Experiment on Twins Finds Pre-Teen Years Key in Preventing Drug Abuse

Researchers have known for some time that people who display impulsive behaviors and focus on short-term rewards have significantly higher chances of becoming substance abusers than those who control their short-term impulses and focus on long-term rewards. Teenagers exhibit this tendency just as much as adults, if not more so. Current evidence indicates that both genetics and environmental factors play significant roles in influencing teens’ level of impulsivity.

Experiment on Twins

In 2011, researchers from the Washington University School of Medicine reported the results of a two-phase experiment designed to gather information about impulsive behaviors among teenagers. During the first phase of this experiment, more than 700 12-year-olds were asked to choose from one of two rewards for cooperating with the researchers. The first reward was an immediate payment of $7, while the second reward was a delayed payment of $10, to be delivered one week later. Thirty-five percent of the participants chose to receive the immediate payment, while 65 percent chose the delayed payment. Based on the findings of previous experiments by other researchers, the Washington University researchers preliminarily concluded that the children who took the immediate payment were more impulsive or short-term oriented than the children who took the delayed payment. Two years after the first phase of their experiment, the Washington University researchers re-contacted the children from the original study and asked them to come in for further testing; 82 percent of the children agreed to participate. Once the children were assembled, the researchers offered them the same choice of monetary reward for their cooperation. This time, only 28 percent of the children took an immediate payment of $7 over a delayed payment of $10.

Important Findings

After gathering the findings from the second phase of their experiment, the Washington University researchers came to several important conclusions. First, while the percentage of presumably impulsive children dropped between the ages of 12 and 14, most of the children who accepted the short-term reward of $7 at the age of 12 also accepted the same short-term reward at the age of 14. In addition, when compared to the children who chose the delayed reward, the children who chose the immediate reward scored higher on other tests that measure impulsivity, and also scored higher on tests that measure an individual’s willingness to seek out new, novel experiences. When compared to their relatively patient peers, this same group of relatively impulsive children also exhibited higher levels of behavioral problems and had a greater number of symptoms of conduct disorder, a childhood mental disorder centered on displays of defiance and criminal tendencies. Critically, the 14-year-old children who favored short-term rewards had a much higher level of involvement in substance abuse than the children who favored long-term rewards. While only 2 percent of the relatively patient children had experimented with marijuana, three times as many of the relatively impulsive children had done so. Additionally, while only 3.5 percent of the relatively patient children had started smoking, 9 percent of the relatively impulsive children were smoking.

The Role of Genetics

All of the children involved in the Washington University School of Medicine study were paired sets of identical and fraternal twins. This gave the researchers the opportunity to draw conclusions about the role of genetics in influencing teen impulsivity and the tendency toward behavioral problems and substance abuse. At both age 12 and age 14, the identical twins (who by definition have more genetic similarities than the paternal twins) made the same choices significantly more frequently than the paternal twins. From a statistical analysis of the responses of the different types of twins, the researchers concluded that genetics account for roughly 30 percent of a child’s impulsivity level at age 12 and roughly 51 percent of a child’s impulsivity level at age 14.

The Role of a Child’s Environment

According to the estimates made by the researchers from Washington University, 70 percent of a pre-teen’s level of impulsivity comes from non-genetic environmental factors such as income level, family stability, toxin exposure, educational level and degree of exposure to physically or sexually abusive situations. By age 14, however, slightly more than half of a child’s impulsivity level comes from genetic tendencies. Therefore, if public health officials and substance abuse specialists hope to intervene effectively in the lives of teenagers, they stand a better chance of success if they devise programs that reach children before their teen years begin.

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