Ryyppö Elisa, Glerean Enrico, Brattico Elvira, Saramäki Jari, Korhonen Onerva
Department of Computer Science, School of Science, Aalto University, Espoo, Finland.
Turku PET Centre, University of Turku, Turku, Finland.
Netw Neurosci. 2018 Oct 1;2(4):513-535. doi: 10.1162/netn_a_00047. eCollection 2018.
The properties of functional brain networks strongly depend on how their nodes are chosen. Commonly, nodes are defined by Regions of Interest (ROIs), predetermined groupings of fMRI measurement voxels. Earlier, we demonstrated that the functional homogeneity of ROIs, captured by their , varies widely across ROIs in commonly used brain atlases. Here, we ask how ROIs behave as nodes of dynamic brain networks. To this end, we use two measures: measures changes in spatial consistency across time and quantifies the changes in the local network structure around an ROI. We find that spatial consistency varies non-uniformly in space and time, which is reflected in the variation of spatiotemporal consistency across ROIs. Furthermore, we see time-dependent changes in the network neighborhoods of the ROIs, reflected in high network turnover. Network turnover is nonuniformly distributed across ROIs: ROIs with high spatiotemporal consistency have low network turnover. Finally, we reveal that there is rich voxel-level correlation structure inside ROIs. Because the internal structure and the connectivity of ROIs vary in time, the common approach of using static node definitions may be surprisingly inaccurate. Therefore, network neuroscience would greatly benefit from node definition strategies tailored for dynamical networks.
功能性脑网络的属性在很大程度上取决于其节点的选择方式。通常，节点由感兴趣区域（ROI）定义，即功能磁共振成像（fMRI）测量体素的预先确定的分组。此前，我们证明了ROI的功能同质性，由其[此处缺失具体内容]捕获，在常用脑图谱中的不同ROI之间差异很大。在这里，我们研究ROI作为动态脑网络节点的行为方式。为此，我们使用两种测量方法：[此处缺失具体内容]测量空间一致性随时间的变化，[此处缺失具体内容]量化ROI周围局部网络结构的变化。我们发现空间一致性在空间和时间上非均匀变化，这反映在不同ROI的时空一致性变化中。此外，我们看到ROI的网络邻域随时间变化，表现为高网络周转率。网络周转率在不同ROI之间分布不均匀：时空一致性高的ROI网络周转率低。最后，我们揭示ROI内部存在丰富的体素级相关结构。由于ROI的内部结构和连通性随时间变化，使用静态节点定义的常见方法可能出人意料地不准确。因此，网络神经科学将从为动态网络量身定制的节点定义策略中受益匪浅。
