Odor cueing during sleep improves consolidation of a history lesson in a school setting

Abstract

Sleep is a key factor in memory consolidation. During sleep, information is reactivated, transferred, and redistributed to neocortical areas, thus favoring memory consolidation and integration. Although these reactivations occur spontaneously, they can also be induced using external cues, such as sound or odor cues, linked to the acquired information. Hence, targeted memory reactivation during sleep represents an advantageous tool for improving memory consolidation in real-life settings. In this study, our goal was to improve the consolidation of complex information such as that of a history lesson, using a school study session in the presence of an odor, and a reactivation round while sleeping at home on the same night of the acquisition, without using additional study sessions. We found that complex information can be associated with an odor in the classroom and that one session of reactivation during the first night of sleep in the students' houses improves its consolidation. These results bring new evidence for the implementation of reactivation during sleep in real-life settings.

Figure 1

(a) The history lesson was presented by their teacher, using a PowerPoint presentation on a projector screen. Each slide was shown for 1.5 min as she commented on them orally (day 1). Short-term testing: Students made an evaluation consisting of 13 multiple-choice questions with four possible answers and one correct answer; they had no time limit to answer them and all the right answers had been previously presented on the slides during the training. Night 1: Reactivation: At home, half of the volunteers used dispensers containing the congruent odor A (coconut), whereas the other half used dispensers containing the incongruent odor B (violets) (depending on which group they were assigned to) at the time they went to sleep for 1.5 h. The odor was sprayed every 15 min. Day 8: Long-term testing: Students made another evaluation consisting of 13 multiple-choice questions with four possible answers and one correct answer; they had no time limit to answer them and all the right answers had been previously presented on the slides during the training on day 1. (b) Mean percentage of correct answers at testing sessions on days 1 and 8 ± SEM for the TMR and No-TMR groups. (c) Mean memory change ± SEM for the TMR and No-TMR groups. *, p < 0.05; ***, p < 0.001. Icons made by Freepik.