Motivational effects of compounding discriminative stimuli associated with food and cocaine

In previous experiments, the compounding of two discriminative stimuli associated with the same reinforcer increased rats' responding approximately three-fold, regardless of whether the reinforcer was food, water, cocaine, or shock-avoidance. Compounding a discriminative stimulus associated with food with one associated with water increased responding two-fold. In the present experiment, compounding a discriminative stimulus associated with food with one associated with cocaine increased responding two-fold. These results support the hypothesis that 1) the effects of stimuli associated with reinforcers from the same incentive class (appetitive or aversive) are mutually enhancing, and 2) the combined effects of stimuli associated with two different reinforcers from within the same class are not as strong as those of two stimuli associated with the same reinforcer. These results also suggest that discriminative stimuli associated with non-drug reinforcers may increase the motivation to self-administer cocaine when encountered in combination with drug-related stimuli.