In this review article, I propose a framework for understanding the neurobiological processes that guide how individuals navigate and internalize environments. Previous work brought to attention the empirical evidence that some individuals with particular temperaments, physiological characteristics and, more recently, genetic polymorphisms, demonstrate heightened effects of social environments on development (Belsky & Pluess, 2009). My review article, published in Psychological Bulletin, steps beyond this question of whether individuals vary in responses to social environments, which is now well-established, to why individuals differ in their responses. In other words, I set out to address: What underlies this variation in sensitivity to experience, and how does it develop?
Since the publication of seminal work on gene-environment interactions (Caspi et al., 2002, 2003), gene-environment interaction has become quite common in investigations of individual differences in responsiveness to environmental factors. Collectively, the work suggests that particular genes encoding neurochemicals relate to the degree that social contexts have enduring consequences on developmental outcomes. What was missing in this area was an explanation as to how variation of these neurobiological systems shapes individual differences in the enduring consequences of environmental factors. The first part of my review article thus addresses the neurobiological functions of genes commonly implicated in gene-environment interaction studies of sensitivity. These functions bridge genetic variation affecting neural systems to actual differences in neuroplasticity processes to environmental inputs, explaining mechanistically why particular genotypes might be linked to larger effects of the environment on development.
Inherent to the notion of plasticity is the critical role of experience. Plasticity means that environments are interacting with biology in the development of traits. Despite this accepted view of development as plastic, and thus involving an ongoing interplay of biology and experience, there still exists a heavy emphasis on genetics, in and of itself, wherever one or more genes might be implicated. In the second part of my review, a developmental framework is proposed that accounts for the dynamic nature of the biological processes that are affected by genes. Simply put, if a genetic factor shapes plasticity to the environment, then the history of environmental effects on the biology of the brain is as important to understanding outcomes as the genetic susceptibility factor: Any long-term consequences of such a factor is intrinsically dependent on the surrounding environmental context.
Taken together, the importance of this article lies in its novel insights into the mechanisms that may account for individual variations in sensitivity at a point where the field is in need of such an analysis. For the increasing number of developmentalists turning to research on genetic and biological markers of sensitivity, this article serves to inform the biological role of the prominently studied genes in human development. It also highlights other biological systems relevant to how experiences are registered and internalized. The article advances the current literature's myopic focus on identifying genetic plasticity markers to understanding the plasticity processes at play. The plasticity of neurobiological systems directly accounts for who responds and adapts and to what in the environment. This is essential for understanding developmental change, and for identifying targetable mechanisms of risk. After all, changing genes is not an option.
Ultimately, this article is intended to jumpstart more in-depth research aimed at understanding the nuanced developmental trajectories of individuals with different susceptibilities and unique histories. Understanding how biological tendencies are modified by experience will pave the way for tailored interventions that target the specific needs of individuals and, ultimately, improve psychological and physical health outcomes. I will be continuing this work as a scholar at the Child and Family Research Institute at the University of British Columbia. In this next phase, I will investigate the epigenetic mediators bridging the interplay of genetic variation and experience to neurodevelopment.
Belsky, J., & Pluess, M. (2009). Beyond diathesis stress: Differential susceptibility to environmental influences. Psychological Bulletin, 135 (6), 885–908.
Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., et al. (2002). Role of genotype in the cycle of violence in maltreated children. Science, 297 (5582), 851–854.
Caspi, A., Sugden, K., Moffitt, T. E., Taylor, A., Craig, I. W., Harrington, H., et al. (2003). Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene. Science, 301 (5631), 386–389.