Systems memory consolidation during sleep: oscillations, neuromodulators, and synaptic remodeling.

Abstract

Memory consolidation transforms newly acquired experiences into stable long-term memories essential for learning and cognition. This process involves systems consolidation, where memory traces are reorganized across brain regions, and synaptic consolidation, which fine-tunes local neural connections. Sleep plays a critical role in both, coordinating memory reactivation, synaptic remodeling, and long-range neural communication. Systems consolidation is supported by stagespecific brain oscillations: during NREM sleep, the coupling of slow-oscillations, spindles, and sharp-wave ripples facilitates hippocampal-cortical transfer of memory representations, while REM sleep theta oscillations contribute to memory integration, abstraction, and emotional tagging. Complementary neuromodulatory dynamics, particularly involving norepinephrine and dopamine, regulate the timing and prioritization of memory processing. At the synaptic level, sleep balances strengthening and weakening of connections through a coordinated interplay of NREM and REM activity. Recent findings also suggest that dreaming may reflect the subjective correlate of these processes, particularly through the integration of recent and remote memory fragments. Although the precise relationship between systems-level reorganization and local synaptic refinement remains unclear-partly due to current technical limitations-emerging approaches are beginning to bridge these scales. Together, these findings underscore the integrative role of sleep in optimizing memory consolidation and offer promising avenues for clinical and translational research.