Prospective memory in normal aging and Alzheimer's disease

Remembering to implement intented activities such as remembering to take medications is referred to as prospective memory (PM). Studies on aging and PM show important variations in the magnitude of the effect of age. One explanation, derived from the multiprocess framework, proposes that age differences depend on retrieval processing. It is thought to be automatic for event-based PM tasks by contrast to self-initiated processing for time-based PM tasks. Older adults generally perform worse than younger ones in laboratory tasks. PM tasks show pronounced age-related deficits, particularly in tasks demanding high level of controlled strategies (e. g. in time-based tasks versus in event-based tasks or, in low salience cue condition versus high salience cue condition in event-based tasks). However, age differences in PM tasks settings differ substantially across studies: some of them show that older adults perform as well as younger ones in event-based PM tasks, especially in ecological ones. Developmental psychologists have investigated this topic, and suggested that several factors could potentially be responsible for the age-related differences observed in MP. These differences could be related to the characteristics of PM cues (e. g. the strength of the association between PM cues and intended actions), the complexity or demands of the ongoing task, or the involvement of planning processes, in other words, the involvement of executive functions. PM deficits are important in mild Alzheimer's disease, even more important than episodic memory or executive functions deficits. This article presents a critical review of cognitive and neuropsychological studies that examined whether these factors or other partly mediate the older adults deficits in prospective memory, which are more important than those observed in episodic memory. The variability of results between studies points to the concept complexity.