DIFFERENTIAL ACTIVATION OF THE RAT HIPPOCAMPUS AND PERIRHINAL CORTEX BY NOVEL VISUAL-STIMULI AND A NOVEL ENVIRONMENT

Two groups of rats were shown individual novel visual objects. One gro up had been familiarised to the environmental context within which the objects were shown, the other experienced the situation for the first time. The activation of neurones in perirhinal cortex and the hippoca mpal formation was determined by counts of nuclei stained for products of the immediate early gene c-fos. The ratio of counts in the hippoca mpal formation to that in perirhinal cortex was compared for the two g roups: the ratio was significantly higher (4.2:1) in the group experie ncing the environment for the first time. Thus, whereas perirhinal neu rones are activated by novel rather than familiar objects, hippocampal neurones are preferentially activated by a novel rather than a famili ar environment. (C) 1997 Elsevier Science Ireland Ltd.