Modulation of drug reinforcement by behavioral requirements following drug ingestion

Eight volunteers with histories of drug abuse participated in two experiments examining the modulation of drug choice by behavioral requirements following drug ingestion. Each morning subjects ingested colorcoded capsules containing triazolam (0.25 mg), d-amphetamine (15 mg), or placebo and then engaged in a relaxation or a computer vigilance activity. Experiment 1 involved two phases (i.e. a triazolam and a d-amphetamine phase), presented in counterbalanced order. Within each phase, subjects were first exposed to each of two compounds (placebo and either triazolam or d-amphetamine) once with each activity. Then every other day for 20 days subjects chose which compound they ingested with the vigilance and relaxation activities, with the restriction that they could not choose the same compound with both activities. Seven of eight subjects reliably chose d-amphetamine with the vigilance activity; all subjects always chose triazolam with the relaxation activity. In experiment 2 (5 days' duration), after re-exposure to the color-coded compounds used in experiment 1, subjects chose which compound (placebo, d-amphetamine or triazolam) they ingested with the vigilance activity, and on another occasion (in counterbalanced order), which they ingested with relaxation activity. Seven of eight subjects chose d-amphetamine with the vigilance activity; all subjects chose triazolam with the relaxation activity. The relaxation and vigilance activities modulated triazolam and d-amphetamine reinforcement, thereby demonstrating a new class of environmental variable that can influence drug self-administration.