title: Alzheimer's disease and memory strength: Gradual decline of memory traces as a function of their strength.
abstract: OBJECTIVE
  Episodic memory impairment is at the core of amnestic mild cognitive impairment (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.
  
  
  METHODS
  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.
authors.affiliation: a Centre de recherche de l'IUGM, Université de Montréal , Montréal , QC , Canada.|b Département de psychologie , Université de Montréal , QC , Canada.
authors.forename: Guillaume T
authors.initials: GT
authors.lastname: Vallet
authors.affiliation: c Département de psychologie , Université du Québec à Montréal , Montréal , QC , Canada.|d Centre de recherche, Centre hospitalier de l'Université de Montréal , Montréal , QC , Canada.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rouleau
authors.affiliation: c Département de psychologie , Université du Québec à Montréal , Montréal , QC , Canada.
authors.forename: Sophie
authors.initials: S
authors.lastname: Benoit
authors.affiliation: c Département de psychologie , Université du Québec à Montréal , Montréal , QC , Canada.
authors.forename: Roxane
authors.initials: R
authors.lastname: Langlois
authors.affiliation: e Université de Toulouse, UPS, Centre de Recherche Cerveau et Cognition, CNRS, CerCo , Toulouse , France.
authors.forename: Emmanuel J
authors.initials: EJ
authors.lastname: Barbeau
authors.affiliation: a Centre de recherche de l'IUGM, Université de Montréal , Montréal , QC , Canada.|b Département de psychologie , Université de Montréal , QC , Canada.
authors.forename: Sven
authors.initials: S
authors.lastname: Joubert
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000150:complications / Q000503:physiopathology*; D060825:Cognitive Dysfunction / Q000150:complications / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000209:etiology / Q000503:physiopathology*; D061212:Memory, Episodic; D021641:Recognition, Psychology / Q000502:physiology*; D013997:Time Factors
keywords: Alzheimer’s disease; Amnestic mild cognitive impairment; Encoding deficit; Episodic memory; Memory strength; Rapid forgetting