Training of conditioned enhancement and conditioned suppression in rats

Stable conditioned enhancement of barpressing in rats was elicited by darkness stimulus signaling continuous food reinforcement (CRF) component of a multiple schedule in which 2.5 min variable interval reinforcement (VI) constituted the second component. Conditioned enhancement was rapidly acquired and resistant to extinction. In some groups concurrent alimentary and defensive training was conducted in which darkness signaled food CRF and acoustic white noise signaled inescapable foot shock, both presented against the 2.5 min VI food reinforcement schedule. The continuous reinforcement schedule and/or conditioned enhancement showed a decremental effect on conditioned suppression, but only when defensive trials were less frequent than trials with continuous reinforcement of barpresses. Residual enhancement of barpressing after termination of the stimulus eliciting conditioned enhancement, observed at early stages of training, was then changed to a slight decrease of the barpressing rate. Opposite changes were observed after the offset of the stimulus eliciting conditioned suppression. Changes in intertrial response rates are considered as reflecting the summation of stimuli possesing oposite motivational values.