Scopolamine is a muscarinic cholinergic antagonist which impairs acquisition and retention performance in a variety of cognitive tests. The present study outlines two experiments exploring the effects of scopolamine on rat serial pattern learning. The first experiment compared acquisition of a perfect versus violation pattern in rats given either scopolamine or saline. Rats were given daily i.p. injections of either saline or scopolamine (0.6 mg/kg) and trained in an octagonal operant chamber equipped with a nose poke receptacle on each wall. They learned to make nose poke responses for water reinforcement in a discrete-trial procedure with correction. Rats were trained on one of two patterns composed of eight 3-element chunks:
Perfect: 123-234-345-456-567-678-781-812
Violation: 123-234-345-456-567-678-781-818
where the digits represent the clock-wise positions of receptacles in the chamber, dashes indicate 3-s pauses, and other intertrial intervals are 1 s. This experiment provided evidence as to how cholinergic systems are involved in rats’ abilities to learn serial patterns with or without a violation element. By comparing acquisition of these two types of patterns in the presence of scopolamine or saline, we were able to determine that the violation element did not interfere with the acquisition of the other elements of the pattern.
The second experiment presented a reversal learning task in which rats from Experiment 1 were transferred to an unphrased version of the pattern experienced in Experiment 1. Further, rats were transferred to either a same or different drug condition than what was experienced in Experiment 1 to allow for an examination of the effects of prior versus current drug state on rats’ abilities to learn the reversal learning task. It was revealed that scopolamine dissociated the two cognitive systems necessary for encoding and performing correctly at chunk boundary elements versus the violation element. Specifically, our evidence suggests that muscarinic cholinergic systems are more necessary for making correct responses at the chunk boundary elements than making correct responses at the violation element during cue removal.