Certain organizational features of brain networks present in the individual are lost when central tendencies are examined in the group. Here we investigated the detailed network organization of four individuals each scanned 24 times using MRI. We discovered that the distributed network known as the default network is comprised of two separate networks possessing adjacent regions in eight or more cortical zones. A distinction between the networks is that one is coupled to the hippocampal formation while the other is not. Further exploration revealed that these two networks were juxtaposed with additional networks that themselves fractionate group-defined networks. The collective networks display a repeating spatial progression in multiple cortical zones, suggesting that they are embedded within a broad macroscale gradient. Regions contributing to the newly defined networks are spatially variable across individuals and adjacent to distinct networks, raising issues for network estimation in group-averaged data and applied endeavors, including targeted neuromodulation.

Introduction

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Motivated by these findings, we conducted an extensive set of analyses focused on the individual. We discovered that the DN could be reliably subdivided into parallel networks within the individual. Similar separations were made for other major networks. Regions of the separate networks lay side by side across distributed zones of cortex and were sufficiently variable between individuals to obscure their existence in group-averaged analyses. To make these observations, we analyzed data from four individuals scanned repeatedly over 24 sessions.