Working Memory and the Enactment Effect in Early Alzheimer’s Disease

This study examines the enactment effect in early Alzheimer’s disease using a novel working memory task. Free recall of action-object instruction sequences was measured in individuals with Alzheimer’s disease and older adult controls . Instruction sequences were read out loud by the experimenter (verbal-only task) or read by the experimenter and performed by the participants (subject-performed task). In both groups and for all sequence lengths, recall was superior in the subject-performed condition than the verbal-only condition. Individuals with Alzheimer’s disease showed a deficit in free recall of recently learned instruction sequences relative to older adult controls, yet both groups show a significant benefit from performing actions themselves at encoding. The subject-performed task shows promise as a tool to improve working memory in early Alzheimer’s disease. 1. Introduction Deficits in working memory (WM), a limited capacity system that supports the online manipulation and temporary storage of information [1], are considered to be a hallmark of Alzheimer’s disease (AD), even in its earliest stages [2]. Deficits in span tasks [3, 4] and dual task procedures [5, 6] emerge in the early stages of AD, and have been attributed to central executive dysfunction [7]. Of particular interest is the finding that individuals at genetic risk of developing AD show poor WM performance relative to those not at genetic risk [8, 9], highlighting the potential of such tasks to detect early AD. This study considered the usefulness of the subject-performed task (SPT) manipulation [10] in improving WM in early AD and healthy older adult controls, in a task measuring the ability to verbally repeat short sequences of instructions. The subject-performed task [10] involves verbally presenting participants with words or instructions consisting of sets of simple actions (e.g., “open the book”), which they are required to enact during this encoding phase. Recall of the actions is then subsequently tested, typically via verbal recall or recognition. In general, research shows that enacted encoding facilitates later memory performance, relative to control conditions in which no enactment occurs during encoding [11]. Cohen [10] originally hypothesised that SPT effects are nonstrategic in nature, such that encoding during SPT does not rely on active verbal or organisational strategies that are necessary during basic verbal encoding. The enactment effect may also be attributable to the development of a richer set of representations supporting performance including visual,