In this sample of participants receiving behavioral therapy in the context of a randomized clinical trial, we found that treatment outcome status, i.e., abstinent or nonabstinent from cocaine for 2 or more weeks, was associated with different neurocognitive profiles measured at baseline. Abstinent subjects were more impulsive, as measured by the BIS non-planning scale, while, at the same time, more likely to use advantageous decision-making strategies, as measured by the IGT. The results for the BIS differ from a previous study by our group which did not use CM or CBT and found that higher impulsivity was associated with a poorer treatment response14
Based on the therapy design for this study, we expected that higher impulsivity, which is related to choice of immediate over delayed rewards15
, would positively predict responding to the immediate monetary-based rewards offered as part of contingency management. Likewise, we hypothesized that decision-making on the IGT, which involves responding flexibly to changing contingencies, would be associated with favorable response to CM. Finally, we proposed that having more intact cognitive processes would facilitate responding to CBT skills training. Our findings support this notion that monetary incentives combined with skills training may be a strong treatment intervention for a subgroup of impulsive cocaine patients. Without a therapy control condition, we cannot determine the relative efficacy of CM with CBT over other behavioral or nonbehavioral treatment interventions. Nevertheless, our findings contribute to a growing literature of studies reporting a significant relationship between baseline neurocognitive function and clinical outcome in drug using patients following treatment41, 42
. Further investigation of the specific efficacy of behavioral treatment for targeting impulsivity in cocaine dependent subjects is needed.
The role of impulsivity in the initiation and maintenance of stimulant abuse has drawn increasing attention. Notions of impulsivity have emphasized lack of inhibition, rapid responding, lack of persistence, inattentiveness, and failure to delay reward gratification 15, 43
. In this study we observed that self-reported indexes of nonplanning impulsivity were associated with cocaine abstinence, whereas indexes of attentional, motor, and inhibitory-control components of impulsivity, as assessed by the IMT/DMT and the BIS-11, failed to predict treatment retention or demonstrate a difference as a function of cocaine abstinence. These measures have previously shown differences between normal controls and cocaine users 44
. The lack of influence on these processes on treatment response suggests that not all components of impulsivity are equally predictive of treatment response.
The current report has several limitations. First, measures of impulsivity and decision making were not fully representative of these domains. A measure of delay of reward gratification, such as a delay discounting procedure, would have strengthened our findings. Moreover, other indexes of executive function, such as the Wisconsin Card Sort task, would have provided more evidence of the role of decision making in treatment response. As mentioned earlier, no treatment condition was included without CM and CBT, making conclusions about the role of behavioral interventions tentative. That abstainers were more likely to remain in study than non-abstainers means that level of exposure to, and participation in, therapy varied, which may have also confounded interpretation of the findings. Statistically, the lack of interaction between medication condition and behavioral measures could have been a function of power; the idea that differential profiles for outcome groups are themselves moderated by treatment condition remains plausible. Finally, the current sample was restricted to a narrow range of severe cocaine users, and inclusion of the full continuum of cocaine abusers might have altered the current results.
In summary, this study found that neurocognitive profiles, obtained from cocaine dependent subjects at baseline, differed as a function of treatment outcome. Subjects who achieved at least 2 weeks of abstinence had higher non-planning impulsivity scores and better decision-making performance at baseline than subjects who failed to achieve abstinence. These differences were observed within the context of a behavioral therapy platform designed to target impulsivity. While these findings cannot establish a causal relation between cognitive function at baseline and response to specific therapeutic interventions, they permit speculation regarding appropriate treatment-matching strategies and underscore the need for future confirmatory research.