Humans abusing psychoactive drugs report characteristic subjective effects, and drug discrimination procedures in rats and monkeys are extensively used to model these effects. The organism’s ability to perceive and identify the characteristic interoceptive effects of drugs is thought to play a role in drug-seeking, encouraging the development of this behavior and directing it towards one substance rather than another, on the basis of relative potencies and effects (46). To assess the discriminative effects of drugs, animals are trained with response-contingent food-pellet delivery or stimulus-shock termination to respond on one lever after an injection of a training dose of a drug and on the other lever after an injection of vehicle. Once animals learn to reliably make this discrimination, the subjective effects of different drugs can be compared and the modulation of subjective effects of drugs of abuse by various pharmacological ligands can be studied.
