Investigating brain community structure abnormalities in bipolar disorder using PLACE (Path Length Associated Community Estimation) Johnson J. GadElkarim* 1, 2 , Olusola Ajilore 2 , Dan Schonfeld 1 , Liang Zhan 3 , Paul M. Thomspon 3 Jamie D. Feusner 4 , Anand Kumar 2 , Lori L. Altshuler 4 , and Alex D. Leow* 2, 5 1 Electrical and Computer Engineering department, University of Illinois at Chicago 2 Department of Psychiatry, University of Illinois at Chicago 3 Laboratory of Neuro Imaging, UCLA School of Medicine 4 Department of Psychiatry and Behavioral Sciences, UCLA 5 Community Psychiatry, Sacramento, CA jgadel2@uic.edu, alexfeuillet@gmail.com Corresponding author: Alex Leow, MD, PhD, The Psychiatry Institute (MC 912) Department of Psychiatry, University of Illinois at Chicago 1601 West Taylor Street Chicago, Illinois, 60612 alexfeuillet@gmail.com Abstract. In this paper, we present PLACE, a comprehensive framework for studying node-level community structure. Instead of the well-known Q modularity metric, PLACE utilizes a novel metric, Ψ PL , which measures the difference between inter-community versus intra-community path lengths. We compared community structures in human healthy brain networks generated using these two metrics, and argued that Ψ PL may have theoretical advantages. PLACE consists of the following: 1) extracting community structure using top-down hierarchical binary trees, where a branch at each bifurcation denotes a collection of nodes that form a community at that level, 2) constructing and assessing mean group community structure, and 3) detecting node-level changes in community between groups. We applied PLACE and investigated the structural brain networks obtained from a sample of 25 euthymic bipolar I subjects versus 25 gender and age matched healthy controls. Results showed community structural differences in posterior default mode network (DMN) regions, with the bipolar group exhibiting left-right decoupling. Keywords: connectome, community structure, bipolar disorder, hierarchical trees Short Title: Community abnormalities in bipolar disorder