Alzheimer’s disease and memory strength : gradual decline of memory traces as a function of their strength
Article [Accepted Manuscript]
Is part of
Journal of clinical and experimental neuropsychology ; vol. 38, no. 6, pp. 648-660.Author(s)
Abstract(s)
Objective
: Episodic memory impairment is at the core of amnestic mild cognitive impair-
ment (aMCI) and Alzheimer
’
s disease (AD). The origin of memory deficits may result either
from an encoding deficit or from an accelerated decline of the memory trace. The present
study explores these two hypotheses.
Method
: We used the delayed-matching-to sample
48 items (DMS-48) memory test in a group of controls, aMCI patients, and AD patients (
n
=
16 in each group). The DMS-48 offers an incidental learning phase followed by three
forced-choice recognition tests at three-minute, one-hour, and one-week delays.
Moreover, the forced-choice test distinguishes three kinds of couple items: abstract
(meaningless), paired (two similar exemplars), and unique (two different objects) items.
Results
: As predicted by the accelerated forgetting hypothesis, patients showed a
decrease in recognition performance over time. Controls also exhibited a similar decline
in performance. As predicted by the encoding deficit hypothesis, abstract items were the
most poorly recognized in AD, at both the three-minute and the one-week delays. In AD,
recognition of the paired items also dropped after the one-hour delay, followed by
unique items after a one-week delay. Patients with aMCI exhibited a performance that
was similar to controls, except for abstract items, which dropped at the one-week delay.
Conclusions
: These results are discussed in light of a third hypothesis, the memory
strength hypothesis, in order to better account for the progressive decline in memory
performance as a function of the item type in AD.
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