Is memory improving in old age?

I am at that weird age when your memory leads to contradictory experiences. On the one hand, I am old enough to experience more and more lapses of memory which makes me wonder if I have early stages of dementia. On the other hand, I sometimes get told by friends and acquaintances that they are impressed by how much stuff I know and wonder how I can remember all these things. So, what is it?

I dug into the science of memory and came across a fascinating review article from 2022 that seems to summarise a lot of our current knowledge on how memory works and how it changes with age. Obviously, I am not a specialist in this topic, but I figure I might share the insights I gained from this article with you since memory is an important ingredient to being successful in most careers.

As an investment strategist, I must remember all kinds of data like the valuation of markets and stocks or the most recent drivers of market performance, the actions and intentions of central bankers, the latest developments on the inflation and economic growth front, etc. On top of that, I must remember who my clients are, what they do, what they are interested in, etc.

Plus, I must remember a good chunk of financial history that I can fall back on when markets do strange things and panic (which inevitably they do from time to time). In a crisis, often the only thing you can rely on is historic precedent to make a quick and dirty analysis of how things may evolve since fundamentals and rational thought have been furloughed in these episodes.

Oh, and finally, I need to remember what I wrote in earlier notes and posts like this one. Believe me, knowing what you said yesterday is quite important if you don’t want to embarrass yourself in public. But this gets harder and harder over time. According to my substack archive, I have written more than 1,300 of these posts since 2019, not counting the ones I wrote for a previous employer that have disappeared to computer nirvana. On top of that, I write dozens of in-depth analyses a year for my employer.

I am sure, you can come up with a similarly long list of things you need to remember to perform your job.

So, what do scientists have to say about memory and old age? Or rather, what does this one overview article say about memory and old age?

First, memory does indeed get worse with age. As we grow older, we forget more and more things. The way to show this is to give people a random set of 12 items to remember. But each word in the sequence has a different value from 1 to 12 points randomly assigned to the words. Thus, one has to remember not only the words but the random value associated with them and then mentally sort these words from highest to lowest value. The chart below shows that the recall of high-value words is about the same in older and younger people, but younger people are much better at remembering lower-value words.

Recall in selectivity task

Source: Knowlton and Castel (2022)

Ok, we can’t remember as many things as we used to when we get older, but we older people have a distinct advantage over the young. We have experience. And experience and practice teach us which bits of information are important and which ones are not.

In the lab experiment above, one can see that when it comes to the really important words with high values, old people were just as good as younger people at remembering them.

In real life, we are constantly bombarded with too much information, most of which is low value and irrelevant to the task at hand. And one way to succeed in such an information overload world is to be selective in remembering information. People who know through experience which information matters and which one doesn’t can focus on remembering the important bits. People with less experience can remember a lot more information, but their memory is cluttered with less important things or distracted by noise.

In the recall experiment shown above, one can calculate a selectivity index for each participant that measures how selectively a person recalls the high value items and compares this recall with pure chance. The selectivity index is then scaled so that a reading of +1 indicates perfectly selective memory where a person only remembers the most valuable items on the list and none of the lower value items. Similarly, a selectivity index of -1 indicates a person who only remembers the unimportant low value noise and not the information, while a selectivity index of 0 indicates that recall is essentially random.

The second chart today shows the proportion of words recalled together with the selectivity index by age group. Also, children with ADHD and older people with Alzheimer’s Disease are marked in the chart with asterisks.

Recall and selectivity by age group

Source: Knowlton and Castel (2022)

This is the chart that I have printed, framed, and put next to my bedside. First, it shows that as we get older, we have more focused recall. The selectivity index rises throughout most of adulthood peaking for people who are aged around 65. Meanwhile, the proportion of words recalled drops from young adulthood onward. This increased selectivity is what lets older adults keep up with the younger ones in memory and recall tasks and is the reason why it is unwise of businesses to let older employees go and focus on the young blood instead. Businesses need a mix of young blood with all its energy and good memory and older people with the experience to know which information is useful and which one isn’t.

But the chart also shows why people with Alzheimer’s Disease and ADHD have difficulty in life. Alzheimer’s Disease kills both recall and selectivity. People don’t just forget stuff they forget the important stuff.

This is why it is so hard to watch loved ones suffer from Alzheimer’s. As the latest commercial by the Alzheimer Society says, they die several times. They die when they can’t remember a recipe anymore, then again when they don’t remember past events from their lives, then again when they forget the names of their children, etc. It is heartbreaking.

ADHD, meanwhile, is different. Children with ADHD have similar recall as healthy children. It’s just that they cannot differentiate between the important and the unimportant stuff. Their selectivity is pretty much the same as randomly remembering stuff without context. In other words, their mind is constantly cluttered, and it is hard to work effectively if you have a hard time differentiating between what matters and what doesn’t.