Multimodal connectivity-based parcellation reveals a shell-core dichotomy of the human nucleus accumbens

The subdifferentiation of the nucleus accumbens (NAc) has been extensively studied using neuroanatomy and histochemistry, yielding a well-accepted dichotomic shell/core architecture that reflects dissociable roles, such as in reward and aversion, respectively. However, in vivo parcellation of these structures in humans has been rare, potentially impairing future research into the structural and functional characteristics and alterations of putative NAc subregions. Here, we used three complementary parcellation schemes based on tractography, task-independent functional connectivity, and task-dependent co-activation to investigate the regional differentiation within the NAc. We found that a 2-cluster solution with shell-like and core-like subdivisions provided the best description of the data and was consistent with the earlier anatomical shell/core architecture. The consensus clusters from this optimal solution, which was based on the three schemes, were used as the final parcels for the subsequent connection analyses. The resulting connectivity patterns presented inter-hemispheric symmetry, convergence and divergence across the modalities, and, most importantly, clearly distinct patterns between the two subregions. This convergent connectivity patterns also confirmed the connections in animal models, supporting views that the two subregions could have antagonistic roles in some circumstances. Finally, the identified parcels should be helpful in further neuroimaging studies of the NAc.

伏隔核（nucleus accumbens, NAc）的亚分区研究已通过神经解剖学与组织化学方法得到广泛开展，目前已形成广为接受的二分法壳/核结构架构，该架构对应功能可分离的不同作用，例如分别参与奖赏与厌恶处理。然而，针对人类个体的这些结构的活体分区研究却较为稀缺，这可能会阻碍未来针对伏隔核亚区的结构与功能特征及其异常改变开展的相关研究。本研究采用基于纤维束追踪术（tractography）、任务无关功能连接（task-independent functional connectivity）以及任务依赖共激活（task-dependent co-activation）的三种互补性分割方案，对伏隔核内部的区域分化特征进行探究。研究结果显示，包含壳样与核样亚分区的两聚类方案能够最优地拟合数据集，且与此前报道的解剖学壳/核结构架构相一致。基于这三种分割方案得到的最优聚类的一致性亚区，被用作后续连接分析的最终脑区分割单元。所得的连接模式呈现出半球间对称性，且在不同模态间存在汇聚与分化；最为关键的是，两个亚区之间的连接模式存在显著差异。这种一致性的连接模式也验证了动物模型中的相关连接发现，支持了“两个亚区在特定情境下可能具有拮抗性功能”的学术观点。本研究确定的亚区分割单元将有助于伏隔核相关的后续神经影像学研究。