RESUMO
Multidimensional scaling (MDS) is a multivariate statistical technique that can be used to define subsystems of functionally connected brain regions based on the analysis of functional magnetic resonance imaging (fMRI) data. Here we introduce three-way multidimensional scaling as a method for the analysis of a group of fMRI data, which yields both a generic interregional configuration in low-dimensional space and a measure of each individual's deviation from the generic configuration. The distance between two generic interregional configurations obtained by MDS of two groups of data can be minimized by generalized Procrustes analysis, and the probability under the null hypothesis (that the two groups are sampled from the same population) of any residual group difference in interregional configurations can be assessed by a permutation test. These methods are developed and applied to activated fMRI time series acquired from 19 patients with schizophrenia and 20 normal comparison subjects during the performance of a semantic categorization and subvocal rehearsal task. The first three scaling dimensions are interpretable in terms of the major anatomical or functional subsystems of the activated system: "left-right," "input processing-other," and "subvocal output-other". We found no significant global or local differences between groups in interregional configurations in this 3D space. However, there was significantly greater variability of interregional configurations within the group of patients with schizophrenia. The implications for schizophrenia as a disconnexion disorder are discussed.
