This study identified genetically-associated circuitry via resting-state coupling in order to examine genomic relations with stable functional networks. Thus, an important next step in this line of research will be to investigate the functional and structural features of externalizing PS-related brain networks. First, examining how connectivity in this network shifts in response to cognitive/emotional challenges, like inhibitory control tasks, will be important to address in future research. Connectivity between PFC executive-control regions (rACC, IFG) and subcortical regions crucial for emotion/salience (amygdala) increases with the demand for inhibitory control (Spielberg et al., 2015). Based on limited research on functional connectivity and impulsivity (Farr et al., 2012; Shannon et al., 2011) we would not expect high externalizing individuals to show this increase in PFC-subcortical connectivity with increasing inhibitory control demands in functional tasks. An alternative hypothesis, based on the present findings, is that bottom-up (e.g., affective) processes would influence inhibitory control to a greater extent in high externalizing individuals, rather than top-down control simply being deficient. Second, it will be important to isolate the anatomical pathways that enable the identified functional network, given that resting-state fMRI coupling does not imply direct anatomic connection and these analyses are not bounded by such connections.
