Cocaine-dependent subjects showed higher scores on the BIS, more commission errors on the IMT, and a preference for disadvantageous decks on the IGT compared to non-drug using controls. There also was a significant correlation between commission errors on the IMT and BIS scores. There was no significant correlation between IGT net scores or EVM parameters and the impulsivity measures.
On the IGT, cocaine-dependent subjects shifted to advantageous decks more slowly and to a lesser degree than controls. This is compatible with previous findings for the IGT in cocaine users (Verdejo-Garcia et al., 2007a
). In the EVM analysis, the consistency parameter was lower in cocaine-dependent subjects. Valence (motivation) and updating (learning) were not significantly different in cocaine-dependent subjects. These findings are partially consistent with those from Stout et al. 2005
, which found consistency (choice) and valence (motivation) to be significantly different between cocaine users and controls. There were no significant correlations between EVM model parameters and BIS or IMT/DMT.
As seen in previous studies examining outcomes of behavioral paradigms assessing attention, impulsivity, and response inhibition in cocaine dependent subjects, cocaine dependent individuals showed deficits related to increased impulsivity, decreased response inhibition and decreased attention (Moeller et al., 2005
, Garavan et al., 2008
, Colzato et al., 2007
, Lane et al., 2007
). Previous studies have also shown that decision-making as assessed through various paradigms is influenced by cocaine use and dependence (van der Plas et al., 2008
, Green et al., 2009
, Verdejo-Garcia et al., 2007a
, Strickland et al., 1993
). However, previous studies have not assessed correlations between these various measures of impulsivity, response inhibition and decision-making in this specific population. Previous studies have looked at “substance dependent populations” (multiple substance types) or cocaine users as a subset of other populations, with fewer looking at cocaine dependent populations specifically. Previous studies by Stout et al. employing EVM analysis of IGT performance in cocaine dependent subjects have shown similar outcomes on EVM parameters, but had smaller samples of cocaine dependent subjects (Stout et al., 2004a
Analyzing our findings in light of previous EVM analysis in cocaine dependent subjects (Stout et al., 2004a
), our findings partially replicate the previous findings, which showed consistency and valence to be lower in cocaine dependent individuals compared to controls. Our findings are also similar to findings in patients with bilateral ventromedial prefrontal cortex (vmPFC) lesions, who had decreased degree of consistency and update rate on EVM analysis (Yechiam et al., 2005
). This may represent prefrontal gray matter volume loss observed in substance dependent people (Tanabe et al., 2009
The results of examination of correlations between questionnaire measures of attentional, motor, and nonplanning impulsivity and response inhibition as well as decision-making joins a group of previous studies examining the relationship between different components of impulsivity and decision making in different subject groups. Previous studies have also described a non-correlating or partially correlating relationship between measures of impulsivity and decision-making. Examining the relationship between similar decision-making tasks (Delay Discounting Procedure or DDP, Gambling Task or GT, and Rogers Decision-Making Task or RDMT) in substance abusers, Monterosso et al. found GT performance correlated with DDP performance, response time on RDMT correlated with GT and DDP performance, and no task was observed to correlate with measures of impulsivity (Monterosso et al., 2001
). They attribute these findings to the similarity of the constructs they were measuring; risk, delay, and impulsivity, which overlapped with one another, but may require more refinement in their assessment. A correlation between measures of trait impulsivity and commission errors on a behavioral measure of motor impulsivity (go/no-go task) and lack of correlation between trait impulsivity and decision-making, delayed discounting, reflection impulsivity and self-regulation was also observed in a sample of high and low trait impulsivity women (Perales et al., 2009
). There have been other studies that have described a relationship between measures of impulsivity and decision-making. In a study comparing 50 adults with ADHD with 51 controls, there was a negative correlation with BIS-11 nonplanning and net scores on IGT second, third, fourth and fifth blocks, a negative correlation between IGT total net score and BIS-11 nonplanning subscale, and BIS-11 total score negatively correlated with the difference between advantageous and disadvantageous choices in the second and third block of the IGT (Malloy-Diniz et al., 2007
). The difference in correlation between IGT and BIS-11 in this population compared with our cocaine-dependent sample may result from differences in the presentation of impulsivity, nonplanning and decision-making in these two populations, as well as inclusion of combined- type ADHD in that study. To compare the findings of the current paper to those of Malloy-Diniz, exploratory correlation analyses were performed on all 5 blocks of the IGT with the other measures (BIS-11, IMT). After correction for multiple comparisons, this analysis revealed no statistically significant correlations. The relatively small size of the control group (N=20) may have contributed to the null findings. Future studies would benefit from larger control sample sizes.
Evaluation of substance abuse and pathological gambling via different measures of impulsivity, decision making, sensation seeking and time orientation revealed that substance abusing subjects did poorly on the IGT, but scores did not correlate with performance on impulsivity measures such as BIS-11 (Petry, 2001
). Comparisons of performance across the IGT, the Wisconsin Card Sorting Task (a measure of set-shifting), a delayed discounting procedure, and the BIS-11 revealed that higher impulsivity was associated with poorer performance on the IGT, but was not related to card sorting performance in nicotine dependent individuals. (Sweitzer et al., 2008
). In a college student sample, self-reported impulsivity and decision making on the IGT were examined. Only lack of premeditation was correlated with performance on the IGT (Zermatten et al., 2005
Limitations of this study include differences in education level in our cocaine dependent and control groups, noting that education was a covariate in the analyses. In regards to the difference in education between the groups, ANCOVA scoring was based on SCID-I education rating (1 = grade 6 or less, 2 = grade 7–12, 3 = high school graduate, 4 = education beyond high school). On further analysis, the level of education with most frequency in the cocaine dependent group was 3, or high school graduate (50%). For controls, it was 4, or partial college (35%). This signifies that even though there was some difference in level of education, education levels of completion were not highly discrepant (e.g., only a minority of cocaine-users or controls were college graduates). Importantly, this study used a control group closely matched in age and recruited from identical zip codes, thereby approximating a match to the cocaine dependent group in sociodemographics. Notably, IGT performance in the control group may appear inconsistent with performances of control subjects in prior studies (specifically, inconsistent performance across IGT blocks and a large standard deviation even in blocks 4 and 5). This may be due to our control group being recruited from the same zip codes as the cocaine-dependent group, and therefore more comparable in regards to socioeconomic status to our cocaine group than to control groups in previous studies comprised of middle-class adults or college students. Using multinomial logistic model, Fuentes et al. (2006)
distinguished pathological gamblers from controls with regression models that included both Go No-Go and BIS-11 scores. With larger datasets, similar approaches may be useful in future studies to examine combinations of factors (e.g., IGT EVM parameters, BIS-11 parameters, IMT outcomes) that may be revealing with regards to differences in cocaine dependent and control populations.
We found no significant correlation between EVM parameters of the IGT (meant to distinguish the underlying processes of decisions made on the IGT) with either measures of response inhibition and attention (IMT), or self-reports of impulsivity (BIS-11). One possible reason is that while similar, the IMT and IGT are measuring behavioral processes with unique features and sources of variance. Additionally, to more completely examine the relationship between decision-making, impulsivity, and behavioral inhibition, future studies might benefit from measures such as reflection impulsivity (the ability to gather information prior to making decisions) to further elucidate the processes of nonplanning and decision-making (Clark et al., 2006
). The concept of reversal learning, or the inability to terminate repetitive responses in the presence of previous learning or environmental cues may also play a role in decision-making (Fillmore and Rush, 2006
). One study found that in a population of polydrug users (cocaine and heavy alcohol use), subjects displayed acquisition of learning, but impaired discrimination-reversal learning of inhibitory and activational responses compared to controls (Fillmore and Rush, 2006
). It is possible that reinforcement contingencies may also play a role in the inability to reverse responses to stimuli in cocaine dependent subjects (Ersche et al., 2008
). Further examination of measures of decision-making with reversal learning in cocaine-dependent populations may be worthwhile to better elucidate cognitive deficits in this population.
According to (Barratt, 1993
), the best way to gather information about the clinical construct of impulsivity may be through the use of a battery of tasks with the overall information summed into an “impulsivity index.” More recently, the different cognitive processes measured for under the definition of “impulsivity” may be of importance in the treatment of substance abuse, and necessitate honing the definition of impulsivity, attention, and decision-making (de Wit, 2009
). The findings of the current study support this assertion. A battery of measures may provide the most comprehensive description of impulsivity and decision processes in a clinical population. These findings further support the hypothesis that the clinical construct of impulsivity is multi-factorial, and individual measures in isolation do not capture all its dimensions. The results also suggest that decision-making as measured by the IGT, though closely linked to impulsivity in clinical populations, may represent an independent - though likely not orthogonal - construct.