sleep enforces the temporal order in memory睡在内存中执行时间顺序.pdf

Sleep Enforces the Temporal Order in Memory Spyridon Drosopoulos, Eike Windau, Ullrich Wagner, Jan Born* ¨ ¨ Department of Neuroendocrinology, University of Lubeck, Lubeck, Germany Background. Temporal sequence represents the main principle underlying episodic memory. The storage of temporal sequence information is thought to involve hippocampus-dependent memory systems, preserving temporal structure possibly via chaining of sequence elements in heteroassociative networks. Converging evidence indicates that sleep enhances the consolidation of recently acquired representations in the hippocampus-dependent declarative memory system. Yet, it is unknown if this consolidation process comprises strengthening of the temporal sequence structure of the representation as well, or is restricted to sequence elements independent of their temporal order. To address this issue we tested the influence of sleep on the strength of forward and backward associations in word-triplets. Methodology/Principal Findings. Subjects learned a list of 32 triplets of unrelated words, presented successively (A-B-C) in the center of a screen, and either slept normally or stayed awake in the subsequent night. After two days, retrieval was assessed for the triplets sequentially either in a forward direction (cueing with A and B and asking for B and C, respectively) or in a backward direction (cueing with C and B and asking for B and A, respectively). Memory was better for forward than backward associations (p,0.01). Sleep did not affect backward associations, but enhanced forward associations, specifically for the first (AB) transitions (p,0.01), which were generally more difficult to retrieve than the second transitions. Conclusions/Significance. Our data demonstrate