State-dependent signal flow hierarchy in the human cerebral cortex
The signal-flow hierarchy that I recovered from fMRI aligned significantly with the cortical hierarchy proposed by M. Mesulam in his textbook Principles of Behavioral and Cognitive Neurology, which was used in the seminal paper by Margulies et al. (2016) to define the “functional hierarchy.” However, that was an implicit hierarchy with no defined direction, and it was ambiguous about the role of the paralimbic cortex. Furthermore, my signal-flow hierarchy showed the quintessential nature of flexibility in the brain by demonstrating state-dependent changes. Importantly, the overall structure of the hierarchy (the ordering from the most external to the most internal) did not change, indicating the universal role of internally driven top-down modulation of external signals. If you are interested in learning more, click below for the full text.