Impulsivity is a risk-factor associated with substance use disorders. On paper-and-pencil measures, people with comorbid psychotic disorders and substance abuse have been shown to be more impulsive than their non-using counterparts. However, there has been little research on the behavioral components that, collectively, define the construct of impulsivity, which have been identified as: temporal discounting, risk taking, underestimating time, and failure to inhibit extraneous responding. This study compared people with psychotic disorders who did and did not use cocaine on behavioral measures of these components. One group (COC-now) had a positive urine drug screen (UDS) for cocaine (N = 20). A second group (COC-past) had a negative UDS, but a positive cocaine history (N = 20). Finally, the third group (control) had no history of cocaine use (N = 20). Those with a current or past history of cocaine use engaged in more risk-taking behaviors and seemed to be less affected by anticipated loss and more attuned to monetary gains. However, contrary to our hypothesis, patients in the COC-now group selected larger, delayed rewards over the smaller, immediate rewards. Performance on the immediate/delay task also suggested greater attentiveness to the magnitude of the monetary reward for patients with a positive UDS.
People with a diagnosis of schizophrenia spectrum disorders have higher rates of substance use than the general population or groups characterized by other psychiatric disorders, ranging from 33% to 50% (Blanchard et al., 2000). Of particular concern is abuse and dependence of psychostimulants. Several studies have found that the frequency of cocaine use among people with schizophrenia was 27% higher than use of other substances (Sevy et al., 1990, Shaner et al., 1995 and Genata et al., 2001). Cocaine use among people with psychotic disorders leads to poorer treatment outcomes, more severe psychiatric symptoms (including positive symptoms), increased rates of treatment noncompliance, violence, HIV infection, homelessness and higher medical costs (Genata et al., 2001). Given the association of schizophrenia spectrum disorders with substance dependence in general, and psychostimulant use in particular, it is important to better understand the psychological mechanisms that predispose to drug use. One candidate mechanism is impulsivity.
Few studies have examined impulsivity in clinical populations (Kjome et al., 2010) and the neural correlates of impulsivity in people with schizophrenia are not well understood (Kaladjian et al., 2010). Even though impulsivity has been found to characterize people with substance use disorders alone (Hollander & Rosen, 2000 and Whiteside & Lynam, 2001), this construct is not well understood and often is used to refer to various and separable response tendencies (Dervaux et al., 2001). Therefore, this study adopted a multivariate approach to examine impulsivity in people with both psychotic disorders and substance dependence. Specifically, we assessed the following components: a) temporal discounting (whether a person chooses smaller, immediate rewards over larger, delayed rewards); b) risk taking (probability people who engage in risk-taking behaviors are concerned with the risk of injury versus the potential for rewards); c) underestimating time and; d) failure to inhibit extraneous responding (responding prematurely or having the inability to withhold a response). These measures were chosen based on published reports that substance abusers in the general population tend to: 1) discount the value of delayed rewards (Moeller et al., 2001, Petry, 2001, Holt et al., 2003 and Murray et al., 2003) and tend to choose the smaller, more immediate alternatives compared to the larger, delayed reward-tendencies also found in animal studies of substance dependence (Madden et al., 1997, Vuchinich & Simpson, 1998, Kirby et al., 1999, Crean et al., 2000, Odum et al., 2000, Moeller et al., 2001, Petry, 2001, Holt et al., 2003 and Murray et al., 2003); 2) engage in more risk-taking behaviors (Zuckerman et al., 1990, DiClimente, 1993 and Lejuez et al., 2002); 3) underestimate the span of time (White et al., 1994 and Zimbardo et al., 1997; 4) fail to inhibit extraneous responding (Fillmore and Rush, 2002). In summary, we examined whether people with psychotic disorders who currently use cocaine relative to patients who only have a history of cocaine or no use at all are more impulsive, operationally defined as discounting delayed rewards, choosing riskier alternatives, underestimating the span of time and/or failing to inhibit extraneous responding.
