Details regarding BOLD fMRI acquisition and analysis may be found in the Supplement. Briefly, amygdala habituation to threat-related stimuli, our outcome variable of interest in this analysis, was calculated as the linear decrease in reactivity over successive face-matching blocks (i.e., block 1 > block 2 > block 3 > block 4). BOLD paramete estimates from clusters within the left and right basolateral amygdala ROIs exhibiting a main effect for the habituation contrast were extracted using the VOI tool in SPM8 (http://www.fil.ion.ucl.ac.uk/spm) and exported for regression analyses. Extracting parameter estimates from clusters activated by our fMRI paradigm, rather than those specifically correlated with our independent variables of interest, precludes the possibility of any correlation coefficient inflation that may result when an explanatory covariate is used to select a region of interest. We have successfully used this strategy in prior studies (Bogdan, Williamson, & Hariri, 2012). The distribution of this outcome measure across genotype and ELS groups is reported in the Supplement (Table S4).
