title: Discovering brain regions relevant to obsessive-compulsive disorder identification through bagging and transduction.
abstract: In the present study we applied a multivariate feature selection method based on the analysis of the sign consistency of voxel weights across bagged linear Support Vector Machines (SVMs) with the aim of detecting brain regions relevant for the discrimination of subjects with obsessive-compulsive disorder (OCD, n=86) from healthy controls (n=86). Each participant underwent a structural magnetic resonance imaging (sMRI) examination that was pre-processed in Statistical Parametric Mapping (SPM8) using the standard pipeline of voxel-based morphometry (VBM) studies. Subsequently, we applied our multivariate feature selection algorithm, which also included an L2 norm regularization to account for the clustering nature of MRI data, and a transduction-based refinement to further control overfitting. Our approach proved to be superior to two state-of-the-art feature selection methods (i.e., mass-univariate t-Test selection and recursive feature elimination), since, following the application of transductive refinement, we obtained a lower test error rate of the final classifier. Importantly, the regions identified by our method have been previously reported to be altered in OCD patients in studies using traditional brain morphometry methods. By contrast, the discrimination patterns obtained with the t-Test and the recursive feature elimination approaches extended across fewer brain regions and included fewer voxels per cluster. These findings suggest that the feature selection method presented here provides a more comprehensive characterization of the disorder, thus yielding not only a superior identification of OCD patients on the basis of their brain anatomy, but also a discrimination map that incorporates most of the alterations previously described to be associated with the disorder.
authors.affiliation: Dept.Signal Processsing and Communications, Universidad Carlos III de Madrid, Madrid, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Parrado-Hernández
authors.affiliation: Dept.Signal Processsing and Communications, Universidad Carlos III de Madrid, Madrid, Spain.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Gómez-Verdejo
authors.affiliation: Department of Electrical and Computer Engineering, The University of New Mexico, 1 University of New Mexico, Albuquerque, NM 87131-0001, USA. Electronic address: manel@unm.edu.
authors.forename: Manel
authors.initials: M
authors.lastname: Martínez-Ramón
authors.affiliation: Dept.Computer Science and CSML, University College London, London WC1E 6BT, UK.
authors.forename: John
authors.initials: J
authors.lastname: Shawe-Taylor
authors.affiliation: Bellvitge Biomedical Research Institute-IDIBELL, Psychiatry Service, Bellvitge University Hospital, Barcelona, Spain; Carlos III Health Institute, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Spain; Dept.of Clinical Sciences, School of Medicine, University of Barcelona, Barcelona, Spain.
authors.forename: Pino
authors.initials: P
authors.lastname: Alonso
authors.affiliation: CRC Hospital del Mar, Barcelona, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Pujol
authors.affiliation: Bellvitge Biomedical Research Institute-IDIBELL, Psychiatry Service, Bellvitge University Hospital, Barcelona, Spain; Carlos III Health Institute, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Spain; Dept.of Clinical Sciences, School of Medicine, University of Barcelona, Barcelona, Spain.
authors.forename: José M
authors.initials: JM
authors.lastname: Menchón
authors.affiliation: Bellvitge Biomedical Research Institute-IDIBELL, Psychiatry Service, Bellvitge University Hospital, Barcelona, Spain; Carlos III Health Institute, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Spain; Dept.of Clinical Sciences, School of Medicine, University of Barcelona, Barcelona, Spain.
authors.forename: Narcis
authors.initials: N
authors.lastname: Cardoner
authors.affiliation: Bellvitge Biomedical Research Institute-IDIBELL, Psychiatry Service, Bellvitge University Hospital, Barcelona, Spain; Carlos III Health Institute, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Spain.
authors.forename: Carles
authors.initials: C
authors.lastname: Soriano-Mas
mesh_terms: D000328:Adult; D000465:Algorithms; D001185:Artificial Intelligence; D001921:Brain / Q000473:pathology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009415:Nerve Net / Q000473:pathology*; D009771:Obsessive-Compulsive Disorder / Q000473:pathology*; D010363:Pattern Recognition, Automated / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: MRI; Machine learning; Obsessive–compulsive disorder; Transduction; Voxel selection