Working memory in mild cognitive impairment and Alzheimer's disease: Contribution of forgetting and predictive value of complex span tasks.

Abstract

This study examines working memory (WM) in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Performances on sentence span and operation span were measured in individuals meeting criteria for MCI (n = 20) and AD (n = 16) as well as in healthy older adults (n = 20). In addition, the effect of retention interval was assessed by manipulating the length of first and last items of trials (long-short vs. short-long), as forgetting might contribute to impaired performance in AD and MCI. Results show a group effect (p < .001, η² = .47): In both conditions and for both material types, WM span is lower in AD than in MCI (p < .001), which in turn is lower than in healthy aging (p < .05). An effect of retention interval on complex span was found for all groups (p < .001, η² = .57), supporting a role for forgetting within WM. When computing a proportional interval effect (p < .05, η² = .12), it was found that persons with AD were more sensitive to retention interval than were healthy older adults (p < .05). Among persons with MCI, those who later showed significant clinical deterioration or progression to AD were more affected by retention interval (p < .05, η² = .28) than were those who remained stable. Furthermore, deficits in AD are associated with a higher proportion of intrusion errors, particularly those from the current trial (p < .05, η² = .15), which could reflect inhibitory processes. Overall, these results indicate impaired WM in age-related disorders with a gradient between MCI and AD. Retention interval increases deficit in persons with AD. It also shows potential in predicting a negative prognosis in those with MCI.