Berenson-Allen Center for Noninvasive Brain Stimulation, and Division of Cognitive Neurology, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
Proc Natl Acad Sci U S A. 2011 Dec 27;108(52):21229-34. doi: 10.1073/pnas.1113103109. Epub 2011 Dec 12.
Intrinsic activity in the brain is organized into networks. Although constrained by their anatomical connections, functional correlations between nodes of these networks reorganize dynamically. Dynamic organization implies that couplings between network nodes can be reconfigured to support processing demands. To explore such reconfigurations, we combined repetitive transcranial magnetic stimulation (rTMS) and functional connectivity MRI (fcMRI) to modulate cortical activity in one node of the default network, and assessed the effect of this upon functional correlations throughout the network. Two different frequencies of rTMS to the same default network node (the left posterior inferior parietal lobule, lpIPL) induced two topographically distinct changes in functional connectivity. High-frequency rTMS to lpIPL decreased functional correlations between cortical default network nodes, but not between these nodes and the hippocampal formation. In contrast, low frequency rTMS to lpIPL did not alter connectivity between cortical default network nodes, but increased functional correlations between lpIPL and the hippocampal formation. These results suggest that the default network is composed of (at least) two subsystems. More broadly, the finding that two rTMS stimulation regimens to the same default network node have distinct effects reveals that this node is embedded within a network that possesses multiple, functionally distinct relationships among its distributed partners.
大脑的内在活动组织成网络。尽管受到解剖连接的限制，但这些网络节点之间的功能相关性会动态地重新组织。动态组织意味着网络节点之间的耦合可以重新配置以支持处理需求。为了探索这种重新配置，我们结合重复经颅磁刺激（rTMS）和功能连接 MRI（fcMRI）来调节默认网络中的一个节点的皮质活动，并评估这种刺激对整个网络功能相关性的影响。针对同一默认网络节点（左侧后下顶叶 lobule，lpIPL）施加两种不同频率的 rTMS，会导致功能连接发生两种截然不同的拓扑变化。高频 rTMS 刺激 lpIPL 会降低皮质默认网络节点之间的功能相关性，但不会降低这些节点与海马结构之间的功能相关性。相比之下，低频 rTMS 刺激 lpIPL 不会改变皮质默认网络节点之间的连接，但会增加 lpIPL 与海马结构之间的功能相关性。这些结果表明，默认网络由（至少）两个子系统组成。更广泛地说，发现同一默认网络节点的两种 rTMS 刺激方案具有不同的效果，这表明该节点嵌入在一个网络中，该网络在其分布式伙伴之间具有多种不同的功能关系。
