Ruch Simon, Fehér Kristoffer, Homan Stephanie, Morishima Yosuke, Mueller Sarah Maria, Mueller Stefanie Verena, Dierks Thomas, Grieder Matthias
Cognitive Neuroscience of Memory and Consciousness, Institute of Psychology, University of Bern, 3012 Bern, Switzerland.
Department of Neurosurgery and Neurotechnology, Institute for Neuromodulation and Neurotechnology, University of Tübingen, 72076 Tübingen, Germany.
Brain Sci. 2021 Mar 24;11(4):410. doi: 10.3390/brainsci11040410.
Slow-wave sleep (SWS) has been shown to promote long-term consolidation of episodic memories in hippocampo-neocortical networks. Previous research has aimed to modulate cortical sleep slow-waves and spindles to facilitate episodic memory consolidation. Here, we instead aimed to modulate hippocampal activity during slow-wave sleep using transcranial direct current stimulation in 18 healthy humans. A pair-associate episodic memory task was used to evaluate sleep-dependent memory consolidation with face-occupation stimuli. Pre- and post-nap retrieval was assessed as a measure of memory performance. Anodal stimulation with 2 mA was applied bilaterally over the lateral temporal cortex, motivated by its particularly extensive connections to the hippocampus. The participants slept in a magnetic resonance (MR)-simulator during the recordings to test the feasibility for a future MR-study. We used a sham-controlled, double-blind, counterbalanced randomized, within-subject crossover design. We show that stimulation vs. sham significantly increased slow-wave density and the temporal coupling of fast spindles and slow-waves. While retention of episodic memories across sleep was not affected across the entire sample of participants, it was impaired in participants with below-average pre-sleep memory performance. Hence, bi-temporal anodal direct current stimulation applied during sleep enhanced sleep parameters that are typically involved in memory consolidation, but it failed to improve memory consolidation and even tended to impair consolidation in poor learners. These findings suggest that artificially enhancing memory-related sleep parameters to improve memory consolidation can actually backfire in those participants who are in most need of memory improvement.
慢波睡眠（SWS）已被证明可促进海马体 - 新皮质网络中情景记忆的长期巩固。以往的研究旨在调节皮质睡眠慢波和纺锤波，以促进情景记忆巩固。在此，我们旨在通过对18名健康人进行经颅直流电刺激，在慢波睡眠期间调节海马体活动。使用配对联想情景记忆任务，通过面部 - 职业刺激来评估睡眠依赖的记忆巩固。午睡前后的记忆提取被评估为记忆表现的一种衡量指标。鉴于外侧颞叶皮质与海马体有特别广泛的连接，以2毫安的强度在双侧外侧颞叶皮质施加阳极刺激。在记录过程中，参与者在磁共振（MR）模拟器中睡眠，以测试未来进行MR研究的可行性。我们采用了假对照、双盲、平衡随机、受试者内交叉设计。我们发现，与假刺激相比，刺激显著增加了慢波密度以及快速纺锤波与慢波的时间耦合。虽然在所有参与者样本中，睡眠期间情景记忆的保持未受影响，但在睡眠前记忆表现低于平均水平的参与者中，情景记忆保持受到了损害。因此，睡眠期间双侧阳极直流电刺激增强了通常参与记忆巩固的睡眠参数，但未能改善记忆巩固，甚至在记忆较差的学习者中还往往会损害记忆巩固。这些发现表明，人为增强与记忆相关的睡眠参数以改善记忆巩固，实际上可能会在那些最需要改善记忆的参与者身上适得其反。
