Interactions between hippocampus, prefrontal cortex and visual association cortex during short-term memory maintenance

视觉短时记忆(STM)指的是视觉信息在短时间间隔内的维持。视觉STM的关键脑区包括前额叶皮质和顶枕区。此外，越来越多的证据表明，当需要维持多个项目时，海马会被招募；然而，海马区、前额叶皮质和顶枕区的STM相关机制是否以及如何相互关联仍不清楚。特定项目的维护可以通过多变量模式分类分析(MVPA)进行调查，该分析既适用于EEG数据，也适用于fMRI数据。然而，以前没有研究研究STM过程中多个项目的刺激特异性重新激活。此外，尚不清楚海马体和前额叶皮质是否以及如何与支持刺激特定表征的区域相互作用，以及它们是否控制这些表征。在这里，我们将解决这些悬而未决的问题。根据一个有影响力的计算机模型，STM依赖于多路传输缓冲器，在该多路传输缓冲器中，在theta(3-8赫兹)频率范围内的神经振荡的后续相位范围期间，项目被连续地重新激活。具体地说，我们将测试这一假设，即海马体和/或前额叶皮质通过与视觉关联区中分布的活动模式的振荡相互作用来控制特定项目的表征。我们将调查两组参与者：一组为手术计划植入了海马区和/或新皮质脑电(IEEG)电极的癫痫患者，另一组是同时接受EEG/fMRI检查的健康参与者。将使用MVPA对iEEG数据(在iEEG实验中)和头皮EEG数据(在同时进行的EEG/fMRI实验中)进行刺激特定表征的评估。同时，将使用健康参与者的海马区iEEG或fMRI记录来分析海马区的激活情况。这个项目将有助于阐明视觉STM背后的神经机制，以及海马体在多项目STM中的作用。

Visual short-term memory (STM) refers to the maintenance of visual information for a short time interval. Key brain regions of visual STM include the prefrontal cortex and parietooccipital regions. Furthermore, increasing evidence suggests that the hippocampus is recruited when multiple items need to be maintained; however, it is still unclear if and how STM-related mechanisms in hippocampus, prefrontal cortex and parietooccipital regions are interrelated. Maintenance of specific items can be investigated by multivariate pattern classification analyses (MVPA) which can be applied to both EEG and fMRI data. However, no previous study has investigated stimulus-specific reactivation of multiple items during STM. Furthermore, it is unknown if and how hippocampus and prefrontal cortex interact with regions supporting stimulus-specific representations, and if they control these representations. Here, we will address these open questions. According to an influential computer model, STM depends on a multiplexing buffer in which items are consecutively reactivated during subsequent phase ranges of neural oscillations in the theta (3-8 Hz) frequency range. Specifically, we will thus test the hypothesis that hippocampus and/or prefrontal cortex control representations of specific items via oscillatory interactions with distributed activity patterns in visual association areas. We will investigate two groups of participants: Presurgical epilepsy patients who are implanted with hippocampal and/or neocortical intracranial EEG (iEEG) electrodes for planning of resective surgery, and healthy participants undergoing simultaneous EEG/fMRI. Stimulus-specific representations will be assessed using MVPA on iEEG data (in the iEEG experiment) and on scalp EEG data (in the simultaneous EEG/fMRI experiment). Simultaneously, hippocampal activation will be analyzed using either iEEG from the hippocampus or fMRI recordings in the healthy participants. This project will help clarifying the neural mechanisms underlying visual STM and the role of the hippocampus for multi-item STM.