Schedule-induced drinking: entrainment by fixed- and random-interval schedule-controlled feeding.

Six underweight rats drank in a polydipsic pattern of single post-reinforcement bursts of licking before bar-pressing for subsequent food reinforcers scheduled at fixed 60-sec intervals. With a 60-sec random interval schedule they frequently oscillated between barpressing and drinking. On both schedules mean drink durations were shorter than average inter-reinforcement times, but longer drinks occurred under the fixed-interval schedule. We concluded that intermittent reinforcement entrains drinking because food plus water is more reinforcing than dry food alone, and that polydipsia develops when opportunities for drinking do not compete with opportunities for feeding.