Enhancement of bar-pressing rate in rats by the conditioned inhibitor of the CER.

The acquisition and stability of the conditioned inhibition of conditioned suppression (CER) was studied in two groups of 16 rats. The intensity of a white noise CS influenced the speed of CER acquisition and the amount of suppression. However, CS intensity exerted no effect on subsequent inhibitory training. During inhibitory training two kind of trials were presented: the CS paired with unavoidable shock and the same CS preceded and accompanied by the conditioned inhibitor (CI) consisting of offset of the house light. After only brief training the CS presented with the background of the CI lost nearly all suppressing properties, and concurently the suppressing effect of the CS paired with shock was markedly attenuated as well. At the end of training the CI typically enhanced on-going bar-pressing behavior. Some rats did not reach the required criterion of differential responding on the two kind of trials since the CS completely lost suppressing properties on regular CER trials. Differential responding of other rats was resistant to manipulations involved in frontal brain lesions. Reports of enhanced bar-pressing observed in number of CER studies were reviewed and discussed.