Elsevier

Neuropsychologia

Volume 38, Issue 8, July 2000, Pages 1180-1187
Neuropsychologia

Drug abusers show impaired performance in a laboratory test of decision making

https://doi.org/10.1016/S0028-3932(99)00158-XGet rights and content

Abstract

A defining feature of drug addiction is persistent drug use despite long-term adverse consequences. This study examined the performance of drug abusers on a neuropsychological test that requires evaluation of long-term outcomes in the presence of a complex set of mixed reward/punishment contingencies (the Gambling Task). In order to control for generalized deficits related to choice and planning, subjects were also administered the Wisconsin Card Sorting Task. Thirty polysubstance abusers were compared to a comparison group of 24 subjects who did not use illicit drugs of abuse. Drug abusers performed much more poorly on the Gambling Task (net score = 10.2 ± 4.7, mean ± s.e.m.) than controls (26.0 ± 5.3), but did not differ from controls on the Wisconsin Card Sorting Task. The results show that drug abusers are more likely to make maladaptive decisions in the Gambling Task that result in long-term losses exceeding short-term gains. These findings indicate that the Gambling Task may be a useful model in laboratory studies of cognitive dysfunctions associated with drug abuse.

Introduction

Persistent drug use despite adverse health and social consequences is central to the definition and diagnosis of addiction. Accordingly, the DSM IV criterion for substance abuse disorder is “continued [substance abuse] despite knowledge of having a recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance” (p. 181) [2]. Similarly, WHO definitions of disorders due to psychoactive substance use include the criterion of “persisting [use]... despite harmful consequences” (p. 321) [1]. Impairments in decision-making capabilities may stand at the core of substance abuse, and cognitive tasks that would permit study of such a dysfunction under controlled conditions could provide an important advance in the understanding of addiction.

The Gambling Task tests the ability to balance immediate rewards against long-term negative consequences, and therefore has strong face validity for evaluating a cognitive deficit that may contribute to drug abuse. This task was originally developed to delineate the impairment of patients with frontal lesions centered on (but not restricted to) the ventromedial prefrontal cortex (VmPFC) [9], [10]. These patients exhibit poor judgment in business and personal decisions and act in a generally irresponsible manner, but perform normally on standard intelligence and neuropsychological tests, including tests of social knowledge and executive function, such as the Wisconsin Card Sorting Task (WCST) [9], [10], [19], [20], [23], [47].

The goal of this study was to determine whether drug abusers are impaired on the Gambling Task compared to a group of non-drug using individuals. A secondary goal was to make an initial determination of whether impairment on the Gambling Task might be due to a generalized frontal lobe dysfunction. The Wisconsin Card Sorting Task was chosen as a comparison test since it also involves higher order executive functions related to choice and planning. The Wisconsin Card Sorting Task has a different neuropsychological profile as it is sensitive to damage of the dorsolateral portion of the prefrontal cortex, as well damage to non-prefrontal cortical regions connected to the prefrontal cortex, e.g. parietal cortex [4], [5], [12], [26], [35], [43]. On the other hand, the Gambling Task is sensitive to damage of the ventromedial prefrontal cortex, but not the dorsolateral prefrontal cortex [9], [10], [47]. Therefore, if drug abusers have a generalized frontal dysfunction it should result in poor performance on both the Wisconsin Card Sorting Task and the Gambling Task. Alternatively, poor performance on the Gambling Task but not the Wisconsin Card Sorting Task would provide a preliminary neuropsychological foundation for hypothesizing that drug abusers have a dysfunction in the ventromedial rather than the dorsolateral aspects of the prefrontal cortex.

Section snippets

Methods

Subjects for this study were male and female volunteers, aged 21 to 44 years, recruited through newspaper advertisements as described before [29]. They were given a comprehensive medical screening, including a structured psychiatric evaluation (Diagnostic Inventory Survey) and a test of current intellectual functioning (Shipley Institute of Living Scale) [53]. All potential subjects (controls and drug abusers) with a history of head trauma, or lifetime Axis I psychiatric diagnoses other than

Subjects

The study sample consisted of 30 drug abusers and 24 controls. Demographic characteristics of the sample are given in Table 1, and drug use is shown in Table 2, Table 3. The mean age of the drug abusers (35.2 ± 0.9 years old; mean ± standard error ) was significantly higher than that of the controls (31.0 ± 1.3) (t52=2.78, p<0.01). The average years of education of drug abusers (13 ± 0.3 years) was also significantly different from that of the controls (14.3 ± 0.4) (t52=−2.62, p<0.01), but

Discussion

The present results support the hypothesis that drug abusers are selectively impaired on the Gambling Task, since they do not differ from controls on another neuropsychological task of higher cognitive function (Wisconsin Card Sorting Task). The data support the face validity of the Gambling Task as a model for a critical aspect of addictive behavior: persistence of a positively rewarded behavior despite adverse consequences [1], [2]. Furthermore, these results suggest a hypothesis regarding

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    A preliminary report of this study was presented at the 27th Annual Meeting of the Society for Neuroscience in New Orleans, LA on October 26, 1997.

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