Homological scaffolds of brain functional  networks.
Networks, as efficient representations of complex systems, have appealed to scientists for a long time and now permeate many areas of science, including neuroimaging (Bullmore and Sporns 2009 Nat. Rev. Neurosci. 10, 186-198. (doi:10.1038/nrn2618)). Traditionally, the structure of complex networks has been studied through their statistical properties and metrics concerned with node and link properties, e.g. degree-distribution, node centrality and modularity. Here, we study the characteristics of functional brain networks at the mesoscopic level from a novel perspective that highlights the role of inhomogeneities in the fabric of functional connections. This can be done by focusing on the features of a set of topological objects-homological cycles-associated with the weighted functional network. We leverage the detected topological information to define the homological scaffolds, a new set of objects designed to represent compactly the homological features of the correlation network and simultaneously make their homological properties amenable to networks theoretical methods. As a proof of principle,we apply these tools to compare resting state functional brain activity in 15 healthy volunteers after intravenous infusion of placebo and psilocybin-the main psychoactive component of magic mushrooms. The results show that the homological structure of the brain's functional patterns undergoes a dramatic change post-psilocybin, characterized by the appearance of many transient structures of low stability and of a small number of persistent ones that are not observed in the case of placebo.
G
G
Petri
P
P
Expert
F
F
Turkheimer
R
R
Carhart-Harris
D
D
Nutt
P J
PJ
Hellyer
F
F
Vaccarino
D001921:Brain / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006213:Hallucinogens / Q000008:administration & dosage; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D011562:Psilocybin / Q000008:administration & dosage; D011859:Radiography
D006213:Hallucinogens; D011562:Psilocybin