A team from the University of California, Irvine, has discovered that high-resolution functional magnetic resonance imaging (fMRI) of the brain can be used to show some of the underlying causes of differences in memory proficiency between older and younger adults.
For the study, the researchers asked 20 cognitively healthy adults between 18 and 31 years old and 20 between 64 and 89 years old to perform an object memory task and a location memory task while undergoing fMRI scanning to determine which parts of the brain the subjects were using for each activity.
For the first task, participants viewed pictures of everyday objects and were asked to distinguish them from new pictures.
“Some of the images were identical to ones they’d seen before, some were brand-new and others were similar to ones they’d seen earlier— we may have changed the color or the size,” Michael Yassa, director of UCI’s Center for the Neurobiology of Learning & Memory and the study’s senior author, said in a statement. “We call these tricky items the ‘lures.’ And we found that older adults struggle with them. They’re much more likely than younger adults to think they’ve seen those lures before.”
The participants were asked to determine in the second task whether the location of objects had been altered. The older participants fared better in this task.
“This suggests that not all memory changes equally with aging,” lead author Zachariah Reagh, who participated in the study as a graduate student at UCI and is now a postdoctoral fellow at UC Davis, said in a statement. “Object memory is far more vulnerable than spatial, or location, memory— at least in the early stages.”
The researchers were able to establish a cerebral mechanism for the deficit in object memory and found that it was linked to a loss of signaling in the anterolateral entorhinal cortex, which is known to mediate communication between the hippocampus and the rest of the neocortex. The anterolateral entorhinal cortex is also an area of the brain severely affected in Alzheimer’s patients.
“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 part of the brain is changing,” Yassa said. “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.”
However, the team did not find age related differences in the posteromedial entorhinal cortex, suggesting that this region plays a role in spatial memory.
“This suggests that the brain aging process is selective,” Yassa said. “Our findings are not a reflection of general brain aging but rather of specific neural changes that are linked to specific problems in object but not spatial memory.”
The researchers will now expand the study to a sample of 150 older adults who will be followed over time. The team will also conduct positron emission tomography scans to look for amyloid and tau pathology in their brains as they age.