One of the overarching themes of psychological research is the interplay between genetics and the environment (i.e., nature-nurture). In the past decade or so we have made considerable advances in understanding genetic contributions to human traits/behavior, but there is still a long ways to go.
Of interest to those of us studying reward processing, discounting, etc… are genes encoding for dopamine receptors. Sweitzer et al. (2013) review some of this research in the introduction of their study investigating the dopamine D4 receptor and discounting among childhood socioeconomic status. Broadly (and to summarize), the DRD4 protein (dopamine D4 receptor) is expressed in the prefrontal cortex and subcortical regions (e.g., striatum) linked to reward processing. One particular allele of the DRD4 gene (7-repeat allele) relates to self-regulation, addictive behaviors, gambling, risk taking, and more generally, novelty seeking. Recent work complicated this early behavior-gene finding, prompting more comprehensive work that indicated a more nuanced relationship where early life stress might modify gene expression. Specifically, research suggests this relationship between the DRD4 7-repeat allele and novelty seeking only manifests IF the individual experienced early life stress. Sweitzer et al. (2013) explain this using the framework of the diathesis stress model where genetic vulnerabilities (i.e., the diathesis) do not manifest unless coupled with a stress. In fact, they summarize research that shows the DRD4 7-repeat allele is associated with positive outcomes in favorable environments, suggesting a differential susceptibility.
In this study, Sweitzer et al. (2013) examined the relationship between the DRD4 length and temporal discounting AND tested whether this relationship was modified by childhood socioeconomic status. A sample of ~546 participants between 30-54 years underwent genotyping, completed a temporal discounting task, and completed the two-factor Hollingshead Index of childhood socioeconomic status (based on parental education and occupational grade) and current socioeconomic status. This study used a correlational design with genotype (presence vs. absence of DRD4 7-repeat allele) and SES as the main predictors (i.e., quasi-IV) and discounting as the main outcome variable (i.e., DV).
Sweitzer et al. (2013) started by examining correlations between socioeconomic status and discounting. They found that individuals from lower socioeconomic status discounted the future more steeply. Then, they tested for an interaction between genotype and childhood SES on temporal discounting. They did in fact find an interaction. Lower childhood SES (but not adulthood SES) correlated with steeper delay discounting among individuals with the DRD4 7-repeat allele. The authors tested for several alternative hypotheses and did not find evidence that this relationship could be explained by age, IQ, gender, or adulthood SES. Moreover, individuals with the DRD4 7-repeat allele who grew up with higher SES actually discounted the future the least.
This differential effects depending on childhood SES (i.e., lower versus higher) suggests that this allele plays a role in susceptibility to environmental cues.
This research provides critical background on the modifying effect that childhood environment plays in decision-making. Moreover, it links this modifying effect to behavioral genetics. Future work in my lab will likely investigate whether childhood adversity modifies the relationship between spontaneous eyeblink rate and discounting (and risk aversion). Obviously I do not have the means to genotype anyone, but I think it would be pretty cool to expose undergraduate students at a small public university to methods that indirectly measure similar biomarkers.
As a side note, the authors used the word “salubrious” in the abstract, which I learned means “conducive or favorable to health or well-being.”
Sweitzer, M. M., Halder, I., Flory, J. D., Craig, A. E., Gianaros, P. J., Ferrell, R. E., & Manuck, S. B. (2013). Polymorphic variation in the dopamine D4 receptor predicts delay discounting as a function of childhood socioeconomic status: Evidence for differential susceptibility. Social, Cognitive, and Affective Neuroscience, 8, 499-508. doi:10.1093/scan/nss020