Table_3_The Brain in (Willed) Action: A Meta-Analytical Comparison of Imaging Studies on Motor Intentionality and Sense of Agency.docx

Voluntary actions can be fractionated in different phenomena: from the emergence of intentions and the ensuing motor plans and actions, to the anticipation and monitoring of their outcomes, to the appreciation of their congruency with intentions and to the eventual emergence of a sense of agency. It follows that motor intention and the sense of agency should occur at different stages in the normal generation of willed actions. Both these processes have been associated with a fronto-parietal motor network, but no study has investigated to what extent the two experiences can be dissociated for the brain regions involved. To this end, we assessed the PET/fMRI literature on agency and intentionality using a meta-analytic technique based on a hierarchical clustering algorithm. Beside a shared brain network involving the meso-frontal and prefrontal regions, the middle insula and subcortical structures, we found that motor intention and the sense of agency are functionally underpinned by separable sets of brain regions: an “intentionality network,” involving the rostral area of the mesial frontal cortex (middle cingulum and pre-supplementary motor area), the anterior insula and the parietal lobules, and a “self-agency network,” which involves the posterior areas of the mesial frontal cortex (the SMA proper), the posterior insula, the occipital lobe and the cerebellum. We were then able to confirm this functional organization by a subsequent seed-based fMRI resting-state functional connectivity analysis, with seeds derived from the intentionality/sense of agency specific clusters of the medial wall of the frontal lobe. Our results suggest the existence of a rostro-caudal gradient within the mesial frontal cortex, with the more anterior regions linked to the concept of motor intentionality and the brain areas located more posteriorly associated with the direct monitoring between the action and its outcome. This suggestion is reinforced by the association between the sense of agency and the activation of the occipital lobes, to suggest a direct comparison between the movement and its external (e.g., visual) consequences. The shared network may be important for the integration of intentionality and agency in a coherent appreciation of self-generated actions.自主行为可被拆解为一系列连续的过程：从意图的萌生、随之而来的运动计划与动作执行，到对行为结果的预期与监控，再到评估其与初始意图的一致性，最终产生主体感（sense of agency）。由此可见，在意志驱动行为的正常生成过程中，运动意图与主体感会出现在不同的阶段。这两种加工过程均与额顶运动网络（fronto-parietal motor network）相关，但目前尚无研究探讨这两种主观体验在相关脑区上的分离程度。为此，我们采用基于层次聚类算法的元分析技术，对有关主体感与意向性（intentionality）的PET/fMRI相关文献进行了系统梳理。除了包含中额叶、前额叶区域、岛叶中部以及皮层下结构的共享脑网络外，我们发现运动意图与主体感在功能上由不同的脑区集合所支撑：其一为"intentionality network"，涉及内侧额叶皮层的嘴侧区域（中扣带回与前辅助运动区（pre-supplementary motor area））、前岛叶与顶叶小叶；其二为"self-agency network"，涉及内侧额叶皮层的后部区域（辅助运动区本体（SMA proper））、后岛叶、枕叶与小脑。随后，我们通过基于种子点的fMRI静息态功能连接分析，以取自额叶内侧壁上与意向性/主体感特异性相关的聚类脑区作为种子点，进一步验证了这一功能组织模式。我们的研究结果表明，内侧额叶皮层内存在一条嘴尾侧梯度：越靠前的区域与运动意向性的概念加工相关，而越靠后的脑区则与行为及其结果之间的直接监控过程相关。主体感与枕叶激活之间的关联进一步佐证了这一观点，提示大脑会对运动行为与其外部（如视觉）后果进行直接比对。二者共享的脑网络可能对于将意向性与主体感整合为对自我生成行为的连贯认知具有重要意义。