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Alzheimer’s Disease May Begin with Lapses in
Attention
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Routine tasks that require the
shifting of attention, such as driving a car while conversing
with a passenger, may become more challenging for people in very
early stages of Alzheimer's disease, suggests a new study from
Washington University in St. Louis. |
Nov. 9, 2005 — People in early stages of
Alzheimer's disease have greater difficulty shifting attention back and
forth between competing sources of information, a finding that offers
new support for theories that contend breakdowns in attention play an
important role in the onset of the disease.
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"Our results provide evidence that breakdowns in
attention produce a clear change in the early stages of
Alzheimer's-related dementia," said study co-author David A. Balota, a
professor of psychology in Arts & Sciences at Washington University in
St. Louis.
Published in a recent issue of the journal
Neuropsychology, the study suggests that subtle breakdowns in attention
may offer a reliable clue that a patient is grappling with early
symptoms of Alzheimer's-related dementia.
The findings are important because they offer
clinicians and researchers another tool by which to better predict and
understand dementia of the Alzheimer's type early in its history.
Psychologists focus on early detection in part because current
medications are useful only when given very early in the course of the
disease.
While it's well known that memory skills
deteriorate as Alzheimer's progresses, recent research by Balota and
Duchek, among others, have championed the notion that breakdowns in
attention may be at the heart of many cognitive problems linked to
Alzheimer's. Although memory problems also show up in early stages of
the disease, this study suggests that underlying declines in attention
may be contributing to these memory mishaps and to other cognitive
difficulties often associated with the disease.
"Because attention is prerequisite for memory, one
might suspect that attention is one of the contributing culprits, at
least early on in the disease," suggests study lead author Janet M.
Duchek, an associate professor of psychology.
Participants for the study were drawn from
volunteers at the Alzheimer's Disease Research Center at Washington
University. Duchek and Balota studied 94 older participants, average age
mid-70s, who were healthy control individuals or individuals diagnosed
with very mild, or mild dementia of the Alzheimer's type.
In an effort to gauge each group's ability to
effectively monitor and switch among competing channels of information,
Duchek and Balota relied on a well-established psychological testing
technique know as the dichotic listening task.
The Dichotomy
Developed in the 1950s, the dichotic listening test
plays off the fact that humans are hardwired to process sensory
information in a cross-lateral fashion - words heard in the left ear
tend to be processed in the right hemisphere of the brain, and
vice-versa. Since the left hemisphere of the brain is typically dominant
for language processing, words presented in the right ear often have an
advantage over words presented simultaneously in the left ear — the
right ear-left hemisphere processing channel is said to be "pre-potent"
in that it has a default processing advantage over the left ear-right
hemisphere channel.
Using the dichotic listening task, Duchek and
Balota presented participants with distinct streams of audio information
via headphones. One stream of information — computer-generated speech
naming three digits (such as 4, 3, 1) — went to the left ear; a
different stream (such as 9, 2, 5) went to the right ear.
By asking participants to recall numbers in the
order they were presented to either ear, the researchers were able to
measure an individual's ability to switch back and forth between
right-left processing channels, and more importantly, to monitor how
well attention skills allowed them to overcome the "pre-potent" tendency
to favor information presented to the default right ear-left hemisphere
language channel.
As predicted, people with early dementia tended to
rely more often on the default channel, reporting digits presented to
the right ear far better than they reported digits presented to the left
ear. When the researchers controlled for overall recall performance, the
mild dementia group recalled 21.7% more information from their right ear
vs. left ear, and even the very mildly affected group recalled 11.3%
more from the right ear. The control participants only recalled 5.8%
more from the right vs. left ear.
The right-ear advantage increased with dementia
severity. People farther along in the disease relied even more on the
dominant left-side channel; in other words, they found it even harder to
override the usual path to process what went through the left ear to the
right brain. Poor attentional control can leave people falling back on
familiar, pre-programmed information pathways.
The study confirms that very early in the disease,
people have problems with selective attention. This problem, although
not as obvious as memory loss, may also explain why early-stage patients
start to struggle with everyday tasks that call for processing a lot of
information, such as driving. This speculation is supported by prior
findings that performance on dichotic listening predicts accident rates
in commercial bus drivers.
Findings from this study, the research team
suggests, converge with accumulating evidence that individuals with
early stage Alzheimer's Disease have breakdowns controlling prepotent
pathways across a variety of experimental paradigms, which place minimal
demands on memory systems.
"Our hope," Duchek said, "is that this work
increases recognition that Alzheimer's Disease is not simply a disease
of memory."
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