On the one hand it is unsurprising that the brain
On the one hand, it is unsurprising that the domoic acid has not been investigated as a source of susceptibility. First, research guided by neurobiological susceptibility models tends to group individuals by susceptibility markers, categorize environments as high vs. low on a valenced dimension (or as high on oppositely valenced dimensions), and examine their interactive effects on a developmental outcome. It might then be determined whether the association between the moderator and outcome is significant at both ends of the environmental variable (Roisman et al., 2012). Concrete, reliable indices of an individual\'s group membership are readily derived when the susceptibility factor is, for example, genotype or temperament. However, neuroimaging researchers do not typically (but we argue increasingly could) characterize individuals in their samples according to high/low standing on a parameter of brain function, structure, or related properties, and/or examine the interactive effects of brain and social-contextual factors on developmental outcomes (Fig. 2). Second, in developmental cognitive neuroscience work, the statistical approaches commonly used in functional neuroimaging analyses identify group-based trends. In fMRI analyses, contrasts between task events within the same group of individuals or between groups of individuals who differ in social context (e.g., maltreated vs. non-maltreated) or developmental outcome (e.g., depressed vs. non-depressed) are typically assessed rather than intragroup variability characterized, which is necessary to examine individual differences. Likewise, researchers rarely use quantified properties of the brain that draw on findings from group-based analyses to guide new work that uses them as markers to index individuals’ susceptibility to social influences. Although these steps can be taken, this renders much extant neuroimaging research lacking with regard to brain structure/function indices as markers of susceptibility. Finally, neuroimaging data are expensive and time-consuming to collect and analyze. These attributes can limit their integration within the longitudinal research designs needed to track developmental outcomes. On the other hand, it is surprising that the brain has not been investigated as a source of susceptibility. For one, the brain is the primary determinant of behavior. Although changes in behavior are influenced by both congenitally and socially determined factors that create a backdrop for the brain\'s influence, both must operate through brain circuits to affect behavior. According to the neurosensitivity hypothesis (Pluess and Belsky, 2013), sensitivity of the central nervous system, which is jointly determined by direct and interactive effects of genetic and environmental factors, is the primary mechanism underlying susceptibility. Likewise, in considering that subjective experience of social contexts is central to transmitting their influence, it cannot be ignored that “[a]ll operations of the mind, conscious and unconscious (and that includes the perception and conceptualization of experiences), have to be based on the working of the brain” (Rutter, 2012, p. 17149). Indeed, while the brain\'s influence on behavior is instrumental for considering its role in shaping developmental outcomes, brain indices may be particularly useful for capturing differences in what Pluess (2015) terms sensitivity, the extent to which input coming from external influences is generated, perceived, and internally processed. Sensitivity represents the first, requisite leg of susceptibility and does not necessarily have a one-to-one correspondence with responsivity, or the behavioral output that captures the extent to which one responds to the environment. To this end, focusing on the neural components of behavior is beneficial because assessing the brain allows sensitivity (and possibly the responsivity that follows) to be parsed into elements associated with different functions (e.g., affective reactivity, reward processing, conflict monitoring) that may not be evident through self-reported or observed behavior. A related advantage of using brain indices over other established susceptibility factors in testing hypotheses about adolescent neurobiological susceptibility to social context is the ability to reveal possible contributions from different classes of emotion, cognition, and motivation.