Increased impulsivity in cocaine dependent subjects independent of antisocial personality disorder and aggression

Abstract

Several previous studies show a relationship between impulsivity and substance abuse; however, it is unclear whether the increased impulsivity seen in substance dependent groups is specifically related to substance abuse, or if it is due to concomitant antisocial personality disorder (ASPD) or aggression. The issue of whether impulsivity is specifically related to substance abuse is important since it has a bearing on risk factors for development of substance abuse. To determine whether cocaine dependent subjects show increased impulsivity independent of ASPD, the Barratt impulsiveness scale (BIS-11), a delayed reward laboratory measure of impulsivity, and the life history of aggression scale were administered to 49 cocaine dependent subjects and 25 controls. Results showed that cocaine dependent subjects with ASPD were more impulsive and aggressive than controls, but cocaine dependent subjects without ASPD were also more impulsive compared to controls. Controlling for aggression history, cocaine dependent subjects without ASPD continued to have elevated impulsivity as measured by the BIS-11, but not the delayed reward task. This study supports the hypothesis that the increased impulsivity as measured by the BIS-11 in cocaine dependent individuals is not exclusively due to concomitant increases in aggression or ASPD.

Introduction

There is a growing body of literature linking impulsivity, aggression, and substance abuse. As reviewed by Brady et al. (1998), prior studies find that impulsive and aggressive individuals have a higher rate of substance abuse than the general population. Studies measuring impulsivity in substance abusing individuals have used a variety of methods to determine the level of impulsivity. One method used to measure impulsivity is self-report questionnaires, such as the Eysenck Impulsiveness Questionnaire (Eysenck et al., 1985), or the Barratt impulsiveness scale (Patton et al., 1995). Since self-report measures of impulsivity ask about long-term patterns of behavior, they are considered to be more of a trait than a state measure of impulsivity (Moeller et al., 2001). Studies using self-report measures find elevated impulsivity in substance users compared to controls (Moss et al., 1990, Patton et al., 1995, Allen et al., 1998). Another method that has been used to quantify the level of impulsivity in both animals and humans is behavioral laboratory tasks. Since behavioral laboratory measures of impulsivity can be changed on an acute basis by factors such as drug administration (Dougherty et al., 2000), they are considered to be more of a state measure of impulsivity (Moeller et al., 2001). One such task commonly used as a measure of impulsivity involves the choice (either theoretical or actual) between a larger delayed reward and a smaller more immediate reward. In this type of task, the choice of the smaller more immediate reward is considered to be a measure of impulsivity, and the choice of a larger delayed reward is a measure of self-control. Studies that used delayed reward tasks found that substance using individuals are more likely to choose the immediate (impulsive) reward compared to non-substance using individuals (Madden et al., 1997, Vuchinich and Simpson, 1998, Kirby et al., 1999, Mitchell, 1999). Other studies using self-report and behavioral laboratory measures of aggression find increased aggression in substance abusing individuals compared to controls (Fishbein and Reuland, 1994, Moeller et al., 1994, Allen et al., 1997). Likewise, there is an increased incidence of antisocial personality disorder (ASPD) in substance dependent populations that is also associated with impulsivity and aggression (reviewed in Moeller et al., 2001). However, few studies have attempted to examine both ASPD and aggression in relation to impulsivity to determine if the increased impulsivity seen in substance dependent individuals is more related to these other factors than to substance abuse per se. Thus, the exact relationship between impulsivity and substance abuse is clouded by other mediating factors such as concomitant aggressive behavior and ASPD.

The controversy surrounding the relationship between impulsivity and substance abuse is illustrated in studies of adolescent risk factors for later development of substance abuse. Some studies find a higher rate of later development of substance abuse among individuals with childhood disorders that are associated with elevated impulsivity (ADHD and conduct disorder) (Moss and Lynch, 2001, Sullivan and Rudnik-Levin, 2001). Other studies argue that the later development of substance abuse is related to conduct disorder alone (Lynskey and Hall, 2001), or to childhood aggressive behavior (Brook et al., 1992, Reinherz et al., 2000). Related studies of adults with cocaine dependence find that between 10 and 30% of cocaine dependent individuals meet diagnostic criteria for ADHD (Carroll and Rounsaville, 1993, Levin et al., 1998, Clure et al., 1999). However, cocaine dependent individuals with ADHD are significantly more likely to also meet criteria for ASPD and conduct disorder (Levin et al., 1998).

Another possible mechanism for an association between cocaine use and impulsivity is through the effects of cocaine on brain function. Cocaine has effects on dopamine and serotonin neurotransmitter systems which are important in the initiation and control of behavior (Cunningham et al., 1992, Levy et al., 1992, Levy et al., 1993, Buydens-Branchey et al., 1999, Jentsch and Taylor, 1999). In light of the effects of cocaine on brain function and the general finding of increased impulsivity in substance dependent individuals, there is support for an association between cocaine misuse and impulsivity independent of ASPD or aggression.

The purpose of this study was to determine whether impulsivity was increased in cocaine dependent subjects after statistically controlling for concomitant aggression and ASPD, using a self-report and a behavioral laboratory measure of impulsivity. The hypotheses of the study were: (1) Impulsivity would be increased in cocaine dependent subjects both with and without ASPD compared to controls. (2) Controlling for aggression, cocaine dependent subjects without ASPD would have higher impulsivity than controls.