Basic research on simple and complex (i.e., contextual effects) respondent conditioning has applied importance. Recently, the u.S. government has declared war on the import and use of illegal drugs. One result of this is that more money is being spent on research to identify the factors that affect drug use and abuse. Several experiments have shown that conditioned stimuli can produce drug-like effects in both humans and other animals, disrupting behavior and producing physiological changes. In addition, stimuli that have been paired with drugs sometimes produce internal conditioned responses that are opposite to the unconditioned effects of the drug. For example, when animals are injected with insulin (US), the unconditioned response is a reduction in blood sugar (UR). The response to a stimulus (CS) that has been paired with insulin is exactly the opposite; blood sugar levels increase (Siegel, 1972, 1975).
Similar counteractive effects have been found with drugs other than insulin. For example, amphetamine reduces appetite, but a CS that has been paired with it increases food intake (Poulos, Wilkinson, & Cappell, 1981). Pentobarbital is a sedative, but the response to a conditioned stimulus associated with pentobarbital counteracts the drowsiness ordinarily associated with the drug (Hinson, Poulos, & Cappell, 1982).
Effects such as these suggest that respondent conditioning plays a major role in drug tolerance. Here is how it works. With repeated pairings of a drug (US) and a CS (e.g., injection process), the conditioned response gains in strength and increasingly opposes the unconditioned effects of the drug. This means it will take larger and larger amounts for the user to experience the same degree of effect. In everyday life, conditioned stimuli arise from the time of day that a drug is taken, the way it is administered (e.g., using a needle), the location such as a tavern or home, and social events like a party or dance.
Notice that, in the case of tolerance, the reduction in the effects of the drugs (UR) is not due to habituation; rather it is the result of the counteractive effects (CR) to the injection process and setting (CS). When more of a drug (US) is needed to obtain the same drug effects (UR), we talk about drug tolerance (Baker & Tiffany, 1985). Thus, the counteractive effects to CSs are major components of drug tolerance.
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