Rehearsal, schematic congruency and sleep-associated consolidation

Background Memories fade over time, but reengaging with learned materials can help to reduce memory decay. Memory rehearsal can be carried out via relearning or retrieval practice. Typically, relearning benefits retention in the short-term (Bai, Bridger, Zimmer, & Mecklinger, 2015; Kornell, Bjork, & Garcia, 2011; Roediger & Karpicke, 2006), whereas longer-term advantages have been observed following retrieval practice (Carpenter, Pashler, Wixted, & Vul, 2008; Roediger & Karpicke, 2006). Interestingly, overnight sleep, as compared to daytime wakefulness, facilitates the consolidation of relearned but not retested memories (Bäuml, Holterman & Abel, 2014; Antony & Paller, 2018). It has been suggested that retrieval practice prompts a rapid consolidation of new information, potentially via similar mechanisms to those underpinning the benefits of sleep for memory (Antony, Ferreira, Norman, & Wimber, 2017). We will test this hypothesis using a source memory paradigm, assessing the effects of relearning and retrieval practice on sleep- and wake-based consolidation. Previous work has suggested that memories compatible with pre-existing cognitive schemata benefit from sleep to a greater extent than those that are schematically-incongruent (Durrant, Cairney, McDermott, & Lewis, 2015; Lewis & Durrant, 2011). Moreover, synaptic downscaling during sleep might diminish weak and incongruent representations below a threshold for successful retrieval (Tononi & Cirelli, 2003, 2006). Whether the overlap between new information and existing knowledge influences interactions between online rehearsal and sleep-associated memory processing, however, is unknown. We will examine this question by gauging the plausibility of newly formed source memories, enabling us to determine the fate of schematically-congruent and incongruent representations. Procedure Learning will take place in the morning (wake group) or evening (sleep group). On each learning trial, participants will be presented with a noun (e.g. ‘elephant’) and a colour (e.g. red). Participants will be asked to imagine the referent of the noun in the given colour and indicate whether it is a plausible or implausible combination (e.g. a red elephant is implausible). Baseline memory performance will be assessed immediately after learning. The nouns presented at learning will be intermixed with foils. On each test trial, participants will be presented with a noun and asked to indicate if it is ‘Old’ or ‘New’. For ‘Old’ responses, participants will also be asked to identify the colour associated with the noun (red, yellow, green or blue). Where the colour is correctly identified, the noun-colour pairings will be randomly and equally divided into three conditions (Relearning, Retrieval Practice and No Rehearsal). After a short break, participants will complete another round of learning for noun-colour pairings in the Relearning condition and another round of testing for noun-colour pairings in the Retrieval Practice condition. Noun-colour pairings in the No Rehearsal condition will not undergo any rehearsal. Participants will return for follow-up sessions at 12 hours and 24 hours after learning. In each follow-up session, they will repeat the baseline memory test.