The study tested the effects of sodium pentobarbital on rats' abilities to learn and remember certain taught responses. These rats were randomly assigned to one of two groups – substance administered or no substance administered (the control condition) – and then placed in a simple maze and taught to escape an electrical shock. Overton found that the rats that had been administered 25 mg of sodium pentobarbital could no longer remember the proper escape response when they were later placed in the maze without the drug.