In humans, cocaine use has long been associated with poor attentional control and decreased efficiency in goal-oriented behavior. Animal models of these stereotypic drug effects, however, have thus far failed to produce quantifiable data sets in part because of a lack of species differences and analysis techniques. Recent work (Hervey et al. 2006) has successfully quantified attentional lapses in disorders such as ADHD through the analysis of response time variations in simple tasks, but this analysis has yet to be applied to the drug abuse scenario. To determine the effects of chronic cocaine administration on response time variability, 14 rhesus macaque monkeys (8 cocaine administering and 6 performance-matched controls) were subjected to a 50 trial simple attention task. This task was performed W-F prior to cocaine self-administration sessions in the test group. Treatment groups were compared to both each other and to baseline task sessions recorded prior to beginning the administration paradigm. In addition to typical measures of variability, an ex-Gaussian response time analysis was performed to quantify the contribution of attentional lapses to overall variability. The cocaine-administering group had a significantly higher response time standard deviation than their pre-administration sessions (p<0.05). No difference was observed between pre- and post-administration sessions for the control group. When ex-Gaussian methods were applied to the response time datasets, no differences were observed between groups in the normal mean (mu), suggesting that the variability increase in the cocaine group was due to an increased skew in the right tail of the response time distribution. Indeed, the cocaine group showed a significant increase in the value of tau(exponential value representing the distribution tail magnitude) post-administration versus tau pre-administration (p<0.05). These data suggest that cocaine administration leads to increased behavioral variability in simple response time tasks, and that this variability increase is primarily due to the prevalence of abnormally long responses. Similar results have been demonstrated in clinical disorders such as ADHD, suggesting both the relevance of the primate model in studies of attentional processing and the possible similarity in affected brain regions or transmitter systems
