Effects of d-amphetamine in human models of information processing and inhibitory control

Although stimulants are generally associated with enhanced information processing, reports of stimulant effects on behavioral functions that rely on inhibitory processes have been inconsistent. The present research tested the joint effects of d-amphetamine on information processing and inhibitory control in healthy adults (N = 22) with no reported history of illicit stimulant use or drug dependence. Information processing was measured by a rapid information processing (RIP) task and inhibitory control was measured using a stop-signal task. Performance was measured in response to 15 mg/70 kg, 7.5 mg/70 kg, and 0 mg/70 mg (placebo) doses of d-amphetamine, administered double-blind in a randomized, within-subjects design. Results showed that d-amphetamine improved information processing in a dose-dependent manner. By contrast, no enhancement of response inhibition was observed. Stimulant effects were also observed in physiological and subjective effects measures. The findings indicate that a stimulant drug can enhance aspects of cognitive functioning without producing a concomitant improvement in inhibitory control of behavior. The findings highlight the complex nature of stimulant effects on human behavior and the utility of performance tasks as models of complex behavioral and cognitive functions.