Abraham Wikler (died 1981) was one of the first researchers who, in the late 1940s, strongly advocated the idea that drug abuse and relapse following treatment are influenced by basic learning processes. Early in his career, Wikler became interested in reports from relapsed heroin addicts that despite being free of withdrawal symptoms during treatment and upon discharge, they experienced withdrawal symptoms and craving when they returned to their drug-use environments—and that these feelings were responsible for their return to drug use.

Based on these and other anecdotes, Wikler—who was familiar with the recent work of Russian physiologist Ivan Petrovich Parlor (1849-1936) on conditioning—proposed that events which reliably signal drug self-administration or drug withdrawal elicit conditioned responses (CRs) that take the form of withdrawal and drug craving. According to Wikler, these CRs motivate...