Scopolamine-induced impairment of delayed recognition of abstract visual shapes

Since the limbic system, whose involvement in cognitive processes is well documented, constitutes a major central cholinergic area, the effect of cholinergic drugs on cognitive tasks has been studied extensively. In the present study, we used a long-term visual recognition task to evaluate the persistence of the scopolamine-induced anterograde amnesia beyond drug clearance intervals. Following memorization of a list of abstract shapes, subjects were evaluated on recognition performance immediately after encoding, and after a 3-day interval. Administration of scopolamine (0.4-0.8 mg) 70 min prior to encoding induced a significant (8-16%) deficit in delayed recognition performance. In contrast, a scopolamine challenge on delayed recognition following a drug-free encoding did not influence memory performance. In contrast, even at peak levels, scopolamine did not alter immediate recognition, detection or visual discriminative performances. Hence, the presence of scopolamine during the encoding of the shapes induced a significant long-term memory deficit that persisted after scopolamine clearance. Therefore, this paradigm is useful for imaging regional brain activation during impaired recognition without the confounding direct effects of scopolamine on cerebral blood flow or metabolism, two physiological variables underlying the indirect measurement of brain activation.