All participants were part of a longitudinal study that allowed determination of quantitative estimates of cigarette and alcohol use. Exposure to cigarettes and alcohol up to the time of the scan was calculated based on the longitudinally acquired data. Because alcohol and cigarettes were the most commonly used substances, values for lifetime use of alcohol and cigarettes and whether the individual met criteria for a substance use disorder before the scan were used as covariates in both VBM and SPSS analyses.
