Pavlovian influences over food and drug intake

Consuming food and taking drugs share several important characteristics. In particular, each causes changes in important physiological parameters that are constantly being monitored and regulated by the brain. As examples, bl ood glucose increases after meals; and body temperature decreases after eth anol is taken. Such changes elicit neurally-mediated homeostatic responses that serve to reduce the magnitude and duration of the perturbation. It is argued that when an individual can accurately anticipate pending meals or d rugs, it can make appropriate responses to minimize or totally neutralize t he meal/drug-elicited perturbations. This phenomenon, which is the basis fo r meal and drug tolerance, relies upon Pavlovian conditioning. Literature i s reviewed which documents the role of conditioning processes in the develo pment of tolerance. The argument is made that conditioned responses enable individuals to derive necessary or desirable aspects of food and drugs whil e minimizing some of their negative effects. In a final section, drug toler ance is discussed as a natural consequence of evolution-derived, meal-relat ed learning processes, with associated negative consequences. (C) 2000 Else vier Science B.V. All rights reserved.