Prospective memory (PM) is the ability to remember to produce an action at a specific moment in the future signaled by the occurrence of a specific event (EB condition), a time or a time interval (TB condition). Detection of the appropriate moment corresponds to the prospective component (PC), while production of the appropriate action corresponds to the retrospective (RC) component. Although PM difficulties have been reported in healthy aging and in association with Multiple Sclerosis (MS), PM has not been examined in elderly people with MS (PwMS), which is particularly relevant since their life expectancy has improved significantly in recent years due to available treatments, and PM is essential to daily functioning. The main objective of this study was to investigate whether the decline in PM performance with advancing age is influenced by the presence of multiple sclerosis (MS). This study also aimed to clarify the type of PM impairment (PC vs RC in TB and EB conditions) in MS as a function of age.

A total of 80 participants were recruited and separated into four groups: elderly PwMS (n = 20), young PwMS (n = 20), elderly healthy controls (HC) (n = 20) and young HC (n = 20). PM and its components were measured using the TEMP, an experimental ecological tool developed by our laboratory that has been validated in previous studies. In addition, all participants underwent a series of neuropsychological tests specific to MS (MACIFMS) and aging (Boston Naming Test, Clock Drawing Test, Towers of London, Trail making Test, Stroop, MoCA).

On the TEMP total score, a two-way ANOVA showed a main effect of age (F[1,75]=47.4, p<0.001, n2 = .40), a main effect of the presence of MS (F[1,75]=19.51, p<0.001, n2 = .21) as well as a significant Age X Disease interaction (F[2,74] =5.40, p=0.023, n2 = .07). Direct comparison between EB and TB conditions revealed that for the PC, only elderly PwMS had more difficulty in the TB than in the EB condition (Z = -2.51, p = 0.012), whereas RC score was significantly lower in the TB than in the EB condition in all groups except in younger controls (younger PwMS : Z = -2.56, p = 0.01; elderly HC : Z = -3.31, p < 0.001; elderly PwMS :Z = -3.04, p = 0.002).

The TEMP revealed a marked impairment in PM in elderly PwMS compared to elderly HC and young PwMS. This impairment was particularly evident on the PC component in the TB condition. RC difficulties noted in the TB condition in all but younger controls reflect the arbitrary nature of the cue-action link that is particularly sensitive to episodic memory difficulties often observed in aging and MS.