DTI analysis identified 9 WM regions including frontal white matter, external capsule, superior longitudinal fasciculus, splenium of corpus callosum, anterior corona radiate, and occipital white matter of the left hemisphere and right superior corona radiata where AUD participants had lower FA compared to controls (Table 2, Figure 5), suggesting lower WM integrity confirming previous findings (Bagga et al., 2014, Fortier et al., 2014, Monnig et al., 2013, Pfefferbaum et al., 2010b). The callosal body was also found to be affected (unadjusted p<0.008) as commonly reported (e.g., Pitel et al., 2010) but did not survive a CMT. These FA differences were further explained by the contribution of higher RD in 6 WM regions and lower AD in left external capsule (WM03). Proton diffusion in tissue is highly sensitive to differences in the microstructural architecture of cellular membranes. Larger average spacing between membrane layers will result in higher diffusivity, whereas smaller spaces will lead to lower diffusivities (Alexander et al., 2007). Research has demonstrated that the parallel organization of WM fiber bundles and axonal membranes is the primary determinant of diffusion anisotropy
