By Marion Torchia, NIDA NOTES Contributing Writer
Researchers at the University of Pittsburgh's Center for Education and Drug Abuse Research have identified a set of characteristics that appears to predict a boy's vulnerability to substance use disorder (SUD) in young adulthood. Once validated for use with the general population, this new construct, "neurobehavioral disinhibition," may help clinicians tailor drug abuse prevention programs for children most in need of support.
Under the direction of Dr. Ralph E. Tarter, the researchers have conducted comprehensive longitudinal studies to understand how neurobehavioral disinhibition may relate to the genetic, biological, psychological, and environmental factors that are thought to predispose individual boys to SUD. They have developed an index that links the set of personality characteristics to a quantitative scoring system. The index appears to identify as early as age 10 children who are especially vulnerable to drug problems in adolescence.
Neurobehavioral disinhibition comprises a cluster of emotional tendencies, behavioral symptoms, and problems in cognitive function that indicate that a child has not adequately developed psychological self-regulation, a capacity that depends on normal neurological development (see "Neurobehavioral Disinhibition: A Closer Look").
According to Dr. Tarter, the construct's key strength is its biological basis: Its elements closely relate to what is known about the brain's development. "Neurobehavioral disinhibition points to deficiencies in those higher level brain functions—self-control and deliberate, goal-directed action—that we know are managed in the prefrontal cortex."
According to Dr. Kevin Conway, director of the Program on Antisocial Behaviors and Related Vulnerability in NIDA's Epidemiology Research Branch, Dr. Tarter's research shows that the construct actually works. He notes that Dr. Tarter and his colleagues followed the same group of children for more than a decade and that "the children's early scores for neurobehavioral disinhibition predicted with amazing accuracy whether or not they would develop SUD and how severe their problems would be." He adds that "Dr. Tarter's study takes earlier research on vulnerability to drug abuse a step forward and points to particular components of a person's biological makeup that may be at the root of the problem."
Construct Developed, Tested
To develop their construct and its numerical scoring system, Dr. Tarter's group tracked from childhood to young adulthood 47 boys at high average risk and 65 boys at low average risk of SUD based on their status as biological offspring of fathers with or without SUD as defined by the American Psychiatric Association's diagnostic criteria (DSMIII-R). The investigators limited this particular study to boys because the girls in their longitudinal research program were enrolled later and had not been followed long enough to make valid predictions and match the outcomes to them.
Researchers hope that early identification and treatment of neurobehavioral disinhibition can help at-risk children develop self-control and avoid drug initiation and abuse.
The neurobehavioral disinhibition construct was developed by assessing the children in the study using a series of existing tools that measure dysregulated emotions, behavioral undercontrol, and executive (higher order) cognitive capacity. To measure emotion, for example, the researchers used the "difficult" temperament index from the Revised Dimensions of Temperament Survey. They measured behavior "undercontrol" using two diagnostic tools, the Schedule for Affective Disorders and Schizophrenia for School-Age Children, as rated by the children's mothers, and the Disruptive Behavior Disorders Rating Scale, as measured by their teachers. A battery of neurological tests measured cognitive processes that depend on the prefrontal cortex.
The next step, verifying the construct by a statistical technique called factor analysis, confirmed that the separate components of neurobehavioral disinhibition—personality style, behavior, and brain function—tend to occur together. This suggests that neurobehavioral disinhibition is driven by a single process involving prefrontal cortex functioning. Says Dr. Tarter, "We are looking at the integrity of the brain by measuring its activities."
Index Predicts SUD Vulnerability
To test the hypothesis that the neurobehavioral disinhibition score is correlated with expected risk of future SUD, Dr. Tarter's team compared the scores of the high-risk boys in the study with those of the low-risk boys. The boys at higher risk had significantly higher scores at ages 10 to 12 on several, though not all, of the component indicators of neurobehavioral disinhibition. When the boys were tested again at age 16, the higher risk boys had scores consistent with neurobehavioral disinhibition on every component indicator of the trait.
Moreover, the boys' disinhibition scores at ages 10 to 12 predicted with nearly 70-percent accuracy whether they would actually develop SUD by age 19. Even more strikingly, their disinhibition scores at age 16, combined with their frequency of drug use in the previous 30 days, predicted with 85-percent accuracy their likelihood of developing SUD by age 19. In fact, the boys' disinhibition scores at age 16 were better predictors of SUD at 19 than the frequency of their drug use at age 16. In addition, their disinhibition scores were strongly predictive of the general severity of their problems as measured by the "overall problem density score" on the revised Drug Use Screening Inventory. This score includes health, behavior, school, family, and social adjustment problems.
The scores have both positive and negative predictive value, according to Dr. Tarter's research report. However, some of the data indicate that a high disinhibition score predicts that a boy will have SUD with a greater degree of probability than a low score predicts that he will avoid the disorder. The boys' high scores at age 16 predicted future SUD with 97-percent accuracy; on the other hand, low scores at this age predicted with only 61-percent accuracy that SUD would not develop.
Value of Findings Cited
"From NIDA's perspective, this research is a long-term investment," notes Dr. Conway. "Because it is a longitudinal study, Dr. Tarter and his colleagues have been able to gather a broad range of information about the boys, so that the effect of the multiple factors known to be related to SUD can be traced over time."
The next phase of the study will be especially interesting, because the first group of boys will have entered young adulthood, when SUD most often emerges. The researchers will continue to track the young men even as new participants join the study.
The findings should not be assumed to apply to all children, Dr. Tarter cautions. Before the trait can be considered universally valid and ready for use in working with children, much larger studies will be needed involving the general population, including both genders and diverse ethnic and socioeconomic groups.
"It is important that our new knowledge be used to bring about constructive change," Dr. Tarter adds. "An index of neurobehavioral disinhibition has potential value because it offers an opportunity to monitor children's development and detect those children with significant deviations, who may be at heightened risk of SUD. If teachers, counselors, and parents can identify a child's problems early, they can structure environmental conditions to promote a healthy outcome and avoid the path to SUD."
Neurobehavioral Disinhibition: A Closer Look
The construct developed by Dr. Tarter and his colleagues includes many symptoms that characterize attention-deficit/hyperactivity disorder, conduct disorder, and oppositional defiant disorder. But it reaches beyond those diagnostic categories to describe emotional states and neurological capacities as well as their behavioral manifestations.
Compared to his peers, a "disinhibited" child can be described as "difficult." His (or her) moods are volatile, and he often exhibits restlessness and an inability to persevere in a task. Poor self-management often reveals itself in risky, even reckless behavior. Neurological tests reveal a lack of certain capacities that originate in the part of the brain that manages higher level thinking. Three dimensions of his problem are especially important:
- "Difficult" temperament. A disinhibited child is irritable and easily thrown off balance and has a harder time than other children returning to a comfortable emotional state after a stressful or arousing experience. His emotions seem to be more intense than those of his peers. These characteristics commonly provoke negative responses from adults and other children. If so, a vicious cycle can develop, and the child's reactions can become more extreme as time goes on.
- Undercontrolled behavior. The disinhibited child's behavior is chronically out of touch with the demands of the situation. He or she has a hard time meeting a school's learning requirements and does not relate easily to either adults or peers. He may engage in "externalizing behavior" or "acting out," typically through disruptiveness, unprovoked aggression, defiance of authority, or delinquency. His behavior is also marked by impulsivity and an inability to persist in pursuing his goals.
- Deficiencies in complex brain functions. The prefrontal cortex in the human brain manages an individual's purposeful activities. It is possible to measure a child's ability to pay attention, to remain aware of what is going on in the environment, and to complete a task or a coordinated sequence of actions. For example, researchers can see whether a child can turn away from a signal and deliberately look in the opposite direction when asked to do so. A disinhibited child will have trouble with this simple task, which requires deliberate control over eye movement, a capacity that resides in the prefrontal cortex.
Tarter, R.E., et al. Neurobehavioral disinhibition in childhood predicts early age at onset of substance use disorder. American Journal of Psychiatry 160(6):1078-1085, 2003.
Volume 19, Number 2 (July 2004)