It’s always the keys, the first thing we leave somewhere … but can’t remember where exactly.
And it’s beautifully symbolic.
At a certain age, the keys keep falling out of your head, making a hole for everything else in your memory to fall out.
But a new study suggests that our memory declines over time, not via a series of holes, but more as a blurring at the edges.
What emerges, the researchers say, is a more nuanced understanding of how our memory holds itself together as we age.
How did they do it?
For Dr Zachariah Reagh, assistant professor of psychological and brain sciences in Arts & Sciences at Washington University in St Louis – and corresponding author of the study – the starting point was to abandon the quiz-like format of regular memory tests for cognitive decline.
(Donald Trump did a spectacular job recognising an elephant in such a test recently.)
Instead of asking a group of old people “to recite a group of words or remember a string of numbers,” Dr Reagh wanted to take a “naturalistic approach, one that more closely resembled real-world activities.”
Going to the movies. Is that it?
Dr Reagh used a collection of data from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) that included functional MRI (fMRI) scans of people watching a shortened version of the Alfred Hitchcock film, Bang! You’re Dead.
The data came from people aged 18 to 88.
“There were no specific instructions, or a ‘gotcha’ moment,” said Dr Reagh, in a prepared statement. “They just got to kick back, relax and enjoy the film.”
While the participants were kicking back, the fMRI scans showed their brains were “hard at work recognising, interpreting and categorising events in the movies”.
What were the researchers looking for?
One particular way our brains categorise events is by marking boundaries – when the event has ended and a new event has started.
For the brain an “event” is anything in the real world that is being perceived and processed. It can be an entire conversation, or “a component of it, for example”, Dr Reagh said.
“We take these meaningful pieces and extract them out of a continuous stream.”
And what constitutes a boundary is actually consistent among people.
“If you and I watch the same movie, and we are given the instruction to press a button when we feel one meaningful unit has ended, you and I will be much more similar in our responses than we are different,” Dr Reagh said.
These boundary events – when the brain recognises that one thing has finished and another has started – were the focus of the investigation.
As the authors of the paper laid out there reasoning, somewhat elegantly: “The process of parsing a continuous stream of information into meaningful chunks – event segmentation – is thought to be a fundamental process that influences event comprehension, episodic memory retrieval and prediction.”
In other words, the brain neatly bundles information into events that we can understand, that we can later recall, and that we can use to make predictions about what’s going to happen next.
Hence, the ability for a person’s brain to create meaningful chunks correlates with the person’s “ability to later remember information, suggesting that event boundaries play a powerful role in organising information in memory”.
What the researchers were looking for was how these boundary events were processed in the brains of their young, middle-aged and old participants.
Different parts of the brain lit up, depending on age
In the fMRI results, as the brain processed the boundaries of events – where one thing was turning into another – the older adults showed similarly increased activity as the youngsters.
Some of this shared increased activity occurred in the hippocampus across all age groups – the hippocampus being a key part of the limbic system, where motivation, emotion, learning and memory are regulated.
Where activity was lower for the older participants was an area of the brain known as the posterior medial network – regions in the midline and toward the backside of the brain that are “heavily involved in representing context and situational awareness”.
However, this appears to be offset by increased activity in the medial prefrontal cortex, at the front of the brain – an area “implicated in broad, schematic knowledge”.
Dr Reagh gives the example of older brains recognising what it’s like to go to a grocery store as opposed to a particular grocery store.
So what’s the gist?
The researchers make an interesting guess as to what’s happening as we get older: “What might be happening is as older adults lose some responsiveness in posterior parts of the brain, they may be shifting away from the more detailed contextual information.”
Instead, as activity levels heighten in the front of the brain, “things might become more schematic. More ‘gist-like’”.
He said that overall activity declined “pretty reliably” across ages 18 to 88, he said.
When grouped into “younger, middle aged, and older” groups, he said there was a statistically reliable drop in activity from one group to another.
“Older adults might be representing events in different ways, and transitions might be picked up differently than, say, a 20-year-old,” Dr Reagh said.
“An interesting conclusion one could draw is maybe healthy older adults aren’t ‘missing the picture’. It’s not that the info isn’t getting in, it’s just it’s getting in differently … In some areas, activity goes down and, in some, it actually goes up.”