Distinct substrates influence the acquisition of self-stimulation of the hippocampus and the prefrontal cortex

Self-stimulation (SS) of both the medial prefrontal cortex (MPFC) and the dorsolateral hippocampus (HPC) is known to develop slowly, over a period of days. In both cases, the acquisition of bar-pressing can be markedly hastened by delivery of noncontingent electrical stimulation for several days prior to SS training. The similarity of these effects suggests that there might be a common substrate mediating the acquisition process. However, in the present experiment, pre-training noncontingent electrical stimulation of the MPFC had no effect on how rapidly rats acquired the bar-pressing response for HPC stimulation, or vice versa. A further dissociation of the elements governing the acquisition process for these two SS sites was suggested by the observation that pre-training noncontingent stimulation of the entorhinal cortex facilitated the speed of acquisition of SS of the HPC but not of the MPFC. It seems that the HPC and entorhinal cortex can be excluded from the subset of neural structures which are known to influence the acquisition process governing MPFC SS. These and other data suggest that the development of SS of the MPFC and HPC can be regarded, at least in part, as involving a process rooted in distinct substrates.