We found that cocaine-dependent subjects showed an attentional bias to cocaine-related words expressed as a significantly larger RT difference (cocaine-related words – neutral words), confirming the increased salience of cocaine-related stimuli in this population (3
). We also found an increased IMT commission error rate and BIS-11 scores in cocaine-dependent subjects compared with controls, suggesting impaired inhibitory control and increased impulsivity in cocaine-dependent subjects, which is consistent with previous studies (8
). The most important finding of the study, however, was the observed association between attentional bias and inhibitory control, as measured by IMT commission error rate, in cocaine-dependent subjects. At a theoretical level, it is possible that individuals with poor inhibitory control are less able to engage strategic processes to override the attentional bias. This finding is consistent with a recent study (20
) showing a positive correlation between the alcohol-related attentional bias and impulsive decision-making in a delay discounting task in heavy drinking adolescents. The significant association between attentional bias and inhibitory control supports the hypothesis that “substance abusers with severely compromised inhibitory control are particularly susceptible to the attention-grabbing properties of substance-related stimuli” (18
, p 12), although further research is needed to delineate the nature of the relationship between attentional bias and inhibitory control.
Cognitive deficits in cocaine-dependent subjects have been examined using neuroimaging techniques (10
). When cocaine-dependent subjects performed the cocaine Stroop task, task performance produced hypoactivation in the rostro-ventral anterior cingulate cortex (ACC)/medial orbitofrontal cortex compared with baseline activity (21
). This change in brain activity was larger in cocaine-dependent subjects than controls (22
) and was larger when the cocaine-dependent subjects were exposed to cocaine-related words than when they were exposed to neutral words (21
). Similar results were obtained in ACC using the Stop Signal and Go/NoGo tasks (23
). It follows that ACC activity may underlie the significant correlation between attentional bias to cocaine-related words and the IMT commission error rate in cocaine-dependent subjects found in the present study.
No significant correlation between attentional bias and drug use behaviors (total years, days in past 30 days and age to start cocaine use) was observed in cocaine-dependent subjects. Similarly, Hester et al. (3
) did not find a relationship between attentional bias and drug use history in cocaine-dependent subjects. However, among users of alcohol or cannabis, attentional bias to drug-related cues was higher in heavy users than in light users (18
). In our study, all cocaine users were cocaine-dependent subjects. Perhaps no further increments in attentional bias occur once cocaine users have reached the state of dependence. Consistent with this, in heavy cannabis users there was no significant relationship between the user’s quantity or frequency of cannabis use and the degree of their attentional bias (18
Consistent with Vadhan et al. (4
), we also found that treatment-seeking cocaine-dependent subjects had a higher attentional bias to cocaine-related words than non-treatment-seeking cocaine-dependent subjects. This difference in attentional bias may be related to other factors that differ between treatment-seeking and non-treatment-seeking cocaine-dependent subjects, such as variance in the adverse consequences of cocaine use (26
). Further research is needed to investigate this relationship.
One major limitation of the current study is that there were significant differences in age and gender distribution between control and cocaine-dependent subjects. However, for the controls, we did not find a significant correlation between age and attentional bias (r = −0.05, p = 0.77) nor between age and impulsivity (for age and BIS-11 total score, r = 0.08, p = 0.64; for age and IMT commission error rate, r = 0.04, p = 0.81). Furthermore, we did not find a significant difference in attentional bias or impulsivity between female and male subjects. Covariance analysis with age and gender as covariates also did not change the significance of the outcomes. Future studies of attentional bias may benefit from greater control over the sociodemographic variables, as well as more detailed quantitative information regarding recency and amount of cocaine use and use of other drugs. Another limitation is that we did not exclude cocaine-dependent subjects with marijuana or alcohol dependence because of the high percentage of marijuana and alcohol dependence in this population. We did exclude subjects whose urine THC screening or breath alcohol test was positive before behavioral tests to exclude potential acute effects of marijuana or alcohol on performance during behavioral tests. Discrepancies in the proportion of current cigarette use between cocaine-dependent (80%) and control subjects (14%) is also a potential confounding factor in the difference on behavioral test performance between the two groups. Future studies will need to attend carefully to nicotine use across all subject groups
In summary, the present study showed that cocaine-dependent subjects had an attentional bias to cocaine-related words, poorer inhibitory control measured by the IMT, and higher impulsivity measured by BIS11. Attentional bias was positively correlated with the commission error rate in the IMT. This positive correlation between attentional bias and inhibitory control suggests that a potential behavioral mechanism of impaired inhibition may underlie poor clinical outcomes in impulsive cocaine users, although further research is warranted to elucidate this mechanism. Behavioral techniques and medications aimed at improving impulse control and remediating attentional bias may prove to be helpful tools in the treatment of cocaine dependence.