Background stimuli as a reminder after spontaneous forgetting: Potentiation by stimulation of the mesencephalic reticular formation

Reliable forgetting of a relatively complex maze is seen in rats when the training-to-test interval is 24 days. Forgetting is measured by longer time to run the maze and by an increase in the number of errors from the last training trials to the test trial. A contextual cue reminder alleviates forgetting when presented just prior to the test trial, but is only marginally effective when given 1 h before testing. The present experiment, using the same forgetting paradigm, was aimed at testing the hypothesis that such a marginal cuing effect can be potentiated by a stimulation of the mesencephalic reticular formation. Half of the animals were exposed for 90 sec to the experimental room (reminder condition), whereas the other half were exposed to the colony room (pseudoreminder condition), 1 h before testing. These two groups were divided into two subgroups, stimulated and pseudostimulated. The results showed that there was no effect of reminder alone and no effect of the stimulation given with the pseudoreminder; the stimulation given concurrently with the reminder alleviated forgetting as measured by errors. The results suggest that the stimulation acts to potentiate retrieval processes already triggered by the significant contextual cue reminder.