Effects of repeated alcohol administration on human operant behaviour

Nine human subjects were exposed to a multiple fixed-ratio (FR) differential-reinforcement-of-low-rate (DRL) schedule of monetary reinforcement. Presses on a manipulandum requiring relatively high force were occasionally followed by an increased money total displayed on a computer screen. Subjects were exposed to the schedule until their behaviour had stabilized. Prior to each of the next three sessions they were administered 0.85 g/kg alcohol. In eight of the nine subjects the initial effect of alcohol was to increase FR response rate and, consequently, reinforcement rate. Subsequent alcohol administration resulted in sensitization: even greater rate-increasing effects. In two further control sessions behaviour returned towards baseline level. DRL response rate was slightly increased by alcohol, but reinforcement rate remained unchanged. There was no consistent change in DRL response or reinforcement rates from the first to the third alcohol sessions. The effects of alcohol on human behaviour were similar to the effects found in studies with animals. The results were also consistent with the view that the changes in behaviour which occur with repeated drug administration depend in part on whether the initial effect of the drug is to increase, decrease or produce no change in reinforcement rate.