Effects of pentobarbital on punished behavior at different shock intensities.

Key-pecking by two pigeons was maintained initially under a schedule where the first response after five minutes had elapsed produced food. When every 50th response produced shock, responding was suppressed (punishment). Although rates and patterns of punished responding remained comparable when the shock intensity was reduced by half, pentobarbital produced much greater increases in both overall and local rates of responding at the lower shock intensity. Pentobarbital also produced larger increases in the low rates of responding immedicately following shock when the lower intensity shock was in effect.