Theta’s functional role in encoding, nocturnal reactivation and retrieval for the formationof declarative memory traces

我的研究目的是调查清醒和睡眠过程中记忆过程不同阶段的振荡theta活动的功能相关性。我们计划在荷兰-德国的单词对范式中测试在theta频段(theta-Tacs，6 Hz)范围内的经颅交流刺激对睡眠后记忆表现的影响，以探索编码前、夜间重新激活和提取之前theta活动可能的功能作用。我们假设，在编码(研究1)和提取(研究2)听觉和视觉呈现的物品之前进行的theta-Tacs将改变正在进行的大脑状态。以前的研究结果表明，编码前较高的theta对于改善延迟保持是必不可少的。因此，对于研究1，我们假设由模拟产生的更大的theta功率将导致第二天早上更好的保持性能。鉴于提取前的大脑状态和编码过程中的大脑状态一样重要，而且在尝试提取信息时，theta被认为是重要的，在研究2中，我们还预计这种刺激会产生更高的保持性能。一般来说，我们并不期望在应用Sham-Tacs之后内存性能会有所改善。考虑到听觉呈现的通道偏好，我们期望与视觉呈现的项目相比，听觉呈现的项目的结果通常更好。此外，关于语境依存性，我们还期望在回忆过程中以与研究阶段呈现相同的通道提示的项目具有更好的记忆性能。在研究3中，我们在夜间重新激活之前编码的项目(听觉和视觉呈现)之前不久应用了theta-Tacs，这是由我们诱导的。我们假设，与之前没有编码的项目相比，SWS期间听觉项目的重新激活通常会在睡眠后导致更好的保持性能。此外，由于仅在听觉夜间重新激活时的上下文相似性，我们期望声音呈现的项目比视觉呈现的项目具有更好的保持性能。额外的theta-Tacs(在重新激活一部分先前学习的项目之前应用)应该会导致相应频段中功率的增加，从而导致第二天早上比Sham-Tacs以及完全新的单词更好的保持性能。这样的结果可能是一个迹象，表明theta在改善重新激活的项目的记忆强度方面所起的作用。总体而言，这些结果可以提供关于theta频段在陈述性记忆形成过程中的潜在功能作用的见解。

The aim of my studies is to investigate the functional relevance of oscillatory theta activity during wakefulness and sleep in different stages of the memory process. We plan to test the influence of transcranial alternating current stimulation in the range of the theta frequency band (theta-tACS, 6 Hz) on the memory performance after sleep in a Dutch-German wordpair paradigm to explore a possible functional role of theta activity before encoding, nocturnal reactivation and retrieval. We hypothesize that theta-tACS conducted before encoding (study 1) as well as retrieval (study 2) of acoustically and visually presented items will modify the ongoing brain state. Previous findings revealed that higher theta before encoding is essential for an improved delayed retention. Therefore, we assume for study 1 that the increased theta power resulting from the simulation will lead to a better retention performance the next morning. Given that the brain state before retrieval is as important as during encoding and that theta is seen as important in the attempt of retrieving information, for study 2 we also expect a higher retention performance resulting from such a stimulation. In general, we do not expect an improvement in memory performance after applying sham-tACS. Given the modality preference for auditory presentation we expect a generally better result for acoustically presented items compared to visually presented items. Additionally, with regard to the context dependency we also expect a better memory performance for items which are cued during recall in the same modality as they are presented during the study phase. In study 3 we apply theta-tACS shortly before the nocturnal reactivation of previously encoded items (auditory and visually presented) which is induced by us. We assume that auditory item reactivation during SWS leads generally to an improved retention performance after sleep compared to items which are not encoded previously. Additionally, we expect a better retention performance of acoustically presented items compared to visually presented items due to the context similarity during only auditory nocturnal reactivation. The additional theta-tACS (applied before reactivation of a part of the previously learned items) should lead to an increase in power in the respective frequency band and thus, result in better retention performance the next morning compared to sham-tACS as well as completely new words. Such a result could be an indication for the role theta is playing in improving the memory strength of reactivated items. In general, the results could provide insights about a potential functional role of the theta frequency band for formation processes of declarative memories.