Research ReportPreliminary Evidence of White Matter Abnormality in the Uncinate Fasciculus in Generalized Social Anxiety Disorder
Section snippets
Subjects
Sixty subjects (30 with GSAD and 30 age-, sex-, education-matched healthy control subjects [HC]) participated in this study. Demographic and clinical characteristics of the subjects are presented in Table 1. GSAD diagnosis was established using the Structured Clinical Interview for DSM-IV (SCID) with additional probes from the Social Phobia Interview (13) conducted by trained, master's-level clinical assessors, and the self-administered Liebowitz Social Anxiety Scale (LSAS) (14). None of the
MRI Protocol
Subjects were scanned with Turboprop DTI (12, 15) on a 3-T GE MRI scanner (General Electric, Waukesha, Wisconsin) using the following parameters: repetition time (TR) = 5000 msec, echo time (TE) = 94 msec, 8 spin-echoes per TR/blade, 5 k-space lines acquired per spin-echo (40 lines per blade), 128 samples per line, 16 k-space blades per image, field-of-view = 24 cm × 24 cm, 36 contiguous axial slices, slice thickness = 3 mm, 256 × 256 final image matrix. Diffusion-weighted images with b = 900
DTI Image Processing and Analysis
Details for image processing and analysis have been described elsewhere (16). In brief, the diffusion tensor model was fit to each voxel to create FA images for each subject. The Brain Extraction Tool of the software package FSL (Oxford Centre for functional MRI of the Brain, Oxford, United Kingdom) was applied on all b = 0 sec/mm2 volumes to remove the skull and noise outside of the brain. The resulting binary brain masks were then applied on the FA maps. The FA images from all subjects were
Results
Relative to HCs, subjects with GSAD exhibited significantly lower FA nearby the OFC localized (by Talairach coordinates, x = right, y = anterior, z = superior) to right uncinate fasciculus (UF; 18, 18, −15; 383 voxels; t = 2.88, p = .003, uncorrected; Figure 1A). No other areas of reduced WM FA were identified in the GSAD group. Extracted FA values (mean ± SD) from the UF cluster are shown in Figure 1B to show individual variability (HC: .32 ± .02 vs. GSAD: .31 ± .02; t58 = 2.41, p = .02,
Discussion
In this Turboprop DTI study, as predicted, we observed lower prefrontal fractional anisotropy localized to right UF WM in the area adjacent to the orbitofrontal cortex in individuals with GSAD compared with matched HC subjects. Anatomically, the UF is the major WM fiber tract that connects the inferofrontal and anterotemporal cortices, and it travels over the lateral nuclei of the amygdala, terminating in the OFC (Brodmann area 11–12) and subcallosal area (Brodmann area 25) (9). Thus, lower FA
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