To our knowledge, this is the first study to investigate specifically the effects of antisociality and extent of multidrug use on indices of impulsivity among SDIs. The study revealed three important findings. First and foremost, contrary to predictions, we found that antisociality was associated with more advantageous decision-making performance on the IGT and thus with better cognitive impulse control, independent of extent of multidrug use. Second, there was indication of a significant improvement in decision-making performance across IGT trial blocks for the low multidrug use but not for the high multidrug use group, evidenced by a flatter learning curve in the high multidrug use group. Finally, greater extent of multidrug use was associated with general psychomotor slowing, but not with motor impulsivity per se on the Stroop.
In light of our earlier finding that psychopathic heroin addicts evidence impaired performance on the IGT (Vassileva et al., 2007
), current results suggest that impaired performance of antisocial individuals on the IGT may become evident only at the extreme end of the antisocial spectrum, when antisociality is a clinically diagnosable syndrome such as Antisocial Personality Disorder or Psychopathy, and not when it is manifested as a personality trait considered to be on a continuum with normality, such as degree of socialization as assessed by the CPI-So. One might thus speculate that a sub-clinical, “non-malignant” form of antisociality might exert a paradoxically facilitating effect on decision-making and cognitive impulsivity in SDIs. This will have to be investigated further by in future studies. Also, the fact that antisociality had no effect on motor impulsivity indexed by the Stroop task, but in contrast had a facilitating effect on decision-making/cognitive impulsivity may be related to better impulse control in the antisocial group particularly when rewards are involved.
With regards to our second finding, the flatter learning curve of the high multidrug use SDIs suggests that they do not learn the task contingencies and show greater tendency to perseverate on making decisions that were initially rewarding, but ultimately disadvantageous. Relative to the high multidrug use SDIs, our low multidrug use group was guided initially to a greater degree by the higher magnitude of the immediate rewards. Yet, they learned to shift their strategy as soon as the first punishment trials were delivered. In contrast, the high multidrug use subjects continued to be guided by the prospect of immediate short-term gains, and never changed their selection strategy throughout the task.
Finally, the significance of the overall slowing in the high multidrug use group on the Stroop Task remains unclear, because additional analyses revealed that differences in Stroop reaction times were found to be accounted for by Hepatitis C serostatus. This is consistent with a recent report from our laboratory (Martin et al., 2004
) indicating that a positive Hepatitis C serostatus is associated with overall slower information processing on the Stroop task, and deserves further investigation.