The shared genetic influences on addiction with these other brain based phenotypes and our implication of roles for variants in “cell adhesion” genes in many of these phenotypes underscore the likelihood that the biology of these systems will demand better and better approaches to understanding more of the details of the estimated ca. 1014 synaptic connections in the cerebral cortex, and those in other areas [299]. Gross phenotypes, such as lobar brain volumes, are likely to vastly underrepresent the true complexity of the qualitative differences that are driven by these gene variants, and provide only weak reporters for quantitative differences. The present genetic analyses underscore the urgency of developing better approaches to elucidating individual differences in connectivities in human brain, both living and postmortem.
