Hippocampal contributions to declarative memory consolidation during sleep

The human brain faces a fundamental information storage challenge— forming useful new memories while not over-writing important old ones. Memory consolidation, and the corresponding interplay between the hippocampus and neocortex, is a protracted process to adjudicate between these two competing factors. Converging evidence from behavioral, cellular, and systems neuroscience strongly implicates a special role for sleep in stabilizing new declarative memories. In this chapter, we review evidence that during sleep the reactivation of newly acquired neuronal traces has lasting implications for memory transformation and stabilization. We first summarize relevant theoretical issues in memory research and then outline the physiological properties of sleep that may allow for this reactivation. We consider many factors that affect spontaneous memory reactivation, and we highlight research showing that memories can be selectively targeted and modified using learning-related stimuli. Ultimately, the ability to rescue otherwise fleeting episodes from oblivion plays a vital role in human life. Research elucidating this ability will also be critical for understanding how memory breaks down in aging and disease.