Institute of Cognitive Neuroscience, University College London, London WC1N 3AZ, United Kingdom.
Division of Psychiatry, University College London, London W1T 7BN, United Kingdom.
Learn Mem. 2020 Jul 15;27(8):301-309. doi: 10.1101/lm.051821.120. Print 2020 Aug.
An essential feature of episodic memory is the ability to recall the multiple elements relating to one event from the multitude of elements relating to other, potentially similar events. Hippocampal pattern separation is thought to play a fundamental role in this process, by orthogonalizing the representations of overlapping events during encoding, to reduce interference between them during the process of pattern completion by which one or other is recalled. We introduce a new paradigm to test the hypothesis that similar memories, but not unrelated memories, are actively separated at encoding. Participants memorized events which were either unique or shared a common element with another event (paired "overlapping" events). We used a measure of dependency, originally devised to measure pattern completion, to quantify how much the probability of successfully retrieving associations from one event depends on successful retrieval of associations from the same event, an unrelated event or the overlapping event. In two experiments, we saw that within event retrievals were highly dependent, indicating pattern completion; retrievals from unrelated events were independent; and retrievals from overlapping events were antidependent (i.e., less than independent), indicating pattern separation. This suggests that representations of similar (overlapping) memories are actively separated, resulting in lowered dependency of retrieval performance between them, as would be predicted by the pattern separation account.
情景记忆的一个重要特征是能够从与其他潜在相似事件相关的众多元素中回忆起与一个事件相关的多个元素。海马体模式分离被认为在这个过程中起着至关重要的作用，它通过在编码过程中对重叠事件的表示进行正交化，来减少在模式完成过程中它们之间的干扰，通过这种模式完成，可以回忆起一个或另一个事件。我们引入了一种新的范式来检验这样一种假设，即在编码过程中，相似的记忆而不是不相关的记忆会被主动分离。参与者记忆的事件要么是独一无二的，要么与另一个事件共享一个共同的元素（配对的“重叠”事件）。我们使用了一种依赖度量，最初是为测量模式完成而设计的，来量化从一个事件成功检索关联的概率与从同一事件、不相关事件或重叠事件成功检索关联的概率有多大程度的依赖。在两个实验中，我们发现事件内的检索具有高度的依赖性，表明模式完成；与不相关事件的检索是独立的；而与重叠事件的检索是反依赖性的（即低于独立性），表明模式分离。这表明相似（重叠）记忆的表示被主动分离，导致它们之间的检索性能依赖性降低，这与模式分离理论的预测是一致的。
