Title: Does sleep flush out the unwanted leftovers of recent cognitive activities?
Funder: Economic and Social Research Council

Abstract: This project examines whether sleep helps flush out unwanted leftovers of recent perceptual and cognitive activities in addition to consolidating new learning. Traditional views of learning assume that new memories are shaky for a while, but soon consolidate, becoming resistant to amnestic agents and interference from new learning (McGaugh, 2000; Wixted, 2004). Recent theorizing (Stickgold & Walker, 2013), however, insists that memory consolidation is not the uniform and indiscriminate process just described, but is instead highly selective and adaptive, tailored to the goal-directed needs of the organism. Sleep, with its associated neurophysiological states, is the prime vehicle for a "memory triage" process: only memories that are emotionally salient, or worth remembering for future use, get assimilated into the brain's landscape of ever evolving knowledge. Here we ask what happens to unwanted memories, which also start off in this no man's land of in between memory (i.e., between working memory and long-term memory; henceforth, IBM)? The goal of this project is to determine whether in addition to stabilizing and assimilating useful memories, sleep also cleans the slate of unwanted memories to reset the system, in order to start afresh the next day. Evidence for offline, sleep-dependent memory consolidation is substantial, showing a variety of transformative results, including increased resilience to amnestic agents, enhanced accessibility, spontaneous recovery, extraction of underlying structures, and integration with existing knowledge. In contrast, the existence of memory clean-up has not yet been substantiated. We suggest this is largely because researchers thought they could just force learners to forget newly learnt information. Our premise is that unwanted leftovers mostly comprise the lingering activation of long-term memories recently evoked by perceptual, expressive, or imagery-based experience. This activation accumulates records of involvement of a given memory over the course of a day. As such, this could influence rather insidiously how we behave during the next few hours, and perhaps for as long as we remain awake. These persisting activation byproducts are precisely what an active forgetting mechanism would get rid of. To test this hypothesis, we explore the evolution of memory traces left by language exposure and/or practice and use. Language provides an ideal testbed, as the same linguistic event can provoke both lingering effects that one would not necessarily want to keep and sleep-dependent offline consolidation of unitized new information. We already have linguistic performance measures that index both kinds of effects, and the consolidation of new lexical knowledge through sleep is well documented at this stage. Work Package 1 examines the fate of memories for novel word forms and their potential for either consolidation or clean-up. Work Package 2 provides multiple tests of whether sleep does clean the slate by removing lingering traces. Our pilot data (Fig. TA6) suggest that it does. Finally, Work Package 3 focuses on at-risk populations, namely older adults and sleep apnoea patients, to evaluate the impact of poor sleep on both memory consolidation and clean-up simultaneously. If older adults show impaired clean-up on top of consolidation problems, reduced clean-up could be one of the factors behind the gradual cognitive decline that characterizes normal aging. Our experiments focus on language memories to explore whether sleep resets what we have called IBM. Positive findings will provide a proof of concept, with a strong potential for applications in domains as varied as education, work patterns, sports science, aging, extended military missions, and neurocognitive rehabilitation.


Research activity codes: 1.2 PSYCHOLOGICAL AND SOCIOECONOMIC PROCESSES
Health categories: MENTAL HEALTH