WASHINGTON -- Two recent studies may help clinicians and researchersbetter predict and understand dementia of the Alzheimer's type early inits history. Both studies appear in the September issue ofNeuropsychology, which is published by the American PsychologicalAssociation (APA). Psychologists focus on early detection in partbecause current medications are useful only when given very early inthe course of the disease.
In the first study, psychologists Pauline Spaan, PhD, and JeroenRaaijmakers, PhD, from the University of Amsterdam in collaborationwith neurologist Cees Jonker, MD, PhD, from the Vrije Universiteit inAmsterdam analyzed the data on 119 participants in the LongitudinalAging Study Amsterdam, a large, population-based study of older people.The researchers visited older people in their homes and gave themmemory tests loaded on laptop computers. Two years later, they comparedthe test scores of people who went on to develop Alzheimer's with thescores of those who stayed healthy.
The researchers analyzed memory components that included episodic (whathappened; what did you hear or read); semantic (vocabulary, facts); andimplicit (learning without awareness of learning, "priming"). Threetests were very good at predicting who would develop Alzheimer's by twoyears later. Participants for whom "priming" information didn't aidmemory or whose learning wasn't aided by semantic knowledge -- weresignificantly more likely to develop Alzheimer's.
The strongly predictive tests were, in order of their power, aPaired-Associate Learning Test, which cued participants to recall fivesemantically related and five semantically unrelated pairs of words;and a Perceptual Identification Task, which measured how fastparticipants read aloud words briefly presented on a computer screen.To test implicit memory, experimenters repeated some words to seewhether "priming" took place, which would help participants read thosewords faster. The researchers also gave a Visual Association Test,which cued participants to recall six line drawings of common objectsthat had been presented earlier in an illogical interaction withanother object or cue.
On the word-pair memory test, people destined to develop Alzheimer'sdisease didn't do any better when words were related than when theyweren't. The authors think these participants may already have lost keyknowledge of word attributes that normally help people to more easilyremember words by means of their semantic associations. Sometimes,at-risk participants reported a vague sense that one word had somethingto do with another, but they couldn't say exactly what. The authorssuspect they couldn't encode the word pairs at a sufficiently deeplevel because they'd lost the semantic knowledge that stays intact innormally aging people.
On the word-reading test, word repetition (to measure priming) didn'thelp high-risk participants to perform better, a sign that they weren'tlearning implicitly as well as the people who would stay healthy. Theauthors speculate that because high-risk participants drew less benefitfrom word repetition, they did not encode the words properly.
These tests remained sensitive to the risk of developing Alzheimer'sdisease even within a more homogeneous subset of the broader studypopulation, people with mild cognitive impairment. For both the wholeand subset study groups, these tests predicted future Alzheimer'sdiagnosis as much as two years early.
Equally important, the popular Mini Mental Status Exam (MMSE), a testmainly sensitive to episodic memory, was not as good a predictor.Although clinicians use it for quick, easy-to-administer screening, theauthors found it to be "less predictive [than the tests sensitive tosemantic and implicit memory]. These [MMSE and other purely episodicmemory] tasks may only differentiate between pathological and normalaging when dementia has progressed to a more advanced stage."
In the second Neuropsychology study, an established psychological testhas picked up early-warning signs of Alzheimer's disease. A new studyin the September issue of Neuropsychology explains how the dichoticlistening task, which measures how well people process information whenthey hear one thing in the left ear and another in the right ear,confirms that very early in the disease, people have problems withselective attention. This problem, although not as obvious as memoryloss, may also explain why early-stage patients start to struggle witheveryday tasks that call for processing a lot of information -- such asdriving.
At the Alzheimer's Disease Research Center at Washington University inSt. Louis, Janet Duchek, PhD and David Balota, PhD, studied 94participants in their early to mid-70s with healthy, very mild, or milddementia of the Alzheimer's type. They looked forinformation-processing breakdowns suspected to happen early in thedisease, before the appearance of language and visuospatial problems.Problems with attention, the authors say, could "underlie thedifficulty with daily activities often seen in the early stages of thedisease."
Duchek and Balota used a dichotic listening task, presentinginformation 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 theright ear. The psychologists measured how well participants recalledthe digits presented to each ear.
As predicted, people with early dementia remembered the digitspresented to the right ear far better than they recalled the digitspresented to the left ear. When the researchers controlled for overallrecall performance, the mild dementia group recalled 21.7% moreinformation from their right ear vs. left ear, and even the very mildlyaffected group recalled 11.3% more from the right ear. The controlparticipants only recalled 5.8% more from the right vs. left.
Clearly, people with mild or very mild Alzheimer's relied more heavilyon the default pathway for processing information, which for languagewould be the left side of the brain. In other words, these patients hada harder time switching their attention and reporting what they heardin the left ear, which sent information to the right half of the brain.
The right-ear advantage increased with dementia severity. Peoplefarther along in the disease relied even more on the dominant left-sidechannel; in other words, they found it even harder to override theusual path to process what went through the left ear to the rightbrain.The study confirms that attentional processing, like other cognitiveprocesses, is affected early in Alzheimer's disease. Poor attentionalcontrols can leave people falling back on familiar, "pre-programmed"information pathways. Write the authors, "One can speculate about theimportance of attentional control in everyday tasks, such as driving."Their speculation is supported by prior findings that performance ondichotic listening predicts accident rates in commercial bus drivers.
Article 1: "Early Assessment of Dementia: The Contribution of DifferentMemory 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 StageDementia 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.
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