Frontal-to-Parietal Top-Down Causal Streams along the Dorsal Attention Network Exclusively Mediate Voluntary Orienting of Attention

Previous effective connectivity analyses of functional magnetic resonance imaging (fMRI) have revealed dynamic causal streams along the dorsal attention network (DAN) during voluntary attentional control in the human brain. During resting state, however, fMRI has shown that the DAN is also intrinsically configured by functional connectivity, even in the absence of explicit task demands, and that may conflict with effective connectivity studies. To resolve this contradiction, we performed an effective connectivity analysis based on partial Granger causality (pGC) on event-related fMRI data during Posner's cueing paradigm while optimizing experimental and imaging parameters for pGC analysis. Analysis by pGC can factor out exogenous or latent influences due to unmeasured variables. Typical regions along the DAN with greater activation during orienting than withholding of attention were selected as regions of interest (ROIs). pGC analysis on fMRI data from the ROIs showed that frontal-to-parietal top-down causal streams along the DAN appeared during (voluntary) orienting, but not during other, less-attentive and/or resting-like conditions. These results demonstrate that these causal streams along the DAN exclusively mediate voluntary covert orienting. These findings suggest that neural representations of attention in frontal regions are at the top of the hierarchy of the DAN for embodying voluntary attentional control.

既往针对功能磁共振成像（functional magnetic resonance imaging, fMRI）的有效连接分析已证实，人脑在执行自主注意控制任务时，背侧注意网络（dorsal attention network, DAN）内存在动态因果信息流。然而，静息态fMRI研究表明，即便在无明确任务要求的情况下，背侧注意网络也可通过功能连接形成固有拓扑结构，该结论或与现有有效连接研究的结果存在冲突。为解决这一矛盾，本研究基于偏格兰杰因果关系（partial Granger causality, pGC），对波斯纳线索提示范式（Posner's cueing paradigm）下的事件相关fMRI数据开展有效连接分析，并针对pGC分析优化了实验设计与成像参数。偏格兰杰因果关系分析可有效排除未测量变量引发的外源性或潜在混杂影响。本研究选取背侧注意网络中，注意定向阶段激活程度显著高于注意抑制阶段的典型脑区作为感兴趣区（regions of interest, ROIs）。对上述感兴趣区的fMRI数据开展pGC分析后发现，背侧注意网络内的额-顶叶自上而下因果信息流仅在（自主）注意定向阶段出现，而在其他注意力水平较低或类静息态的实验条件下未观测到该信息流。上述结果证实，背侧注意网络的此类因果信息流仅介导自主隐蔽注意定向过程。本研究结果提示，额叶区域的注意神经表征处于背侧注意网络层级结构的顶层，负责实现自主注意控制功能。