunteers – but only half of the elderly – remembered roughly four more words than they had in their initial test, with the younger crowd performing much better.

Those who improved showed increased activity in the occipito-parietal cortex and left retroplenial cortex during encoding. These brain regions are associated with spatial mental visualization and navigation. A similar pattern of activation was previously found in memory champions as they spontaneously use the MoL. This suggests that these changes were due to the volunteers adopting the mnemonic, and that despite old age, the brain is still capable of a qualitative shift in the way it encodes new memories. A later study using fMRI confirmed these results, and further implicated fusiform and lingual gyri in memory encoding.

But wait, what about the half of elderly participants who didn’t improve? One important clue was their complete lack of activation of MoL-associated brain regions during testing, prompting researchers to wonder whether if these volunteer actually used the MoL. As it turned out, they didn’t! A subsequent informal chat revealed that many older participants found it difficult to associate the loci with the words under the experiment’s tight time constraints, felt frustrated and gave up.

So although a promising technique for many, MoL training is difficult, particularly for the elderly who are less able to generate and rely on a mental map of distinctive landmarks. Is there any way to lower the barrier of entry for learning MoL?

Modernizing the Mnemonic

In early 2012, a team of Canadian researchers gave the ancient MoL mnemonic a 21st century facelift. Inspired by the first-person shooter Half-life 2, the team constructed several detailed virtual reality environments to serve as loci, rather than letting MoL-learners generate their own. This technique deviated from the 1000-year rule that the loci need to be of personal significance for the method to work.

But it paid off. Researchers allowed 142 undergraduate volunteers only five minutes to familiarize themselves with the virtual environment before giving two thirds of them instructions in using the MoL to memorize 110 unrelated words. Some were told to pick a familiar environment, while others were allowed to use the virtual environment they just navigated. The other third didn’t receive any specific instructions on memory techniques.

Both MoL groups outperformed the controls. They were 10 to 16 percent more accurate in their recall, and students who used the virtual environment performed just as well as those told to generate their own landmarks. But here’s the interesting bit: in both groups, participants reported that they didn’t always follow instructions, instead sometimes using methods other than MoL to remember the words. But compared to participants in the standard MoL group, those using the virtual environment took to the mnemonic more readily. On average, they invoked the visual landmarks more often as they memorized the word list.

Extrapolating data from young adults to the aging population warrants caution, but researchers are optimistic. By using software that creates many diverse environments, the elderly may be able to tailor the richness and theme of each space to both their learning ability and to what they wish to remember. A young scientist from Belgium is dreaming big: in a recent TED talk, Kasper Bormans described using a virtual reality replica of their home to help patients with Alzheimer’s disease “store” the memory of their loved one’s faces using the MoL. By combining the mnemonic with training in other cognitive domains – logic and reasoning, organization and attention – as well as anti-dementia medication where needed, researchers hope to slow (if not halt) the loss of memory we experience as we age.

References:

Engvig A et al. (2010) Effects of memory training on cortical thickness in the elderly. NeuroImage 52: 1667–1676.

Engvig A et al. (2012) Memory training impacts short-term changes in aging white matter: a longitudinal diffusion tensor imaging study. Hum Brain Mapp ; 33(10): 2390-406. doi: 10.1002/hbm.21370

Nyberg L et al. (2003).Neural correlates of training-related memory improvement in adulthood and aging. PNAS 100 (23), 13728-33 PMID: 14597711

Legge EL et al. (2012) Building a memory palace in minutes: equivalent memory performance using virtual versus conventional environments with the Method of Loci .Acta Psychol (Amst). 141(3):380-90

Image(s):

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Shelly Fan About the Author: Shelly Xuelai Fan is a PhD Candidate in Neuroscience at the University of British Columbia, where she studies protein degradation in neurodegenerative diseases. She is an aspiring science writer with an insatiable obsession with the brain. She mulls over neuroscience, microbiomes and nutrition over at Neurorexia. Follow on Twitter @ShellyFan.

The views expressed are those of the author and are not necessarily those of Scientific American.






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