Effects of d-amphetamine on behavioral control in stimulant abusers: the role of prepotent response tendencies

The present study examined the effects of d-amphetamine on the ability to execute and inhibit behavior in a context where preliminary information signaled the likelihood that a response should be executed or suppressed. Eight adults (5 men and 3 women) with a history of stimulant abuse performed a cued go no-go task that required quick responses to go targets and suppression of responses to no-go targets. Performance was tested under four oral doses of d-amphetamine, 0 (placebo), 5, 10 and 20 mg, administered double-blind and in mixed order. d-Amphetamine produced a dose-dependent increase in inhibitory failures following invalid go cues and had no effect on inhibitory failures following valid no-go cues. d-Amphetamine had little effect on response execution as measured by reaction time. Subjective and physiological effects of d-amphetamine were also observed. The findings demonstrate that stimulant effects on fundamental aspects of behavioral control can be mediated by environmental cues that alter response tendencies. Identification of environmental conditions in which stimulants are likely to disinhibit behavior could provide insight into mechanisms that underlie the association between long-term stimulant use and poor impulse control.