Hippocampal stimulation limits performance but does not retard acquisition of food-reinforced learning

Facilitation of the usually very slow acquisition of hippocampal (HPC) self-stimulation (SS) by prior, non-contingent HPC stimulation may be due to the progressive attenuation of a disruptive effect of the stimulation on learning. We attempted to answer two questions: (1) Does HPC stimulation disrupt food-reinforced learning when it follows each lever-press as in SS experiments? (2) Does prior exposure to the stimulation attenuate any such disruptive effect? We observed no significant differences in the rate of acquisition when each food-reinforced response was paired contingently with a 0.5 sec train of dorsal HPC stimulation (CS group), or when 0.5 sec trains were administered randomly throughout the session (RS), compared with an implanted control group (IC). Although acquisition was rapid in all groups, performance on the second day was significantly lower in the CS group than in the IC animals. These same electrode placements later supported SS. The same results were obtained with 3 similarly-treated groups that had previously received a program of daily HPC stimulation (kindling). The results imply that kindling does not produce its facilitating effect on acquisition of HPC SS by removing a disruptive effect of the stimulation.