title: The trees and the forest: Characterization of complex brain networks with minimum spanning trees.
abstract: In recent years there has been a shift in focus from the study of local, mostly task-related activation to the exploration of the organization and functioning of large-scale structural and functional complex brain networks. Progress in the interdisciplinary field of modern network science has introduced many new concepts, analytical tools and models which allow a systematic interpretation of multivariate data obtained from structural and functional MRI, EEG and MEG. However, progress in this field has been hampered by the absence of a simple, unbiased method to represent the essential features of brain networks, and to compare these across different conditions, behavioural states and neuropsychiatric/neurological diseases. One promising solution to this problem is to represent brain networks by a minimum spanning tree (MST), a unique acyclic subgraph that connects all nodes and maximizes a property of interest such as synchronization between brain areas. We explain how the global and local properties of an MST can be characterized. We then review early and more recent applications of the MST to EEG and MEG in epilepsy, development, schizophrenia, brain tumours, multiple sclerosis and Parkinson's disease, and show how MST characterization performs compared to more conventional graph analysis. Finally, we illustrate how MST characterization allows representation of observed brain networks in a space of all possible tree configurations and discuss how this may simplify the construction of simple generative models of normal and abnormal brain network organization.
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: CJ.Stam@VUmc.nl.
authors.forename: C J
authors.initials: CJ
authors.lastname: Stam
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Tewarie
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands; Department of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Van Dellen
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: E C W
authors.initials: EC
authors.lastname: van Straaten
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Hillebrand
authors.affiliation: Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, PO Box 5031, 2600 GA, Delft, The Netherlands. Electronic address: P.F.A.VanMieghem@tudelft.nl.
authors.forename: P
authors.initials: P
authors.lastname: Van Mieghem
mesh_terms: D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D006801:Humans; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*
keywords: Brain networks; EEG; Functional connectivity; Graph theory; MEG; Minimum spanning tree