Subgrouping of MDD cohort based on individual FA values.
This figure shows the subgrouping of the MDD cohort based on individual FA values, and double dissociation of VTA/SN and MFB abnormalities across these two subgroups. (A) Scatterplots of FA values from the VTA/SN cluster from MDD subjects (blue) and control subjects (pink). There was a statistically significant gap in the middle of the VTA/SN values for MDD subjects; the values above this gap were all outside the range of control values. When contrasts were calculated separately for MDD subjects in the abnormal VTA/SN (10 MDD and 10 controls) versus the normal VTA/SN (12 MDD and 12 controls) MDD subgroups, (B) abnormal VTA/SN MDD subjects exhibited significantly elevated FA bilaterally in the ventral tegmental area/substantia nigra (VTA/SN), localized to both the SN and the VTA and a trend toward significance in this region in the left hemisphere, while (C) MDD subjects in the normal VTA/SN subgroup did not exhibit any significant FA differences in this region. In contrast, (B) abnormal VTA/SN MDD subjects did not exhibit any significant FA differences overlying the medial forebrain bundle/lateral nucleus of the hypothalamus (MFB/LNH), while (C) normal VTA/SN MDD subjects exhibited a trend toward significant reduction in FA values in this region. Translucent green in images on left indicates a priori AOEs for the (B) VTA/SN and (C) MFB/LNH in the slices shown, which were used to constrain the initial contrast analysis. The color bar indicates the range of p values in this figure, from the threshold (p<0.05) to the order of magnitude of the voxel of peak significance (i.e. smallest p value) in the VTA/SN for elevated FA and from the threshold (p<0.05) to the order of magnitude of the voxel of peak significance in the MFB for reduced FA, color in images is viewed using trilinear interpolation. Warm tones (red, orange, yellow) indicate regions in which MDD subjects exhibited elevated FA relative to control subjects; cool tones (blues) indicate regions in which MDD subjects exhibited reduced FA relative to control subjects. RH: right hemisphere; LH: left hemisphere.