Based on findings of reduced neurocognitive functioning in marijuana and alcohol using adolescents (Brown et al., 2000; Medina et al., 2007; Tapert & Brown, 1999, 2000; Tapert et al., 2002), we predicted that regions of decreased anisotropic diffusion would be associated with poorer performance on neuropsychological measures. Considering that increased FA in users may be associated with compensatory mechanisms, we hypothesized that FA in these brain areas would be associated with improved performance. In marijuana and alcohol using adolescents, scores on verbal learning and memory were expected to correlate positively with temporal FA, speeded processing and visuomotor sequencing with bilateral crus cerebri FA, and complex sequencing with FA in frontal regions and frontal association tracts such as the SLF.
