Scopolamine infused into perirhinal cortex improves object recognition memory by blocking the acquisition of interfering object information

In a previous study, we reported apparently paradoxical facilitation of object recognition memory following infusions of the cholinergic muscarinic receptor antagonist scopolamine into the perirhinal cortex (PRh) of rats. We attributed these effects to the blockade by scopolamine of the acquisition of interfering information. The present study tested this possibility directly by modifying the spontaneous object recognition memory task to allow the presentation of a potentially interfering object either before the sample phase or in the retention delay between the sample and choice phases. Presentation of an object between the sample and choice phases disrupted subsequent recognition of the sample object (retroactive interference), and intra-PRh infusions of scopolamine prior to the presentation of the irrelevant object prevented this retroactive interference effect. Moreover, presentation of an irrelevant object prior to the sample phase interfered proactively with sample object recognition, and intra-PRh infusions of scopolamine prior to the presentation of the pre-sample object prevented this proactive interference effect. These results suggest that blocking muscarinic cholinergic receptors in PRh can disrupt the acquisition of potentially interfering object information, thereby facilitating object recognition memory. This finding provides further, strong evidence that acetylcholine is important for the acquisition of object information in PRh.