Max Planck Research Group Auditory Cognition, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany,
Experimental Psychology Laboratory, Center for Excellence Hearing4all, European Medical School, University of Oldenburg, 26111 Oldenburg, Germany.
J Neurosci. 2018 Aug 22;38(34):7428-7439. doi: 10.1523/JNEUROSCI.2928-17.2018. Epub 2018 Jul 16.
Increased memory load is often signified by enhanced neural oscillatory power in the alpha range (8-13 Hz), which is taken to reflect inhibition of task-irrelevant brain regions. The corresponding neural correlates of memory decay, however, are not yet well understood. In the current study, we investigated auditory short-term memory decay in humans using a delayed matching-to-sample task with pure-tone sequences. First, in a behavioral experiment, we modeled memory performance over six different delay-phase durations. Second, in a MEG experiment, we assessed alpha-power modulations over three different delay-phase durations. In both experiments, the temporal expectation for the to-be-remembered sound was manipulated so that it was either temporally expected or not. In both studies, memory performance declined over time, but this decline was weaker when the onset time of the to-be-remembered sound was expected. Similarly, patterns of alpha power in and alpha-tuned connectivity between sensory cortices changed parametrically with delay duration (i.e., decrease in occipitoparietal regions, increase in temporal regions). Temporal expectation not only counteracted alpha-power decline in heteromodal brain areas (i.e., supramarginal gyrus), but also had a beneficial effect on memory decay, counteracting memory performance decline. Correspondingly, temporal expectation also boosted alpha connectivity within attention networks known to play an active role during memory maintenance. The present data show how patterns of alpha power orchestrate short-term memory decay and encourage a more nuanced perspective on alpha power across brain space and time beyond its inhibitory role. Our sensory memories of the physical world fade quickly. We show here that this decay of short-term memory can be counteracted by so-called temporal expectation; that is, knowledge of when to expect a sensory event that an individual must remember. We also show that neural oscillations in the "alpha" (8-13 Hz) range index both the degree of memory decay (for brief sound patterns) and the respective memory benefit from temporal expectation. Spatially distributed cortical patterns of alpha power show opposing effects in auditory versus visual sensory cortices. Moreover, alpha-tuned connectivity changes within supramodal attention networks reflect the allocation of neural resources as short-term memory representations fade.
记忆负荷增加通常表现为 alpha 频段（8-13Hz）的神经振荡功率增强，这被认为反映了对任务无关脑区的抑制。然而，记忆衰退的相应神经相关物尚不清楚。在当前的研究中，我们使用纯音序列的延迟匹配样本任务来研究人类的听觉短期记忆衰退。首先，在行为实验中，我们对六个不同延迟阶段持续时间的记忆表现进行建模。其次，在 MEG 实验中，我们评估了三个不同延迟阶段持续时间的 alpha 功率调制。在两个实验中，我们操纵了待记忆声音的时间期望，使其具有时间可预测性或不可预测性。在两个研究中，记忆表现随时间推移而下降，但当要记住的声音的起始时间可预测时，这种下降较弱。同样，感觉皮层的 alpha 功率模式和 alpha 调谐连接也随延迟持续时间呈参数变化（即枕顶区域减少，颞区域增加）。时间期望不仅抵消了异模态大脑区域（即缘上回）的 alpha 功率下降，而且对记忆衰退也有有益影响，抵消了记忆表现的下降。相应地，时间期望也增强了已知在记忆维持过程中起积极作用的注意网络内的 alpha 连接。本研究数据表明，alpha 功率模式如何协调短期记忆衰退，并鼓励在大脑空间和时间上对 alpha 功率进行更细致的观察，超越其抑制作用。我们对物理世界的感官记忆很快就会消逝。我们在这里表明，这种短期记忆的衰退可以通过所谓的时间期望来抵消；也就是说，当个体必须记住某个感官事件时，知道何时可以期待该感官事件。我们还表明，alpha 频段（8-13Hz）的神经振荡不仅可以指示记忆衰退的程度（对于短暂的声音模式），还可以指示来自时间期望的相应记忆收益。听觉与视觉感觉皮层中 alpha 功率的空间分布模式表现出相反的效果。此外，超模态注意网络内的 alpha 调谐连接变化反映了短期记忆表示消退时神经资源的分配。
