Effects of Sleep and Age on Prospective Memory Consolidation: A Walk in a Virtual Museum

Abstract

Prospective memory (PM) refers to our ability to perform actions at the appropriate moment, either when a predetermined event occurs (event-based, EB) or after a predetermined amount of time (time-based, TB). Sleep favors the consolidation of both EB and TB intentions, but whether this benefit is preserved during ageing is still subject to debate. PM was assessed in 28 young and 27 older healthy volunteers using a virtual environment. Participants had to learn and execute intentions after intervals filled with either daytime wakefulness or nighttime sleep. Intentions consisted of four TB, four EB with a strong link between the cue triggering retrieval and the action to be performed (EB-link) and four with no link (EB-nolink). PM was not affected by age, whatever the type of intention and the nature of the retention interval. While sleep reinforced all types of intentions in young participants, this benefit was only observed for TB and EB-link intentions in older adults. Sleep also reinforced the intrinsic PM components in both groups. Thus, when assessed using complex realistic situations, PM is not impaired in ageing. Results are discussed in the light of memory schema theory and the possible impact of cognitive reserve on sleep and memory.

Keywords: ageing; cognitive reserve; memory schemas; prospective memory; sleep; virtual reality.

Figure 1

Study protocol. All participants came to the laboratory for three sessions, separated by at least 7 days. The first session included a familiarization phase with the virtual environment, followed by a learning phase and short-term (10 min) recall of intentions. This session was performed either in the morning or in the evening to control for a potential circadian confound. Participants then performed two further sessions in the wake and sleep conditions (counterbalanced order). In the sleep session, participants had a regular night of sleep at home. Wrist actigraphy was used to control for the absence of naps in the wake session and compliance with the sleep-wake schedule for the sleep condition.

Figure 2

Representation of the virtual environment. This environment recreated the ground floor of the Memorial peace museum located in Caen, which is dedicated to World War II. Participants interacted with the virtual environment from a first-person perspective using a USB-wired controller with two joysticks and two buttons. The left joystick controlled the movements and the right joystick-controlled camera. The X and Y buttons enabled participants to view a clock and a map of the environment. These remained accessible throughout the exploration. The clock displayed a virtual time that served as the prospective cue for TB intentions. The map represented the virtual environment, showing with the names of relevant locations and the participant’s position.

Figure 3

Effect of 12-h retention intervals filled with either daytime wakefulness or sleep on the recall of EB-link, EB-nolink and TB intentions (expressed as mean performance ± standard error of the mean (SEM)) in young and older adults (YA and OA, respectively). **: p < 0.01; ***: p < 0.001.

Figure 4

Effect of 12-h retention intervals filled with either daytime wakefulness or sleep on the recall of the prospective, retrospective, and associative components of intentions (expressed as mean performance ± standard error of the mean (SEM)) in young and older adults (YA and OA respectively). **: p < 0.01; ***: p < 0.001.