Given the above results, we focused on the left amygdala and right VS for the sibling analyses. Contrast 3 significantly predicted left amygdala volumes (β=12.56, t(302.80)=2.97, p=0.003), supporting the predispositional hypothesis. We did not find evidence for either the causal (Contrast 1) or graded liability (Contrast 2) hypotheses. Concordant unexposed pairs had larger amygdala volumes than all other groups, even unexposed members of discordant pairs (Figure 2). Despite not using cannabis, these unexposed individuals from discordant pairs had amygdala volumes resembling cannabis-exposed individuals, including their exposed siblings. None of the three contrasts significantly predicted right VS volumes (fixed effects predicting all volumes are presented in eTable 11).
