Situating the default-mode network in a principal gradient of macroscale cortical organization

Understanding how the structure of cognition arises from the to- pographical organization of the cortex is a primary goal in neuroscience. Previous work has described local functional gradients extending from perceptual and motor regions to cortical areas representing more abstract functions, yet an overarching framework for the association between structure and function is still lacking. Here we show that the principal gradient revealed by the decomposition of connectivity data in humans and the macaque monkey is anchored, at one end, by regions serving primary sensory/motor functions and, at the other, by transmodal regions that, in humans, are known as the default-mode network (DMN). These DMN regions exhibit the greatest geodesic distance along the cortical surface — and are precisely equidistant — from primary sensory/motor morphological landmarks. The principal gradient also provides an organizing spatial framework for multiple large-scale networks and characterizes a spectrum from unimodal to heteromodal activity in a functional meta-analysis. Together these observations provide a novel characterization of the topographical organization of cortex and indicate that the role of the DMN in cognition might arise from its position at one extreme of a hierarchy, allowing it to process transmodal information that is unrelated to immediate sensory input