Imperial College London

Dr Peter Hellyer

Faculty of MedicineDepartment of Brain Sciences

Honorary Lecturer



+44 (0)20 7594 9568peter.hellyer




4.35Royal School of MinesSouth Kensington Campus






BibTex format

author = {Petri, G and Expert, P and Turkheimer, F and Carhart-Harris, R and Nutt, D and Hellyer, PJ and Vaccarino, F},
doi = {10.1098/rsif.2014.0873},
journal = {Journal of the Royal Society Interface},
title = {Homological scaffolds of brain functional networks},
url = {},
volume = {11},
year = {2014}

RIS format (EndNote, RefMan)

AB - Networks, as efficient representations of complex systems, have appealed toscientists for a long time and now permeate many areas of science, includingneuroimaging (Bullmore and Sporns 2009 Nat. Rev. Neurosci. 10, 186–198.(doi:10.1038/nrn2618)). Traditionally, the structure of complex networks hasbeen studied through their statistical properties and metrics concerned withnode and link properties, e.g. degree-distribution, node centrality and modularity.Here, we study the characteristics of functional brain networks at themesoscopic level from a novel perspective that highlights the role of inhomogeneitiesin the fabric of functional connections. This can be done by focusingon the features of a set of topological objects—homological cycles—associatedwith the weighted functional network. We leverage the detected topologicalinformation to define the homological scaffolds, a new set of objects designed torepresent compactly the homological features of the correlation network andsimultaneously make their homological properties amenable to networks theoreticalmethods. As a proof of principle, we apply these tools to compare restingstatefunctional brain activity in 15 healthy volunteers after intravenous infusionof placebo and psilocybin—the main psychoactive component of magic mushrooms.The results show that the homological structure of the brain’s functionalpatterns undergoes a dramatic change post-psilocybin, characterized by theappearance of many transient structures of low stability and of a smallnumber of persistent ones that are not observed in the case of placebo.
AU - Petri,G
AU - Expert,P
AU - Turkheimer,F
AU - Carhart-Harris,R
AU - Nutt,D
AU - Hellyer,PJ
AU - Vaccarino,F
DO - 10.1098/rsif.2014.0873
PY - 2014///
SN - 1742-5689
TI - Homological scaffolds of brain functional networks
T2 - Journal of the Royal Society Interface
UR -
UR -
VL - 11
ER -