Determinants of the slow acquisition of medical and sulcal prefrontal cortex self-stimulation: an individual differences approach.

Stimulation-naive rats were tested for motor activity during noncontingent electrical stimulation of the medial prefrontal cortex (MPC) or sulcal prefrontal cortex (SPC). Defecation during stimulation was also measured. The rats were then tested using a conditioned taste aversion paradigm for aversion to a novel flavor (0.1% saccharin) paired with stimulation. Finally, the rats were trained to acquire self-stimulation over 26 days of training. Large individual differences were seen in motor activity, defecation, and conditioned taste aversion to initial stimulation and in the subsequent speed of self-stimulation acquisition. In the MPC-stimulated group, acquisition speed was positively correlated with motor activity to initial stimulation and negatively correlated with defecation to this stimulation. In the SPC-stimulated group, the same correlations were evident, but only when rats suffering seizures prior to self-stimulation acquisition were excluded from the analysis. Such preacquisition seizures, which were only found in the SPC-stimulated group, retarded self-stimulation acquisition. In most rats, MPC or SPC stimulation failed to condition a taste aversion to saccharin. These results suggest that the slow acquisition of MPC and SPC self-stimulation may be partly related to the motor suppressive, aversive, and convulsive properties of initial stimulation.