Optimizing Methodology of Sleep and Memory Research in Humans

Abstract

Understanding the complex relationship between sleep and memory is a major challenge in neuroscience. Many studies on memory consolidation in humans suggest that sleep triggers offline memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, issues related to non-optimal experimental designs, task characteristics and measurements, and inappropriate data analysis practices can significantly affect the interpretation of the effect of sleep on memory. In this article, we discuss these issues and suggest constructive solutions to address them. We believe that implementing these solutions in future sleep and memory research will significantly advance this field by improving the understanding of the specific role of sleep in memory consolidation.

Sleep selectively and durably enhances real-world sequence memory

“…Evidence in humans is consistent with this proposed mechanismepisodic memory performance varies with SWS duration and microstructure (e.g., (17); for reviews, see (8,18)), particularly temporal or phase-based spindle-slow wave coupling, which is thought to facilitate replay-linked synaptic plasticity (15,19). However, the evidence for sleep's active role in shaping episodic memory is mixed, with failed replications and task-dependence rendering unclear which retrieval tasks or processes should be most affected (20,21). Moreover, the presumption that sleeprelated consolidation transforms memories from specific (i.e., episodic) to abstracted, generalized knowledge via hippocampal-to-cortical information transfer (8,15,22), does not explain the role of sleep (if any) in stabilizing or enhancing episodic memory for specific experiences.…”

“…Theories of sleep-related memory consolidation hinge on the notion that sleep’s effects on memory are active and selective, leading memories to be qualitatively transformed, not merely protected (8, 17, 18). However, the case for preferential consolidation of certain types of episodic memory (e.g., emotional memoranda) over others has been complicated in recent years by failed replications (6, 20), and the effect of sleep on memory consolidation is still actively debated (10, 21). Using an immersive real-world encoding event, we found in two independent samples that sleep selectively and actively enhanced memory for sequence associations – but not featural associations – despite sequence and featural memory probes being matched on difficulty overall.…”

“…However, the evidence for sleep’s active role in shaping episodic memory is mixed, with failed replications and task-dependence rendering unclear which retrieval tasks or processes should be most affected (20, 21). Moreover, the presumption that sleep-related consolidation transforms memories from specific (i.e., episodic) to abstracted,…”