Scopolamine induced learning failures in man.

Two experiments were performed to determine the locus of the amnestic effects of scopolamine in man. The first experiment involved 24 volunteers receiving one of three doses of scopolamine (5, 8 or 10 microng/kg) or a placebo, intravenously. The subjects were tested for retention of material learned prior to administration of the drug, acquisition of new information, and retention of material learned while under the influence of the drug. Results indicated that scopolamine has its primary effect on the acquisition of new material and less of an effect on the retrieval of information already learned. The second experiment was designed to refine and expand upon the results of the first and involved 18 volunteers receiving eith 5 or 10 microng/kg of scopolamine or a placebo, intravenously. The subjects were given four trials to learn a list of verbal materials, and their recall for that material was measured at various intervals up to 24 h. These results confirmed those of the first experiment in that the predominant influence of the drug was to impair the acquisition of new information. Implications of these results for memory mechanisms are discussed.