Spindle-dependent memory consolidation in healthy adults: A meta-analysis

Accumulating evidence suggests a central role for sleep spindles in the consolidation of new memories. However, no metaanalysis of the association between sleep spindles and memory performance has been conducted so far. Here, we report meta-analytical evidence for spindle-memory associations and investigate how multiple factors, including memory type, spindle type, spindle characteristics, and EEG topography affect this relationship. The literature search yielded 53 studies reporting 1424 effect sizes, resulting in a small to moderate effect for the average association. We further found that spindle-memory relationships were significantly stronger for procedural memory than for declarative memory. Neither spindle types nor EEG scalp topography had an impact on the strength of the spindlememory relation, but we observed a distinct functional role of global and fast sleep spindles, especially for procedural memory. We also found a moderation effect of spindle characteristics, with spindle frequency and power showing the largest effect sizes. Collectively, our findings suggest that sleep spindles are involved in learning and plasticity, thereby representing a general physiological mechanism for memory consolidation. Highlights Spindle measures showed a small to medium-sized association with memory performance. This relationship was stronger for procedural memory than declarative memory. No moderation effects of spindle type and EEG scalp topography have been observed. Spindle frequency and power emerged as the strongest predictors. Naps showed similar spindle-related consolidation mechanisms to whole-night sleep.