MRI-based morphometric topographic parcellation of human neocortex in trichotillomania

The purpose of the present study was to test specific hypotheses regarding volumetric changes of the neocortex between 10 female trichotillomania (TTM) subjects and 10 female normal controls. A standard three-dimensional (3-D) brain coordinate system was imposed over each newly acquired native magnetic resonance imaging (MRI) scan for positional normalization and 3-D shape/geometric localization analyses were based on the midpoints of anterior and posterior commissures, and the longitudinal fissure. The brain segmentation method, using well-characterized semiautomated intensity and differential contour algorithms by signal intensity-frequency histograms, was used blind to segment the principal gray and white matter structures. The segmented neocortical ribbon was subdivided into 48 regions (i.e. parcellation units) per hemisphere via a new method of morphometric topographic parcellation. There were no significant volumetric changes of the precentral gyrus, postcentral gyrus, supplementary motor cortex or opercular cortex in TTM patients compared with control subjects. A broader analysis as a hypothesis-generating post-hoc effort showed that TTM subjects exhibited significantly reduced left inferior frontal gyrus volume of 27% (t = 2.21, d.f. = 18, P = 0.04) and enlarged right cuneal cortex volume of 40% (t = -2.30, d.f. = 18, P = 0.03) compared to normal controls. This is the first report of a structural neocortex abnormality in TTM. Results are discussed in terms of the behavioral specialization of these two brain neocortical regions and the complex interractions between visual and sensorimotor cortices. The results also showed the feasibility of the MRI-based morphometric topographic parcellation for investigation of the human neocortex in neuroscience research.