Motivation is a state that can be defined as a “tendency of the whole animal to produce organized activity” (Hebb, 1972), and such motivational states are not constant but rather vary over time. Early work by Wikler stressed the role of changes in drive states associated with dependence. Subjects described withdrawal changes as a “hunger” or primary need and the effects of morphine on such a state as “satiation” or gratification of the primary need (Wikler, 1952). Although Wikler argued that positive reinforcement was retained even in heavily dependent subjects (thrill of the intravenous opioid injection), dependence produced a new source of gratification, that of negative reinforcement (see above).
