Temporal discounting in heroin-dependent patients: no sign effect, weaker magnitude effect, and the relationship with inhibitory control.

Impulsive behavior in heroin-dependent individuals and matched smokers was studied within the framework of temporal discounting. Two well-known effects were examined: the sign and magnitude effects (Kirby, 1997). The study also investigated the relationship between cognitive impulsivity and inhibitory control as measured by a Go/No-go task. Fifty-six heroin-dependent patients in the postmethadone treatment stage and an equal number of matched daily smokers participated in the study. The heroin-dependent patients showed higher discount rates in both gain and loss conditions. They also showed no sign effect by demonstrating similar discount rates in gains and losses. Heroin-dependent patients also exhibited a magnitude effect, which was weaker than that observed in smokers. Differential relationships between impulsivity and inhibitory control were found in the two groups. For smokers, decision-making and inhibitory control behaviors pertained to different psychological processes, whereas for heroin-dependent patients, the two behaviors were partially related. Finally, a significant correlation between length of heroin use and temporal discounting with small magnitude was found. The present study advances our understanding of the specific behavioral impulsive patterns in heroin-dependent individuals.