Conditioned emotional response after dorsohippocampal, ventrohippocampal or entorhinal cortical lesions in rats

Acquisition and extinction of the conditioned emotional response (CER) was studied in 24 male hooded rats which, prior to training, received small electrolytical lesions in the dorsal hippocampus, the ventral hippocampus, the entorhinal cortex, or were given sham operations. The rate of the on-going bar-pressing behavior for food pellets was highest in rats with lesions in the ventral hippocampus and the lowest after lesions in the entorhinal cortex. CER acquisition was markedly retarded and suppression was the weakest only in rats with dorsal hippocampal lesions. When compared with the level of suppression established toward the end of training, the greatest resistance to extinction of the CER was observed after entorhinal cortical lesions. The results of the experiment indicate functional heterogenity of the hippocampal formation.