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

视觉短期记忆（STM）是指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层和顶叶枕区。此外，越来越多的证据表明，当需要维持多个项目时，海马体会被招募；然而，海马体、前额叶皮层和顶叶枕区的stm相关机制是否相互关联以及如何相互关联尚不清楚。特定项目的维持可以通过多变量模式分类分析（MVPA）进行调查，该分析可以应用于脑电图和功能磁共振成像数据。然而，之前没有研究调查了在STM过程中多个项目的刺激特异性再激活。此外，尚不清楚海马体和前额皮质是否以及如何与支持刺激特异性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依赖于一个多路复用缓冲器，在该缓冲器中，在θ (3-8 Hz)频率范围内的神经振荡的后续相位范围内，项目被连续重新激活。具体来说，我们将因此测试海马体和/或前额皮质通过与视觉关联区域的分布式活动模式的振荡相互作用来控制特定项目表征的假设。我们将研究两组参与者：手术前植入海马和/或新皮层颅内脑电图（iEEG）电极以计划切除手术的癫痫患者，以及同时进行EEG/fMRI的健康参与者。刺激特异性表征将在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）上使用MVPA进行评估。同时，使用海马体的iEEG或功能磁共振成像记录来分析健康参与者的海马体激活情况。本项目将有助于阐明视觉STM的神经机制以及海马在多项目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.