Distinct and shared cognitive functions mediate event- and time-based prospective memory impairment in normal ageing

Abstract

Prospective memory (PM) is the ability to remember to perform an action at a specific point in the future. Regarded as multidimensional, PM involves several cognitive functions that are known to be impaired in normal ageing. In the present study we set out to investigate the cognitive correlates of PM impairment in normal ageing. Manipulating cognitive load, we assessed event- and time-based PM, as well as several cognitive functions, including executive functions, working memory, and retrospective episodic memory, in healthy participants covering the entire adulthood. We found that normal ageing was characterised by PM decline in all conditions and that event-based PM was more sensitive to the effects of ageing than time-based PM. Whatever the conditions, PM was linked to inhibition and processing speed. However, while event-based PM was mainly mediated by binding and retrospective memory processes, time-based PM was mainly related to inhibition. The only distinction between high- and low-load PM cognitive correlates lies in an additional, but marginal, correlation between updating and the high-load PM condition. The association of distinct cognitive functions, as well as shared mechanisms with event- and time-based PM, confirm that each type of PM relies on a different set of processes.

Figures

Figure 1

Design of the event-based (a) and time-based (b) prospective memory (PM) tasks (see Method).

Figure 2

Interaction effects between age (young, middle-aged and older groups) and nature of PM (event-based and time-based conditions) and between age and cognitive load (high and low load conditions). The Y-axis displays the mean scores obtained by each group in the EBPM and TBPM conditions (on the left) and in the low and the high load PM conditions (on the right). t: trend; *p<.05; **p<.01. Note: ANOVA on 52 subjects demonstrated the same pattern of results except that the main effect of Nature of PM became marginal, F(1, 49) = 3.83; p < 0.06. Post hoc tests revealed that, in EBPM, older group had weaker performance than younger and middle-aged groups (p < 0.001 and p < 0.05). There was no age effect on TBPM. The effect of nature was only significant for the older group (p < 0.01).

Figure 3

Interaction effect for time monitoring between Load condition (high vs. low load) and period (first minute vs., second minute vs. third/critical minute). The Y-axis displays the time-checking frequency (number of times the subjects checked the clock, averaged over the three groups).

Figure 4

Mediation analyses on the relationships between age and event-based prospective memory (a; b; c) and between age and time-based prospective memory (d). Numbers refer to betas of the regressions and numbers in italic in parentheses represent the betas of the regressions controlling for the mediator. t: trend; *p<.05; **p<.01; ***p<.001.