Sleep supports memory consolidation, and slow-wave sleep (SWS) in particular is assumed to benefit the consolidation of verbal learning material. Re-exposure to previously learned words during SWS with a technique known as targeted memory reactivation (TMR) consistently benefits memory. However, TMR has also been successfully applied during sleep stage N2, though a direct comparison between words selectively reactivated during SWS versus N2 is still missing. Here, we directly compared the effects of N2 TMR and SWS TMR on memory performance in a vocabulary learning task in a within-subject design. Thirty-four healthy young participants (21 in the main sample and 13 in an additional sample) learned 120 Dutch–German word pairs before sleep. Participants in the main sample slept for ∼8 h during the night, while participants in the additional sample slept ∼3 h. We reactivated the Dutch words selectively during N2 and SWS in one single night. Forty words were not cued. Participants in the main sample recalled the German translations of the Dutch words after sleep in the morning, while those in the additional sample did so at 2:00 a.m. As expected, we observed no differences in recall performance between words reactivated during N2 and SWS. However, we failed to find an overall memory benefit of reactivated over nonreactivated words. Detailed time–frequency analyses showed that words played during N2 elicited stronger characteristic oscillatory responses in several frequency bands, including spindle and theta frequencies, compared with SWS. These oscillatory responses did not vary with the memory strengths of individual words. Our results question the robustness and replicability of the TMR benefit on memory using our Dutch vocabulary learning task. We discuss potential boundary conditions for vocabulary reactivation paradigms and, most importantly, see the need for further replication studies, ideally including multiple laboratories and larger sample sizes.

中文翻译：

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慢波睡眠期间的有针对性的记忆重新激活与睡眠阶段 N2：词汇任务没有显着差异

睡眠有助于记忆巩固，尤其是慢波睡眠（SWS）被认为有利于语言学习材料的巩固。在 SWS 期间，使用一种称为目标记忆重新激活 (TMR) 的技术重新接触以前学过的单词，始终有利于记忆。然而，TMR 也已成功应用于睡眠阶段 N2，尽管仍然缺少 SWS 期间选择性重新激活的单词与 N2 期间选择性重新激活的单词之间的直接比较。在这里，我们直接比较了 N2 TMR 和 SWS TMR 在受试者内设计的词汇学习任务中对记忆表现的影响。34 名健康的年轻参与者（主样本中 21 名，附加样本中 13 名）在睡觉前学习了 120 个荷兰语-德语单词对。主要样本中的参与者晚上睡了约 8 小时，而附加样本中的参与者睡了约 3 小时。我们在 N2 和 SWS 期间用一个晚上选择性地重新激活了荷兰语单词。四十个字没有提示。主样本中的参与者在早上睡觉后回忆起荷兰语单词的德文翻译，而附加样本中的参与者则在凌晨 2:00 时回忆起荷兰语单词的德语翻译。 正如预期的那样，我们观察到 N2 和 SWS 期间重新激活的单词在回忆性能上没有差异。然而，我们未能发现重新激活的单词相对于非重新激活的单词的整体记忆优势。详细的时频分析表明，与 SWS 相比，N2 期间播放的单词在多个频段（包括主轴频率和 θ 频率）引发了更强的特征振荡响应。这些振荡反应并不随着单个单词的记忆强度而变化。我们的结果质疑 TMR 使用荷兰语词汇学习任务对记忆的益处的稳健性和可复制性。我们讨论了词汇重新激活范式的潜在边界条件，最重要的是，我们看到了进一步复制研究的必要性，最好包括多个实验室和更大的样本量。