Sleep Reduces the Semantic Coherence of Memory Recall: An Application of Latent Semantic Analysis to Investigate Memory Reconstruction
Sleep is thought to help consolidate hippocampus-dependent memories by reactivating previously encoded neural representations, promoting both quantitative and qualitative changes in memory representations. However, the qualitative nature of changes to memory representations induced by sleep remains largely uncharacterized. In this study, we investigated how memories are reconstructed by hypothesizing that semantic coherence, defined as conceptual relatedness between statements of free recall texts and quantified using latent semantic analysis (LSA), is affected by post-encoding sleep. Short naturalistic videos of events featuring six animals were presented to 115 participants that were randomly assigned to either 12- or 24-hour delay groups featuring sleep or wakefulness. The semantic coherence of participants’ free recall responses was analyzed to test for an effect of sleep on semantic coherence between adjacent free recalled statements, and overall. The presence of sleep reduced both forms of coherence, compared to wakefulness, supporting the notion that sleep-dependent consolidation qualitatively changes the features of reconstructed memory representations by reducing semantic coherence.