One approach to disentangling these complex interactions is to use stepping stones such as brain structure to help bridge the gap between genetic and environmental risk factors and behavior (Figure 1). Genes do not code for behaviors, but for the building blocks of the cells whose interactions eventually give rise to those behaviors; conversely, the translation of environmental input into persistent behavioral changes occurs through alterations in brain systems and even structures. The advent of brain imaging revolutionized the neuroscience of behavior by making it possible to noninvasively study the brain in vivo. As an example, cortical thickness can be measured at a level of resolution high enough to detect differences in regions across the cortex that are also known to be functionally and cytoarchitecturally heterogeneous. The association of a particular behavioral feature with thickness in a specific cortical area may be a clue that the mechanisms involved in the development of that cortical region are also relevant to that behavior. In addition, finding that specific genetic polymorphisms affect a cortical region directs us to the functions of associated gene products.
