Even among healthy people, a faltering memory is often an expected part of aging—but it’s not inevitable.
“Some individuals exhibit remarkable maintenance of memory function
throughout late adulthood, whereas others experience significant memory
decline. Studying these differences across individuals is critical for
understanding the complexities of brain aging, including how to promote
resilience and longevity,” said Alexandra Trelle, a postdoctoral
research fellow at Stanford University.
Building on studies that have focused on young populations, Trelle
and colleagues are investigating memory recall in healthy, older adults
as part of the Stanford Aging and Memory Study. In new research,
published May 29 in
eLife, this team has found that memory recall
processes in the brains of older adults can look very similar to those
previously observed in the brains of young adults. However, for those
seniors who had more trouble remembering, evidence for these processes
was noticeably diminished.
By gaining a better understanding of memory function in older adults,
these researchers hope to someday enable earlier and more precise
predictions of when memory failures signal increased risk for dementia.
A striking similarity
When Anthony Wagner, the Lucie Stern Professor in the Social Sciences at Stanford’s School of Humanities and Sciences, was a
graduate student
at Stanford in the ’90s, he conducted some of the first fMRI studies of
memory formation. At that time, state-of-the-art imaging and analysis
technologies only allowed measurement of the magnitude of activity from a
centimeter-and-a-half section of the brain.
In contrast, the current study measured activity from the whole brain
at high-resolution, and analyses not only focused on the magnitude of
activity but also on the memory information that is contained in
patterns of brain activity.
“It’s exciting to have basic science tools that allow us to witness
when a memory is being replayed in an individual mind and to draw on
these neural processes to explain why some older adults remember better
than others,” said Wagner, who is senior author of the paper. “As a
graduate student, I would never have predicted that we would do this
kind of science someday.”
In the experiment, 100 participants between the ages of 60 and 82 had
their brains scanned as they studied words paired with pictures of
famous people and places. Then, during a scanned memory test, they were
prompted with words they had seen and asked to recall the associated
picture. The memory test was designed to assess one’s ability to
remember specific associations between elements of an event, a form of
memory that is often disproportionately affected by aging.
In the scans, the researchers observed that the brain processes that
support remembering in older adults resemble those in younger
populations: when people remember, there is an increase in hippocampal
activity—a brain structure long known to be important for remembering
events—along with the reinstatement of activity patterns in the cortex
that were present when the event was initially experienced. That is,
remembering entails neural time travel, replaying patterns that were
previously established in the brain.
“It was striking that we were able to replicate this moment-to-moment
relationship between hippocampal activity, replay in the cortex, and
memory recall, which has previously been observed only in healthy
younger adults,” said Trelle, who is lead author of the paper. “In fact,
we could predict whether or not an individual would remember at a given
moment in time based on the information carried in patterns of brain
activity.”
The researchers found that, on average, recall ability declined with
age. Critically, however, regardless of one’s age, stronger hippocampal
activity and replay in the cortex was linked to better memory
performance. This was true not only for the memory test conducted during
the scan but also memory tests administered on a different day of the
study. This intriguing finding suggests that fMRI measures of brain
activity during
memory recall are tapping into stable differences across individuals, and may provide a window into brain health.
Only the beginning
This research lays the foundation for many future investigations of memory in
older adults
in the Stanford Aging and Memory Study cohort. These will include work
to further detail the process of memory creation and recall, studies of
change in memory performance over time, and research that pairs fMRI
studies with other kinds of health data, such as changes in brain
structure and the build-up of proteins in the brain that are linked to
Alzheimer’s disease.
The ultimate aim is to develop new and sensitive tools to identify
individuals who are at increased risk for Alzheimer’s disease before
significant
memory decline occurs.
“We’re beginning to ask whether individual differences in the ability
to mentally travel back in time can be explained by asymptomatic
disease that impacts the
brain
and predicts future clinical diagnosis,” said Wagner. “We’re hopeful
that our work, which requires rich collaborations across disciplines,
will inform clinical problems and advance human health.”
More information:
Alexandra N Trelle et al, Hippocampal and cortical mechanisms at
retrieval explain variability in episodic remembering in older adults,
eLife (2020).
DOI: 10.7554/eLife.55335
