Improvement of memory for classically condition associations by post-training self-stimulation

The effect of post-training self-stimulation on associations formed during classical conditioning was studied. In the first three experiments, rats experienced tone-shock, tone-water and tone-light pairings, respectively. Control groups experienced the same situations except that the temporal relationship between the stimuli excluded the possibility of an association being formed. Following this training period, the experimental animals pressed a bar for electrical self-stimulation of the brain; control animals did not self-stimulate. Retention of the association between the training stimuli was evaluated by measuring conditioned suppression of drinking (experiments 1 and 3), or extinction of secondary reinforcement. The results showed that self-stimulation can retroactively and non-contingently improve memory for associations in various classical conditioning situations, independently of the presence of a natural reinforcer or of the responses they elicit. In another experiment, the effects of varying amounts of tone preexposure (latent inhibition) and of varying amounts of post-training self-stimulation on retention of a tone-shock association, measured by the amount of tone-induced suppression of drinking, were studied. Increasing amounts of tone pre-exposure produced decreased retention over all levels of self-stimulation, and increasing amounts of self-stimulation produced increased retention over all levels of pre-exposure. The interaction of these two factors suggests that they both acted on the strength of the tone-shock association: the pre-exposure acted proactively to weaken the association; the self-stimulation acted retroactively to strengthen it. The effect of delaying the post-training stimulation for various times after the tone-shock pairings was also investigated. Retention was improved by self-stimulation delayed for 15 or 30 minutes, but was not affected by self-stimulation delayed for an hour. These experiments suggest that direct activatio