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Trends Cogn Sci. 2013 Dec;17(12):648-65. doi: 10.1016/j.tics.2013.09.017. Epub 2013 Nov 7.

The evolution of distributed association networks in the human brain.

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Harvard University Department of Psychology, Center for Brain Science, Cambridge, MA, USA; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA; Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA. Electronic address:


The human cerebral cortex is vastly expanded relative to other primates and disproportionately occupied by distributed association regions. Here we offer a hypothesis about how association networks evolved their prominence and came to possess circuit properties vital to human cognition. The rapid expansion of the cortical mantle may have untethered large portions of the cortex from strong constraints of molecular gradients and early activity cascades that lead to sensory hierarchies. What fill the gaps between these hierarchies are densely interconnected networks that widely span the cortex and mature late into development. Limitations of the tethering hypothesis are discussed as well as its broad implications for understanding critical features of the human brain as a byproduct of size scaling.


cerebellum; cortical circuits; default network; prefrontal cortex; prospection; social cognition

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