Coordinated Neural Dynamics of Sleep-Dependent Memory Stabilization: Integrating Replay, Oscillatory Coupling, and Synaptic Regulation

Abstract

Memory consolidation during sleep depends on complex interactions of neural oscillations, brain networks, and molecular machinery. Here, a structured narrative review of the neural mechanisms of sleep-dependent memory consolidation is presented and analyzed, concentrating on neural replay, hippocampal sharp-wave ripples (SWRs) and thalamocortical sleep spindles and cortical slow oscillations (SOs), and on hippocampo-neocortical communication, Synaptic Homeostasis, and neurochemical regulation. Research articles from January 2003 to September 2026 were retrieved through Pub Med/MEDLINE, Scopus, Web of Science, ScienceDirect, and IEEE Xplore and analyzed. Evidence from experimental studies involving humans and animals, including relevant methods, was thematically synthesized and comparatively evaluated with respect to mechanisms, study protocols, and the validity and limitations of the existing evidence and investigations. The literature consistently reveals that sleep-dependent replay and distribution of hippocampal-dependent memories during NREM sleep are critically coupled to interactions between hippocampal SWRs and sleep spindles and SOs, fitting the primary propositions of Active Systems Consolidation (ASC) theory. Specifically, neural replay and temporal coupling of oscillations may enhance hippocampo-neocortical communication, contributing to the persistence of encoded traces. Meanwhile, the hypothesis on Synaptic Homeostasis posits, with a functional approach for long-lasting potentiation, that synaptic upscaling, under sleep, might preserve only the salient memory engrams. Moreover, REM sleep could contribute significantly to consolidation of emotional memory as well as integration of the newly stored memory, in a manner not clearly determined for others. All these aspects are modulated through several neurochemical systems, mainly consisting of acetylcholine, glutamate, GABA, dopamine, and cortisol. Methodological advances such as intracranial EEG recording, neuroimaging techniques, targeted reactivation of memories, and non-invasive brain stimulation may confirm the hypotheses about the neural mechanisms. However, methodological questions remain, including differences between human and animal studies, a broad range of methodologies, many correlative studies in humans, and inconclusive evidence of causality, regarding neuronal replay and the coordination of oscillations with synaptic homeostasis and memory maintenance. Overall, the studies confirm that sleep is a very active state in which coordination across neural elements is maintained and that this process enhances not only memory maintenance but selectively modifies previously stored representations, integrating new information with existing information at the systemic level.