Positive and negative contrast effects with hypothalamic reward

Abstract

Rats trained to press a bar for hypothalamic reinforcement exhibited negative or positive contrast effects when current intensity was decreased or increased, respectively. Both contrast effects were large and persistent. The positive contrast effect was highest during the first 3 post shift min and lasted for approximately 8 min. Negative contrast was maximal during the second and third post shift min and lasted for the whole 15 min post shift period. The ease of obtaining positive incentive contrast with hypothalamic reward as compared with conventional reward is hypothesized to be due to two factors: the use of a shift in quality rather than quantity of reward and the use of low drive levels during testing.