title: A reversal coarse-grained analysis with application to an altered functional circuit in depression.
abstract: BACKGROUND
  When studying brain function using functional magnetic resonance imaging (fMRI) data containing tens of thousands of voxels, a coarse-grained approach - dividing the whole brain into regions of interest - is applied frequently to investigate the organization of the functional network on a relatively coarse scale. However, a coarse-grained scheme may average out the fine details over small spatial scales, thus rendering it difficult to identify the exact locations of functional abnormalities.
  
  
  METHODS
  A novel and general approach to reverse the coarse-grained approach by locating the exact sources of the functional abnormalities is proposed.
  
  
  RESULTS
  Thirty-nine patients with major depressive disorder (MDD) and 37 matched healthy controls are studied. A circuit comprising the left superior frontal gyrus (SFGdor), right insula (INS), and right putamen (PUT) exhibit the greatest changes between the patients with MDD and controls. A reversal coarse-grained analysis is applied to this circuit to determine the exact location of functional abnormalities.
  
  
  CONCLUSIONS
  The voxel-wise time series extracted from the reversal coarse-grained analysis (source) had several advantages over the original coarse-grained approach: (1) presence of a larger and detectable amplitude of fluctuations, which indicates that neuronal activities in the source are more synchronized; (2) identification of more significant differences between patients and controls in terms of the functional connectivity associated with the sources; and (3) marked improvement in performing discrimination tasks. A software package for pattern classification between controls and patients is available in Supporting Information.
authors.affiliation: College of Mathematics and Computer Science, Key Laboratory of High Performance Computing and Stochastic Information Processing (Ministry of Education of China), Hunan Normal University Changsha, Hunan, China.
authors.forename: Shuixia
authors.initials: S
authors.lastname: Guo
authors.affiliation: College of Mathematics and Computer Science, Key Laboratory of High Performance Computing and Stochastic Information Processing (Ministry of Education of China), Hunan Normal University Changsha, Hunan, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Centre for Computational Systems Biology, School of Mathematical Sciences, Fudan University Shanghai, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Centre for Computational Systems Biology, School of Mathematical Sciences, Fudan University Shanghai, China ; Department of Computer Science, University of Warwick Coventry, U.K.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Feng
keywords: Reversal coarse-grained analysis; source location; voxel-wise time series