Chapter 32 - Sleep and Memory Consolidation: Conceptual and Methodological Challenges

Abstract

Abstract There is broad consensus that sleep benefits the consolidation, reorganization, and retrieval of learned information. Mechanisms thought to mediate memory consolidation during sleep include the hormonal milieu (low cortisol levels), specific patterns of oscillatory brain activity (sharp-wave ripples (SWR), delta activity, and slow oscillations), and neuronal replay or reactivation of encoding-related network activity. We review evidence that these presumed “sleep-dependent” consolidation mechanisms also operate during wakefulness. Importantly, studies that successfully dissociate sleep from these mechanisms (e.g., SWRs, neuronal replay/reactivation, or slow oscillations without sleep) indicate that they mediate consolidation even when they occur without behavioral and polysomnographic sleep, particularly during quiet wakefulness. However, the common use of an “active wake” condition serves to actively inhibit the operation of consolidation mechanisms, thus amplifying the apparent difference in memory between sleep and waking. The evidence that cellular consolidation mechanisms are functional during both sleep and wakefulness challenges the notion of a specialized or critical role of sleep per se in memory consolidation. A stringent test of the role of sleep in memory storage necessitates the inclusion of control conditions that allow for the maximal engagement of consolidation mechanisms in the absence of behavioral and polysomnographic sleep.