Effects of alcohol on reinforced repetitions and reinforced variations in rats.

Six rats were rewarded with food pellets for repeating a particular sequence of four responses on two levers, namely left-left-right-right. Ethanol (0.75 g/kg and 2.0 g/kg injected IP) increased the variability of sequences under these "repeat" contingencies, resulting in fewer rewarded trials. Six other rats were rewarded only if their sequence of left and right responses in the current trial differed from each of the previous five trials. Ethanol had little effect on sequence variability and no effect on reward probability under these "vary" contingencies. The relative difficulties of the repeat and vary tasks were manipulated to show that task difficulty did not account for the results. Thus alcohol increased or maintained behavioral variability, thereby impairing reinforced repetitions but not reinforced variations. When previously reported results from rats in radial arm mazes were compared with a simulated random model, alcohol was found to increase behavioral variability under that procedure as well.