Donders Centre for Neuroscience, Radboud University, 6525 AJ Nijmegen, The Netherlands.
Radiology Department, University of California at San Francisco, San Francisco, California 94143.
J Neurosci. 2020 Sep 30;40(40):7702-7713. doi: 10.1523/JNEUROSCI.0321-20.2020. Epub 2020 Sep 8.
Theta-band (∼6 Hz) rhythmic activity within and over the medial PFC ("midfrontal theta") has been identified as a distinctive signature of "response conflict," the competition between multiple actions when only one action is goal-relevant. Midfrontal theta is traditionally conceptualized and analyzed under the assumption that it is a unitary signature of conflict that can be uniquely identified at one electrode (typically FCz). Here we recorded simultaneous MEG and EEG (total of 328 sensors) in 9 human subjects (7 female) and applied a feature-guided multivariate source-separation decomposition to determine whether conflict-related midfrontal theta is a unitary or multidimensional feature of the data. For each subject, a generalized eigendecomposition yielded spatial filters (components) that maximized the ratio between theta and broadband activity. Components were retained based on significance thresholding and midfrontal EEG topography. All of the subjects individually exhibited multiple (mean 5.89, SD 2.47) midfrontal components that contributed to sensor-level midfrontal theta power during the task. Component signals were temporally uncorrelated and asynchronous, suggesting that each midfrontal theta component was unique. Our findings call into question the dominant notion that midfrontal theta represents a unitary process. Instead, we suggest that midfrontal theta spans a multidimensional space, indicating multiple origins, but can manifest as a single feature at the sensor level because of signal mixing. "Midfrontal theta" is a rhythmic electrophysiological signature of the competition between multiple response options. Midfrontal theta is traditionally considered to reflect a single process. However, this assumption could be erroneous because of "mixing" (multiple sources contributing to the activity recorded at a single electrode). We investigated the dimensionality of midfrontal theta by applying advanced multivariate analysis methods to a multimodal MEG/EEG dataset. We identified multiple topographically overlapping neural sources that drove response conflict-related midfrontal theta. Midfrontal theta thus reflects multiple uncorrelated signals that manifest with similar EEG scalp projections. In addition to contributing to the cognitive control literature, we demonstrate both the feasibility and the necessity of signal demixing to understand the narrowband neural dynamics underlying cognitive processes.
θ 波段（∼6 Hz）在中前额皮质（“前额中部 θ”）内和上方的节律性活动已被确定为“反应冲突”的独特特征，即当只有一个动作与目标相关时，多个动作之间的竞争。前额中部 θ 通常是在假设它是冲突的单一特征的情况下进行概念化和分析的，这种冲突可以在一个电极（通常是 FCz）上唯一识别。在这里，我们在 9 名人类受试者（7 名女性）中同时记录了 MEG 和 EEG（共 328 个传感器），并应用了特征引导的多元源分离分解来确定与冲突相关的前额中部 θ 是否是数据的单一或多维特征。对于每个受试者，广义特征分解产生了最大化θ与宽带活动之间比值的空间滤波器（分量）。根据显著性阈值和前额中部 EEG 拓扑结构保留分量。所有受试者个体表现出多个（平均 5.89，标准差 2.47）前额中部分量，这些分量在前额中部 θ 功率在任务期间对传感器级别的贡献。分量信号在时间上是不相关和异步的，这表明每个前额中部 θ 分量都是独特的。我们的发现对主导观念提出了质疑，即前额中部 θ 代表单一过程。相反，我们认为前额中部 θ 跨越多维空间，表明有多个起源，但由于信号混合，可能在传感器水平上表现为单一特征。“前额中部 θ”是多个反应选项之间竞争的节律性电生理特征。前额中部 θ 传统上被认为反映了单个过程。然而，由于“混合”（多个源对单个电极记录的活动有贡献），这种假设可能是错误的。我们通过将先进的多元分析方法应用于多模态 MEG/EEG 数据集，来研究前额中部 θ 的维度。我们确定了多个拓扑重叠的神经源，这些神经源驱动了与反应冲突相关的前额中部 θ。因此，前额中部 θ 反映了多个不相关的信号，这些信号以类似的 EEG 头皮投影表现出来。除了对认知控制文献做出贡献外，我们还展示了信号解混的可行性和必要性，以了解认知过程背后的窄带神经动力学。
