LEARNING AND HOMEOSTASIS - DRUG-ADDICTION AND THE MCCOLLOUGH EFFECT

The contribution of conditioned responses (CRs) to homeostasis may be seen by examining seemingly disparate phenomena of color vision (after effects and chromatic adaptation) and drug addiction (withdrawal sympt oms and tolerance). Color aftereffects may be elicited by nonchromatic stimuli previously paired with color (the McCollough effect, [ME]). S imilarly, pharmacological aftereffects may be elicited by nonpharmacol ogical stimuli previously paired with a drug (withdrawal symptoms). Th e authors summarize evidence indicating that both the ME and withdrawa l symptoms are CRs. The chromatic CR is expressed as chromatic adaptat ion in the presence of color, and the ME in the absence of color. The pharmacological CR is expressed as pharmacological adaptation (toleran ce) in the presence of the drug, and withdrawal symptoms in the absenc e of the drug. Both drug withdrawal symptoms and the ME are manifestat ions of the contribution of conditioning to normal homeostatic regulat ion. The authors discuss the implications of this conclusion for under standing regulatory processes and the evolution of behavioral mechanis ms.