Sleep bolsters schematically incongruent memories

Abstract

Our ability to recall memories is improved when sleep follows learning, suggesting that sleep facilitates memory consolidation. A number of factors are thought to influence the impact of sleep on newly learned information, such as whether or not we rehearse that information (e.g. via restudy or retrieval practice), or the extent to which the information is consistent with our pre-existing schematic knowledge. In this pre-registered, online study, we examined the effects of both rehearsal and schematic congruency on overnight consolidation. Participants learned noun-colour pairings (e.g. elephant-red) and rated each pairing as plausible or implausible before completing a baseline memory assessment. Afterwards, participants engaged in a period of restudy or retrieval practice for the pairings, and then entered a 12 h retention interval of overnight sleep or daytime wakefulness. Follow-up assessments were completed immediately after sleep or wake, and again 24 h after learning. Our data indicated that overnight consolidation was amplified for restudied relative to retested noun-colour pairings, but only when sleep occurred soon after learning. Furthermore, whereas plausible (i.e. schematically congruent) pairings were generally better remembered than implausible (i.e. schematically incongruent) pairings, the benefits of sleep were stronger for implausible relative to plausible memories. These findings challenge the notion that schema-conformant memories are preferentially strengthened during post-learning sleep.

Fig 1. Experimental procedure and tasks.

(A) Participants completed an encoding phase, a baseline memory test and a memory rehearsal phase in the morning (wake group) or evening (sleep group). Participants returned 12 h and 24 h later to complete follow-up memory tests. (B) On each encoding trial, participants were presented with a noun and a coloured square. Participants were asked to imagine the referent of the noun in the given colour and indicate whether it was a plausible or implausible combination. (C) On each test trial, participants were asked to decide whether a noun was ‘old’ (i.e. they had seen the noun at encoding) or ‘new’ (i.e. they had not seen the noun at encoding). For ‘old’ responses, participants were asked to select the colour that had appeared with the noun at encoding. For ‘new’ responses participants were asked to indicate the location of the letter ‘X’.

Fig 2. Source memory retention and rehearsal, 12h follow-up.

Source memory retention at the 12 h follow-up for the sleep and wake groups. Data is shown for each rehearsal condition, collapsed across the plausibility conditions. Error bars represent SEM. *** p < .001.

Fig 3. Source memory retention and rehearsal, 24-hour follow-up.

Source memory retention at the 24 h follow-up for the sleep and wake groups. Data is shown for each rehearsal condition, collapsed across the plausibility conditions. Error bars represent SEM. *** p ≤ .001, NS = not significant.

Fig 4. Source memory retention and schematic congruency.

Memory retention at the (A) 12 h and (B) 24 h follow-ups for the plausible and implausible conditions. Data are collapsed across the rehearsal conditions. Error bars represent SEM. *** p ≤ .001, ** p ≤ .01.

Fig 5. Source memory retention and schematic congruency (recalculated at 24 h).

Memory retention at the 24 h follow-up with retention scores recalculated as the proportion of retention at the 12 h follow-up (scores > 100% indicate an improvement between the time points). Data are collapsed across the rehearsal conditions. Error bars represent SEM. ** p ≤ .01, NS = not significant.