Conditioned taste aversion and drugs of abuse: history and interpretation

Conditioned taste aversion (CTA) learning describes a phenomenon wherein an animal learns to avoid consumption of a particular taste or food following its pairing with an aversive stimulus. Although initially demonstrated with radiation and classical emetics, CTAs have also been shown with drugs of abuse. The ability of rewarding drugs to support CTA learning was described as paradoxical by many investigators, and a number of attempts have been made to resolve this paradox. The present review offers a historical perspective on the CTA literature with a particular focus on CTAs induced by self-administered drugs. Specifically, this review describes and summarizes several interpretations of CTA learning that offer possible mechanisms by which drugs of abuse support CTAs, including sickness, drug novelty, reward comparison and conditioned fear. It is concluded that the reported "paradox" is no paradox at all in that drugs of abuse are complex pharmacological compounds that produce multiple stimulus effects, not all of which are positive reinforcing. Finally, a possible role of drug aversion in drug self-administration is discussed.