Effects of chronic phenobarbital administration on forgetting functions in pigeons

The present study examined the effect of chronic phenobarbital administration on forgetting functions based on delayed matching-to-sample performance in pigeons. The effects of IP injections of 10 and 20 mg/kg administered over five consecutive training sessions were compared to each other and a baseline (no drug) condition. Percent correct was reduced as a function of both increasing delay and dose of phenobarbital. A quantitative analysis using a negative-exponential function fitted to bias-free measures of discriminability demonstrated that impaired performance following administration of phenobarbital was reflected in both an increase in the rate of forgetting as well as a decrease in initial discriminability. Furthermore, the influence of proactive interference arising from stimuli on previous trials was attenuated at the highest dose level (20 mg/kg). Thus, chronic phenobarbital administration impairs memorial function and limits the influence of information gained from previous trials on subsequent performance. The current effects of chronic phenobarbital administration are consistent with the effects of acute administration on forgetting functions reported in prior studies.