Increases in FA values and decreases in MD values are both associated with greater myelination and organization of neuronal fibre tracts (Le Bihan et al., 2001). Decreased MD is generally interpreted as “better” WM integrity, whereas decreased FA is believed to represent “worse” WM integrity (Bava et al., 2009). One study reviewed here reported higher FA for AU youth (Cardenas et al., 2013), potentially reflecting the very high rates of alcohol use within this sample (M = 60 drinks/month). However, the majority of the studies found AU youth to have poorer measures of WM integrity (lower FA values) than non-AU youth across a number of areas (corona radiata, inferior/superior longitudinal fasciculus, inferior fronto-occipital fasciculus, corpus callosum, internal and external capsules, and commissural, limbic, brainstem, and cortical projection fibres; Jacobus et al., 2009; McQueeny et al., 2009; Thayer et al., 2013). Overall, group differences in MD were not found between AU and non-AU youth (Cardenas et al., 2013; Jacobus et al., 2009; Luciana et al., 2013; Thayer et al., 2013). This pattern was also reported in the single longitudinal study reviewed,
