Researchers now understood how the brain ages better
Now researchers say that data from high-resolution functional brain imaging can be used to show some of the underlying causes for differences in memory proficiency between older and younger adults.
Researcher, Zachariah Reagh, of the University of California, Davis, said: “At the fundamental level, we still understand very little about how ageing affects the neural systems that give rise to memory.”
The study, published in the journal Neuron, involved 20 young adults, aged 18 to 31, and 20 cognitively healthy older adults, aged 64 to 89. It sheds light on dementia’s effects, too.
They were asked to perform two kinds of tasks in an fMRI scanner, an object memory task and a location memory task.
Dr Reagh said that because fMRI looks at the dynamics of blood flow in the brain, it enables researchers to determine which parts of their brains the subjects are using in each task.
Learning more about ageing shows more clearly the effect of dementia
These findings suggest that the brain ageing process is selective. Our findings are not a reflection of general brain ageing, but rather specific neural changes that are linked to specific problems in object but not spatial memory.
In the object task, participants learned pictures of everyday objects and were then asked to distinguish them from new pictures.
Study senior author Doctor Michael Yassa, Director of the Centre for the Neurobiology of Learning and Memory at the University of California, Irvine, said: “Some of the pictures were identical to ones they’ve seen before, some were brand new, and others were similar to what they’ve seen before – we may change the colour or the size.
“We call these tricky items the ‘lures. And we found that older adults struggle with these lures.
“They are much more likely than younger adults to think they’ve seen those lures before.”
The second task was similar but required subjects to determine during test whether objects changed their location. For this type of memory task, older adults fared quite a bit better.
Scientists used brain imaging to consider ageing’s effects on brain function
Dr Reagh said: “This suggests that not all memory changes equally with ageing. Object memory is far more vulnerable than spatial memory, at least in the early stages.”
He said other studies have shown that problems with spatial memory and navigation do manifest as people go down the path to Alzheimer’s disease.
But by scanning the subjects’ brains while they underwent the tests, the researchers were able to establish a mechanism within the brain for that deficit in object memory.
They found that it was linked to a loss of signaling in the part of the brain called the anterolateral entorhinal cortex.
This area was already known to mediate the communication between the hippocampus, where information is first encoded, and the rest of the neocortex, which plays a role in long-term storage.
It is also an area that is known to be severely affected in people with Alzheimer’s disease.
Dr Yassa said: “The loss of fMRI signal means there is less blood flow to the region, but we believe the underlying basis for this loss has to do with the fact that the structural integrity of that region of the brain is changing.
“One of the things we know about Alzheimer’s disease is that this region of the brain is one of the very first to exhibit a key hallmark of the disease, deposition of neurofibrillary tangles.”
But the researchers didn’t find age-related differences in another area of the brain connected to memory, the posteromedial entorhinal cortex.
They showed that this region plays a role in spatial memory, which was also not significantly impaired in the older subjects.
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Dr Yassa said: “These findings suggest that the brain ageing process is selective. Our findings are not a reflection of general brain ageing, but rather specific neural changes that are linked to specific problems in object but not spatial memory.”
To determine whether this type of fMRI scan could eventually be used as a tool for early diagnosis, the researchers plan to expand their work to a sample of 150 older adults who will be followed over time.
They will also be conducting PET scans to look for amyloid and tau pathology in their brains as they age.
Dr Yassa said: “We hope this comprehensive imaging and cognitive testing will enable us to figure out whether the deficits we saw in the current study are indicative of what is later to come in some of these individuals.”
Dr Reagh added: “Our results, as well as similar results from other labs, point to a need for carefully designed tasks and paradigms that can reveal different functions in key areas of the brain and different vulnerabilities to the ageing process.”