Memory
loss in older adults
due to distractions,
not inability to focus
fMRI
study confirms brain changes with aging, provides new diagnostic
tool
Berkeley --
The short-term memory problems that accompany normal aging are
associated with an inability to filter out surrounding distractions,
not problems with focusing attention, according to a study by
researchers at the University of California, Berkeley.
Although
older patients often report difficulty tuning out distractions, this
is the first hard evidence from functional magnetic resonance
imaging (fMRI) studies of the brain that memory failure owes more to
interference from irrelevant information than to an inability to
focus on relevant information.
"Difficulty
filtering out distractions impacts a wide range of daily life
activities, such as driving, social interactions and reading, and
can greatly affect quality of life," said study leader Dr. Adam
Gazzaley, adjunct assistant professor of neuroscience at UC Berkeley
and a newly appointed assistant professor of neurology and
physiology at UC San Francisco.
"These
results reveal that efficiently focusing on relevant information is
not enough to ensure successful memory," he said. "It is also
necessary to filter distractions. Otherwise, our capacity-limited
short-term memory system will be overloaded."
The finding
could mean that an inability to ignore distracting information is at
the heart of many cognitive problems accompanying aging, Gazzaley
said, and suggests that drugs targeting that problem may be more
effective at improving memory than drugs that improve focusing
ability. He now is exploring the therapeutic role of different
medications - including one of the main drugs to treat Alzheimer's
disease - in older individuals with suppression deficits.
Because
Gazzaley and his colleagues have identified areas of the brain that
are markers for focusing and ignoring visual information, fMRI may
be a good tool for assessing the value of therapies designed to
improve memory and for diagnosing attention and memory problems in
young and old, ranging from attention deficit disorder to dementia.
"Is this a
unifying mechanism that can account for broader problems regarding
attention and memory?" asked coauthor Dr. Mark D'Esposito, UC
Berkeley professor of neuroscience and psychology and director of
the campus's Henry Wheeler Brain Imaging Center. "I think it
explains a lot of it. If you are unable to block out distracting
information, you can't really attend to what you are supposed to
attend to, you can't get in what you are supposed to remember, and
you have a hard time retrieving what you are supposed to remember.
Rather than think of it as someone having an attention problem and a
memory problem, you can just think of it as someone having one
problem - the inability to filter out distracting information -
that's affecting other domains such as attention and memory."
Gazzaley,
D'Esposito, research assistant Jeffrey W. Cooney and graduate
student Jesse Rissman will report their findings in the journal
Nature Neuroscience, to be published online Sept. 11.
Gazzaley
and his colleagues compared young adults aged 19 to 30 with older
adults aged 60 to 77 using a simple memory test that introduced
irrelevant information. The tests were conducted while subjects'
heads were inside a fMRI scanner so that activity in the brain could
be pinpointed.
While young
subjects were easily able to suppress brain activity in areas that
process information irrelevant to the memory task, older adults on
average were unable to suppress such distracting information. Both
groups were equally able to enhance brain activity in the areas
dealing with information relevant to the task.
Interestingly, six of the 16 older adults had well-preserved
short-term memory and no problems ignoring irrelevant information,
suggesting that some people are able to avoid memory loss as they
age. Gazzaley hopes to find out what makes these people different
from the average aging adult.
"Encouragingly, a subgroup of the older population does not
experience this suppression deficit and accompanying memory
impairment, opening the road for studies of successful aging,"
Gazzaley said.
Gazzaley, a
neurologist who specializes in treating mild cognitive impairment
common in older adults, set out to see how attention affects short
term or "working" memory. He developed a test to distinguish two
aspects of attention: the brain's ability to focus on a visual
stimulus, and the ability to suppress or ignore other visual
information. He noted that both involve brain activity in the higher
level neocortex, acting on the visual cortex - a process he refers
to as "top-down modulation."
The test
involves presenting a sequence of four images, two of them faces and
two natural scenes. Subjects were asked to remember either faces, in
which case the scenes were irrelevant information; or scenes, in
which case faces were irrelevant. Subjects then were asked whether a
particular face or scene appeared among the four images. In a
separate test, subjects were asked only to observe the stimuli
without attempting to remember them.
After first
identifying with the fMRI the regions in the brain attentive to
faces and scenes (they differ slightly in each individual), Gazzaley
presented his subjects with the three tests and recorded brain
images in each case.
When asked
to remember faces, young adults showed enhanced activity in the
brain area dealing with faces and decreased activity in the area
dealing with scenes (the parahippocampal/lingual gyrus). Similarly,
when asked to remember scenes, they showed enhanced activity in the
scene area of the brain and suppressed activity in the area dealing
with faces.
Older
adults, however, while showing comparable enhancement of the face
area when asked to concentrate on faces, exhibited poor or no
suppression of the scene area, and vice versa.
"These data
suggest that older individuals are able to focus on pertinent
information, but are overwhelmed by interference from failing to
ignore distracting information, resulting in memory impairment," the
authors wrote.
D'Esposito
said that the technique Gazzaley developed to probe focusing and
ignoring ability opens the door to numerous experiments that could
shed light on a popular theory today - that problems of aging have
to do with a decline in the brain's frontal lobe.
"The
frontal lobes are the highest level of cognition and the area that
integrates information from all over the brain," he said. "If you
look at the frontal lobes over time, that is the area where there is
more decline than any other part of the brain."
To shed
light on this hypothesis, Gazzaley and D'Esposito plan to look at
patients with known or presumed frontal lobe damage, to see if they
also have problems with focusing or ignoring. Also, they plan to
look at people with attention deficit disorder, addiction problems,
and mild cognitive impairment in search of evidence that these
problems too are due to dysfunction of the frontal lobe.
"There may
be unknown lesions in the frontal lobe that affect attention,"
Gazzaley said. "Aging is not a disease, but I think there likely is
a problem with top-down control that could be fixed with drugs."
"If
aging is a frontal lobe dysfunction, it is a mild form of it,"
D'Esposito said. "And if we learn something about it, then we may be
able to help and know more about patient populations that have a
more severe form of frontal lobe damage, like traumatic brain injury
and strokes and dementia."
