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Psychologists Find More Sensitive Tests for
Predicting Alzheimer's
Two news studies explore traits of those who develop
the disease
Sept. 26, 2005 - Two recent studies may help
clinicians and researchers better predict and understand the Alzheimer’s
type of dementia early in its history. These psychologists focused on
early detection, in part, because current medications are useful only
when given very early in the course of the disease.
Tests in the first study predicted future
Alzheimer’s diagnosis as much as two years early.
The study analyzed the data on 119 participants in
the Longitudinal Aging Study Amsterdam, a large, population-based study
of older people. The researchers visited older people in their homes and
gave them memory tests loaded on laptop computers. Two years later, they
compared the test scores of people who went on to develop Alzheimer’s
with the scores of those who stayed healthy.
The researchers analyzed memory components that
included episodic (what happened; what did you hear or read); semantic
(vocabulary, facts); and implicit (learning without awareness of
learning, “priming”).
Three tests were very good at predicting who would
develop Alzheimer’s by two years later. Participants for whom “priming”
information didn’t aid memory or whose learning wasn’t aided by semantic
knowledge -- were significantly more likely to develop Alzheimer’s.
The strongly predictive tests were, in order of
their power, a Paired-Associate Learning Test, which cued participants
to recall five semantically related and five semantically unrelated
pairs of words; and a Perceptual Identification Task, which measured how
fast participants read aloud words briefly presented on a computer
screen.
To test implicit memory, experimenters repeated some words to see
whether “priming” took place, which would help participants read those
words faster. The researchers also gave a Visual Association Test, which
cued participants to recall six line drawings of common objects that had
been presented earlier in an illogical interaction with another object
or cue.
On the word-pair memory test, people destined to
develop Alzheimer’s disease didn’t do any better when words were related
than when they weren’t. The authors think these participants may already
have lost key knowledge of word attributes that normally help people to
more easily remember words by means of their semantic associations.
Sometimes, at-risk participants reported a vague sense that one word had
something to do with another, but they couldn’t say exactly what. The
authors suspect they couldn’t encode the word pairs at a sufficiently
deep level because they’d lost the semantic knowledge that stays intact
in normally aging people.
On the word-reading test, word repetition (to
measure priming) didn’t help high-risk participants to perform better, a
sign that they weren’t learning implicitly as well as the people who
would stay healthy. The authors speculate that because high-risk
participants drew less benefit from word repetition, they did not encode
the words properly.
These tests remained sensitive to the risk of
developing Alzheimer’s disease even within a more homogeneous subset of
the broader study population, people with mild cognitive impairment. For
both the whole and subset study groups, these tests predicted future
Alzheimer’s diagnosis as much as two years early.
Equally important, the popular Mini Mental Status
Exam (MMSE), a test mainly sensitive to episodic memory, was not as good
a predictor. Although clinicians use it for quick, easy-to-administer
screening, the authors found it to be "less predictive [than the tests
sensitive to semantic and implicit memory]. These [MMSE and other purely
episodic memory] tasks may only differentiate between pathological and
normal aging when dementia has progressed to a more advanced stage."
This study was by psychologists Pauline Spaan, PhD,
and Jeroen Raaijmakers, PhD, from the University of Amsterdam in
collaboration with neurologist Cees Jonker, MD, PhD, from the Vrije
Universiteit in Amsterdam.
This and the following study appear in the
September issue of Neuropsychology, which is published by the American
Psychological Association (APA).
Study Two: Early in disease there are problems
of “selective attention.”
In the second Neuropsychology study, an established
psychological test has picked up early-warning signs of Alzheimer’s
disease. The report explains how the dichotic listening task, which
measures how well people process information when they hear one thing in
the left ear and another in the right ear, 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.
At the Alzheimer’s Disease Research Center at
Washington University in St. Louis, Janet Duchek, PhD and David Balota,
PhD, studied 94 participants in their early to mid-70s with healthy,
very mild, or mild dementia of the Alzheimer’s type. They looked for
information-processing breakdowns suspected to happen early in the
disease, before the appearance of language and visuospatial problems.
Problems with attention, the authors say, could “underlie the difficulty
with daily activities often seen in the early stages of the disease.”
Duchek and Balota used a dichotic listening task,
presenting information to participants 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. The psychologists measured how well participants
recalled the digits presented to each ear.
As predicted, people with early dementia
remembered the digits presented to the right ear far better than they
recalled the 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.
Clearly, people with mild or very mild Alzheimer’s
relied more heavily on the default pathway for processing information,
which for language would be the left side of the brain. In other words,
these patients had a harder time switching their attention and reporting
what they heard in the left ear, which sent information to the right
half of the brain.
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.
The study confirms that attentional processing,
like other cognitive processes, is affected early in Alzheimer’s
disease.
Poor attentional controls can leave people falling
back on familiar, “pre-programmed” information pathways. Write the
authors, “One can speculate about the importance of attentional control
in everyday tasks, such as driving.” Their speculation is supported by
prior findings that performance on dichotic listening predicts accident
rates in commercial bus drivers.
Article 1: “Early Assessment of Dementia: The
Contribution of Different Memory Components,” Pauline E.J. Spaan, PhD,
and Jeroen G.W. Raaijmakers, PhD, University of Amsterdam, and Cees
Jonker, PhD, MD, Vrije Universiteit; Neuropsychology, 2005, Vol. 19, No.
5.
Article 2: “Failure to Control Prepotent Pathways
in Early Stage Dementia of the Alzheimer’s Type: Evidence from Dichotic
Listening,” Janet M. Duchek, PhD, and David A. Balota, PhD, Washington
University; Neuropsychology, 2005, Vol. 19, No. 5.
About source:
The American Psychological Association (APA), in
Washington, DC, is the largest scientific and professional organization
representing psychology in the United States and is the world’s largest
association of psychologists. APA’s membership includes more than
150,000 researchers, educators, clinicians, consultants and students.
Through its divisions in 53 subfields of psychology and affiliations
with 60 state, territorial and Canadian provincial associations, APA
works to advance psychology as a science, as a profession and as a means
of promoting human welfare.
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