When I was a child, I vividly remember a very funny episode with my Grandpa. He couldn’t find his glasses – yet there they were, perched on the top of his head. I thought he was just playing along, but I gradually realised that he was being serious. It still makes me chuckle to this day, although memory loss isn’t really anything to smile at.
“Senior moments”, or those little memory lapses that become more frequent with age, are rather annoying. As we get older, we might forget where we parked our car, or whether we turned the stove off or not. Sometimes, we might even call our children by the wrong names. But currently there are no good ways to differentiate between memory lapses that constitute a normal part of ageing, and those which may signal the early stages of a severe disorder such as Alzheimer’s disease.
In a study published on March 7 in the journal Neuron, researchers report 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.
“At the fundamental level, we still understand very little about how ageing affects the neural systems that give rise to memory,” says Zachariah Reagh, the study’s first author, a postdoctoral fellow at the University of California, Davis.
The paper reports data from 20 young adults (ages 18 to 31) and 20 cognitively healthy older adults (ages 64 to 89). Participants were required to perform two kinds of tasks in an fMRI scanner: an object memory task and a location memory task. fMRI measures the dynamics of blood flow in the brain, thus enabling the investigators to determine which parts of their brains the subjects are using in each task.
Object Memory Task
In this task, the participants learned pictures of everyday objects and were then asked to distinguish them from new pictures.
According to Michael Yassa, Director of the Centre for the Neurobiology of Learning and Memory at the University of California, Irvine, and the study’s senior author,
“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.”
Location Memory Task
For the second task, subjects were required to determine whether the objects had changed their location. For this type of memory task, older adults fared quite a bit better.
“This suggests that not all memory changes equally with ageing,” said Reagh. “Object memory is far more vulnerable than spatial memory, at least in the early stages.”
Other studies have revealed that issues with spatial memory and navigation do occur as individuals go down the path to Alzheimer’s disease.
By scanning the subjects’ brains while they underwent these tests, 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 signalling in the part of the brain called the anterolateral entorhinal cortex.
It was already known that this area mediates 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.
“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,” Yassa explained. “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.”
The researchers did not find age-related differences in another area of the brain connected to memory, the posteromedial entorhinal cortex. Evidently, this region plays a role in spatial memory, which was also not significantly impaired in the older subjects.
“These findings suggest that the brain ageing process is selective,” Yassa added. “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 order to discern whether this type of fMRI scan could potentially be used as a tool for early diagnosis of Alzheimer’s, the researchers plan on expanding their work to a sample of 150 older adults who will be followed over time. Yassa and colleagues will also conduct PET scans to look for amyloid and tau pathology in their brains as they age.
“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,” said Yassa.
“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,” concluded Reagh.