Dopamine and the mechanisms of cognition: Part II. D-amphetamine effects in human subjects performing a selective attention task

Background: A neural network computer model described in a companion paper predicted the effects of increased dopamine transmission on selective attention under two different hypotheses. Methods: To evaluate these predictions we conducted an empirical study in human subjects of D- amphetamine effects on performance of the Eriksen response competition task. Ten healthy volunteers were tested before and after placebo or D-amphetamine in a double-blind crossover design. Results: D-amphetamine induced a speeding of reaction time overall and an improvement of accuracy at fast reaction times but only in the task condition requiring selective attention. Conclusions: This pattern of results conforms to the prediction of the model under the hypothesis that D-amphetamine primarily affects dopamine transmission in cognitive rather than motor networks. This suggests that the principles embodied in parallel distributed processing models of task performance may be sufficient to predict and explain specific behavioral effects of some drug actions in the central nervous system.