PROJECT SUMMARY The importance of complex learning, memory and verbal/symbolic processes in the development, maintenance and relapse of substance use disorders (SUDS) is increasingly being recognized. Drug-related cues and behaviors develop and alter in value based on direct association with drug experiences but are also determined by verbal and other symbolic processes. Research on these aspects of SUDS is hampered by the limited availability of animal models of such processes. The two PIs, Dr. Galizio and Dr. Bruce, have developed a model of symbolic processes in rats: classes of olfactory stimuli that are physically dissimilar but are related through a history of association. Twelve odors are arbitrarily partitioned into two sets of six. Rats are trained to make instrumental responses for reward to one set with no reward for the other until they are responding exclusively to the rewarded set. Then reward contingencies are repeatedly reversed and, after extensive training with these procedures, the animals begin to show transfer of responding or non-responding to all members of each set after exposure to just a few. This transfer of function among stimuli without direct exposure to the changed contingencies defines a functional equivalence class and the proposed research will explore whether these classes share key properties with human symbolic classes or categories. Aim 1 will test whether pairing of a novel stimulus with one class member will result in the novel stimulus coming to be related to all class members without explicit training. This is called class expansion and is readily demonstrated in humans. Aim 2 will test whether transfer of a novel instrumental response across class members will occur in rats as they do in humans. Aim 3 will test transfer of a Pavlovian conditioned response across class members assessed in a cue- induced reinstatement paradigm. Finally, in a proof of concept experiment, Aim 4 will examine whether an odor preference induced by pairing with morphine will transfer to other class members. These studies form the basis for a model of symbolic processes in rats with potential translational value to the treatment of SUDs.