Varieties of Impulsivity: Evidence from Animal Studies
John L. Evenden, Ph.D., D.Med.Sci., AstraZeneca

Dr. John Evenden presented a series of drug studies in which rats were used to examine the relationships among the stimulus, response, and reinforcer in the traditional three-term contingency of decisionmaking. The studies revealed that different aspects of impulsivity are differentially sensitive to different drugs and that the effects of drugs depend, in part, on the strain of rat used. Therefore, it can be concluded that impulsive behavior is modulated by a complex interaction of trait factors, such as genetics and personality, and state factors, such as drug treatment. Further, drugs’ effects can vary dramatically if self-control is prompted by negative reinforcement or punishment.

Behavioral Models of Impulsivity in Humans and Nonhumans: Effects of Drugs
Harriet de Wit, Ph.D., University of Chicago

Dr. Harriet de Wit discussed studies implying that there are at least two separate processes underlying impulsive behaviors – impairments in decision making and planning and impairments in behavioral inhibition. Her team used human and nonhuman laboratory models to investigate these processes and concluded that, while delay discounting procedures and the stop task are both valid methods for measuring impulsive behavior, delay discounting and behavioral inhibition reflect separate processes. De Wit stated that these findings are a starting point for identifying both the underlying factor structure and the neurobiology of impulsive behavior.

Neurobiological Changes Related to Impulsivity as a Consequence of and an Added Risk Factor for Psychostimulant Abuse
F. Gerald Moeller, M.D., University of Texas Health Sciences Center

Dr. Gerald Moeller presented a review of the literature and new data on the associations among psychostimulant abuse, impulsivity, and brain function, which show that impulsivity appears to be a risk factor for stimulant abuse. Further, impulsivity is associated with changes in brain function, and these changes are potentially related to the chronic effects of stimulants. This information provides a foundation for research that will investigate potential treatments for impulsivity and associated stimulant abuse.

P3 Event-Related Potential Amplitude and the Risk for Disinhibitory Behavior Disorders
William G. Iacono, Ph.D., University of Minnesota

Dr. William Iacono discussed the relationships among externalizing psychopathologies that are indicative of behavioral disinhibition. He described a study in which P3 amplitude elicited from a visual oddball task in a population-based sample of a group of 17-year-old males and females. Reduced P3 amplitude in males was associated with the presence of ADHD, conduct disorder, and substance use disorders, as well as with the presence of substance use disorders in their parents. For females, reduced P3 amplitude was associated with having a substance use disorder only. These findings suggest that a dimension of disinhibitory psychopathology indexed by reduced P3 amplitude underlies the relationship among childhood externalizing and substance use disorders, especially in males.