Forgetting Rates of Prose Memory in Mild Cognitive Impairment

Background: Some authors report steeper slopes of forgetting in early Alzheimer's disease (AD), while others do not. Contrasting findings are thought to be due to methodological inconsistencies or variety of testing methods, yet they also emerge when people are assessed on the same testing procedure. Objective: We aimed to assess if forgetting slopes of people with mild cognitive impairment due to AD (MCI-AD) are different from age-matched healthy controls (HC) by using a prose paradigm. Methods: Twenty-nine people with MCI-AD and twenty-six HC listened to a short prose passage and were asked to freely recall it after delays of 1 h and 24 h. Results: Generalized linear mixed modelling revealed that, compared to HC, people with MCI-AD showed poorer encoding at immediate recall and steeper forgetting up to 1 h in prose memory as assessed by free recall and with repeated testing of the same material. Forgetting rates between groups did not differ from 1 h to 24 h. Conclusion: The differences observed in MCI-AD could be due to a post-encoding deficit. These findings could be accounted either by a differential benefit from retrieval practice, whereby people with MCI-AD benefit less than HC, or by a working memory deficit in people with MCI-AD, which fails to support their memory performance from immediate recall to 1 h.