This study of a community sample of pre-adolescent youth identified early initiators of several risk behaviors described by a single factor, confirming the existence of a general risk-taking tendency at this early age. We also found evidence for a general tendency toward impulsive behavior defined by both sensation seeking and lack of thinking and planning when acting. Furthermore, consistent with our expectations concerning the importance of impulsivity as a precursor to early risk behavior, impulsivity was strongly related to risk behavior initiation. In addition, differences in externalizing and correlated internalizing problem behaviors were highly related to impulsivity, but these behaviors were not strongly related to risk taking once impulsivity was controlled. This finding suggests that impulsivity plays a large role in the emergence of both externalizing and health-risk behaviors. Both working memory performance and reversal learning (reward processing) were inversely related to impulsivity. However, none of the ECFs was directly related to risk behavior apart from relations with impulsivity, and as reflected in the small amount of variation explained in impulsivity, their relations with impulsivity were not strong. Performance on the cognitive control Stroop task was highly related to working memory performance; however, it was not related to either impulsivity or risk behaviors apart from working memory. Hence, the findings only support an indirect role for ECF in the emergence of early risk taking.
The central role of impulsive tendencies in the emergence of early risk behaviors is consistent with findings observed by others (Block et al., 1988
; Crawford et al., 2003
; Wong et al., 2006
). It is also consistent with the theorizing of Chambers et al. (2003)
and Spear (2000)
, who suggest that adolescence is the period when the rise in activity of the dopamine system encourages experimentation with novel and exciting behaviors. Our finding that age was positively related to impulsivity and that impulsivity mediated the relation between age and risk behavior is also consistent with this explanation.
The finding that impulsivity was highly related to externalizing behaviors was expected since such problems are characterized by deficits in impulse control (Gottfredson & Hirschi, 1990
; Waschbusch, 2002
; Waschbusch et al., 2002
). We were surprised however to find that externalizing behaviors did not correlate with risk behavior once impulsivity was controlled. Tarter’s neurobehavioral disinhibition model explicitly predicts such an association (Tarter et al., 2004
; Tarter et al., 2003
). Furthermore, longitudinal studies find that early evidence of conduct disorder and other externalizing behaviors is related to later drug use and fighting (Zucker, 2006
). However, impulsivity may be the central predisposing condition underlying both early manifestations of conduct disorder and later health-risk behavior. Studies that examine very early temperamental factors find that behaviors symptomatic of poor behavior control predict later externalizing problems (Caspi et al., 1995
; White et al., 1994
), suggesting that impulsivity is an important factor in the development of such outcomes. Our results support this conclusion, although a potential additional link between externalizing behavior and risk behavior cannot be ruled out given the presence of some, albeit statistically non-significant, relation that remains.
The finding that working memory capacity was indirectly related to risk behavior initiation by virtue of its relation with impulsivity has not to our knowledge been previously observed. This finding suggests that youth with greater ability to manipulate information in working memory have greater control over sensation seeking and other impulsive drives. The finding is also consistent with research linking working memory performance with proxies for risky decision making, such as the IGT (Bechara et al., 1998
; Bechara et al., 2001
; Fellows & Farah, 2003
). It is also consistent with interventions that find that improved working memory in children leads to reduced symptoms of impulsive behavior (Klingberg et al., 2005). The importance of working memory to the overall ability of PFC to exert control over behavior has often been noted (Fuster, 1997
; Miller & Cohen, 2001
) and is consistent with theories of PFC function that place particular emphasis on this ability. It is quite likely that youth who have limited ability to consider multiple and potentially conflicting goals are less likely to think before acting and to temper their interest in novel and exciting experiences. This would lead them to develop a relatively stable style of behavior that is observed in trait measures of impulsivity. Working memory capacity is also strongly related to general cognitive ability as assessed in intelligence tests (Colom, Abad, Quiroga, Shih, & Flores-Mendoza, 2008
; Shamosh et al., 2008
). It is possible therefore that working memory capacity is responsible for the small but persistent correlation that has been observed between IQ and youth engagement in multiple risk behaviors (Henry & Moffitt, 1997
; Lynam, Moffitt, & Stouthamer-Loeber, 1993
The finding that reversal learning performance (reward processing) was inversely related to impulsivity has also to our knowledge not been observed. This finding suggests that youth with deficits in the ability to adjust to new reinforcement contingencies are more likely to exhibit impulsive tendencies. The finding is consistent with studies of adults who suffered lesions to orbitofrontal brain regions and who also exhibit impulsive decision making (Fellows & Farah, 2003
; Rolls, Hornak, Wade, & McGrath, 1994
). Youth with such deficits may well develop impulsive styles of behavior that fail to recognize changes in reward contingencies. Furthermore, youth who exhibit weak performance on both working memory and reversal tasks would be expected to develop even greater impulsive behavior styles. Indeed, working memory and reversal learning performance were largely unrelated, consistent with the different brain regions to which they have been associated (dorsolateral for working memory and orbitofrontal for reversal learning).
Despite the directionality in our SEM, the relations between impulsivity and either working memory or reversal learning performance are purely correlational and subsequent waves of our study may help to determine whether development of ECF in general and working memory or reversal learning in particular predict declines in impulsivity. It is possible for example that impulsivity interferes with working memory performance by challenging the system with task irrelevant response tendencies that are difficult to control. This may lead to poorer performance on working memory tasks. It is also possible that impulsivity reduces attention to changes in reward contingencies. If either of these were the case, then developmental changes in impulsivity would predict changes in working memory or reversal learning rather than the other way around.
Another possibility regarding the relation between ECF and impulsivity is that as adolescents mature, their ability to control impulsivity increases and is more readily observable across different facets of ECF. Research on the development of ECF suggests that cognitive control ability is not fully mature until age 15 and that working memory and reward processing continues to mature into young adulthood (Huizinga et al., 2006
; Luciana, Conklin, Hooper, & Yarger, 2005
). Perhaps these functions, especially cognitive control, are not sufficiently developed until mid-adolescence to slow down the increase in impulsivity that characterizes adolescence. Our results indicate that age was positively related to working memory and to Stroop performance. Although these functions were not strong enough to inhibit age related increases in impulsivity, they may gain in strength as the PFC matures. This may explain why the research program by Nigg and colleagues finds a relation between impulse control and drug use at ages 15 to 17 but not at ages 12 to 15 (Nigg et al., 2006
The finding that measures of cognitive control (Stroop and flanker tasks) and reward processing (BART) were not related to impulsivity, risk behaviors, or externalizing symptoms was somewhat surprising given the central roles that they are assumed to play in these outcomes. It is important to keep in mind however that one measure of cognitive control (Stroop) was highly related to working memory and hence may not have contributed prediction beyond what it shared with that ability. Nevertheless, other research has also failed to find any relations between ECFs and early use of drugs (Nigg et al., 2004
; Tarter et al., 2003
), and research using proxies for risk taking such as the IGT also fail to find strong relations with ECFs in adolescents (Crone & van der Molen, 2004
; Hooper et al., 2004
). Results of the BART have to our knowledge only been correlated with drug use in small and older adolescent samples (Aklin et al., 2005
; Lejuez, Aklin, Zvolensky et al., 2003
Discrepancies between Adult and Early Adolescent Relationships
Given the absence of relations between several ECFs with early risk behaviors and the weak relation of working memory and reversal learning in comparison with impulsivity, it is important to ask why these measures of ECF correlate with drug use more strongly in adults (Bechara & Martin, 2004
) or youth with more serious substance use disorders (Tarter et al., 2003
). One possibility is that as youth experience increased drug use, ECFs become compromised so that their performance deteriorates. There is evidence that heavy use of potentially addictive drugs alters brain function producing deficits in working memory and inhibitory control (Jentsch & Taylor, 1999
). Over time, these effects could introduce correlations between ECFs and drug use. For example, the finding that ECF did not correlate with drug use at ages 12 to 15 (Nigg et al., 2004
) but did at ages 15 to 17 (Nigg et al., 2006
) is consistent with such an account.
Another possible explanation for the absence of direct relations between ECFs and drug use in adolescents is that youth with poor working memory are more susceptible to the interfering effects of drugs on their behavior (Finn, Justus, Mazas, & Steinmetz, 1999
). As a result, they are more susceptible to developing dysfunctional trajectories of drug use. Thus, deficits in working memory and other ECFs might not correlate with drug use and SUD until later in life after the deleterious effects of working memory limitations have had their effect. This explanation is consistent with the findings of Tarter et al. (2003)
that early ECF did not predict drug use at age 16 but did predict SUD at age 19.
Age Related Changes in Risk Behavior and ECF
One finding that stands out in the pattern of age related differences in risk behavior is that although our sample of preadolescents tends to exhibit increasing risk behavior with development, they also exhibit increasing development of working memory. This pattern suggests that engaging in risk behavior is related to cognitive maturation and that exploring these risks is part of the natural development of adolescents. The finding that better working memory and reversal learning are related to less impulsivity suggests that the continued development of these capabilities may eventually overcome the adverse influences of impulsive tendencies, perhaps leading to their decline.
Implications for Intervention
Depending on the ultimate relations we observe between impulsivity, ECF, and risk behavior, we will draw different conclusions about appropriate interventions to reduce the risk of excessive engagement in potentially addictive and harmful behaviors. If ECF eventually matures to the point where it begins to control heavy use of drugs, then efforts to improve ECF should be a focus. However, if impulsivity is the major contributor to excessive drug use, then other strategies may be needed. There is evidence that training of life skills can reduce drug use (Botvin & Schenke, 1997
), but less is known about how well these skills can control drug use for those with high levels of impulsivity. Future research may need to focus on this question, especially if ECF proves not to be critical to drug use prevention.
If drug use during adolescence retards the development of ECF and this enhances the risk for emergence of SUD and other disorders, then efforts to prevent early drug use itself will be a major focus of attention. Indeed, national campaigns to prevent drug use emphasize this trajectory. This explanation is consistent with considerable research indicating that drug abusers exhibit deficits in reward processing (Bechara, 2004
; Bechara & Martin, 2004
; Goudriaan, Grekin, & Sher, 2007
). It is also possible, however, that early impulsive and disruptive behavior leads to the use of drugs that then interferes with the normal development of age appropriate ECF. From the perspective of this explanation, early intervention to treat impulsive and disruptive behavior should reduce the likelihood of progressing on the dysfunctional trajectory.
In addition to these two explanations, it is also possible that early manifestations of risk for SUD and conduct disorder are mere markers for a developmental path that unfolds whether preadolescents use drugs or not. For example, Prescott, Aggen, & Kendler (1999) find using twin data that early use of alcohol does not add increased risk of later alcohol dependence above the effects of genetic predispositions to alcohol abuse. Other genetically-informed research also suggests that early substance use is more environmentally driven while later emergence of dependence and problems with drugs is more under the influence of genes (McGue et al., 2006
; Pagan et al., 2006
). From this perspective, discouraging early use of drugs and other risky behavior may not be the best strategy; instead interventions that enhance the control of underlying impulsive tendencies may be more successful in reducing the development of risk-behavior trajectories.