Putting a very high premium on receiving a reward now rather than later has been linked to drug abuse and behavioral disorders in several studies. Now, Dr. Andrey P. Anokhin and colleagues at the Washington University School of Medicine have provided the first estimate of the relative contributions of genetic and environmental factors to a young teen’s response to a now-versus-later reward option. Although genetics significantly influenced the children’s choices, environmental factors also contributed, suggesting that behavioral and other interventions may be able to promote forward-looking decision-making and reduce the risks related to impulsivity.
The researchers recruited 372 pairs of 12-year-old twins and told each child that, as a reward for cooperating with a battery of assessments, he or she could either have $7 right away or wait and receive $10 in the mail in a week. Two years later, when the twins were 14, the researchers were able to contact 82 percent of them and repeat the same assessments and reward alternatives.
Consistent with previous research, the children who chose the immediate reward appeared to be headed for more behavioral problems than their more patient peers. They scored higher on the novelty-seeking and lower on the self-directedness scales of the Temperament and Character Inventory, scored higher on an assessment of impulsivity, and reported more symptoms of conduct disorder.
Although few of the participants had used drugs by age 14, those who chose the immediate reward were significantly more likely to report having done so during the past year. For example, more than 6 percent of them had tried marijuana by age 14, whereas only 2 percent of those who selected a delayed reward had done so; the rates for cigarette smoking were 9 percent and 3.5 percent, respectively. Immediate reward choosers were also three times as likely as their more patient counterparts to have been suspended from school in the past year.
The percentage of children who took the $7—that is, discounted the reward by 30 percent to avoid a 7-day delay in receiving it—declined as the children grew, from 35 percent at age 12 to 28 percent at age 14. However, most of the children who opted for the $7 payment at age 14 had also done so at age 12, suggesting that the disposition to discount heavily is stable over this span of development.
|Higher levels of past-year use of tobacco, alcohol, and marijuana||Lower-income families, as indicated by parent occupation|
|More symptoms of conduct disorder|
|Higher rates of novelty-seeking and impulsivity|
|Lower rates of being self-directed|
Genes and Intervention
To shed light on the discounting of delayed rewards as a potential target for intervention, the researchers calculated the percentages of the children’s choices attributable to their genetic makeup and environmental influences. At both ages, identical twin pairs chose the same option much more often than fraternal twin pairs did. The researchers estimated that the children’s genes accounted for 30 percent of their choices at age 12 and 51 percent at age 14.
Although the genetic component of decisionmaking is largely fixed, interventions that address environmental factors can improve valuation of future rewards. Dr. Anokhin says, “Environment can modify decisionmaking style, particularly among youth. It’s important to teach kids the skills for making good decisions and controlling immediate impulses—weighing options and thinking about long-term consequences. Research on ways to do that would be of great value.”
The new findings suggest that the relative role of genetic factors in shaping individual differences in choice behavior tends to increase as adolescents approach the age when substance use typically begins. This underscores the importance of early assessment and intervention for those at increased risk.
“Our results highlight the importance of individual differences in decision styles as a potential predictor of adolescent problems that tend to cluster together, including substance abuse and symptoms of conduct disorder,” says Dr. Anokhin. “A viable hypothesis is that they are all problems of response inhibition—being unable to withstand the temptation and so choosing the immediate opportunity despite understanding the benefits of waiting.”
Dr. Harold Gordon of NIDA’s Division of Clinical Neuroscience and Behavioral Research says, “Studies such as Dr. Anokhin’s serve to chip away at the underlying biological and behavioral correlates to substance abuse which, when they are better understood, may give us new targets for therapeutic strategies.”
Anokhin, A.P., et al. Heritability of delay discounting in adolescence: A longitudinal twin study. Behavior Genetics 41(2):175–183, 2011. [Full Text (PDF, 238KB)]