Examining sleep's role in memory generalization and specificity through the lens of targeted memory reactivation

Two vital memory functions — remembering specific experiences and generalizing across many experiences — are in tension with each other. In the complementary-learning-systems model, the hippocampus allows for fast learning of unique episodic memories while the cortex slowly extracts regularities from overlapping representations. Whereas episodic memories undergo consolidation over protracted time periods, many questions remain about how memory generalization evolves over time. Sleep's role in consolidating individual memories has been convincingly demonstrated using targeted memory reactivation, a method whereby memories can be selectively strengthened through the unobtrusive presentation of learning-related stimuli during sleep. In this review, we argue that targeted memory reactivation can help advance understanding of memory transformation and the contrast between specificity and generalization.