Are schedule-induced drinking and displacement activities causally related?

The acquisition of schedule-induced drinking was studied in hungry rats given food according to an intermittent (fixed-time 45-s) schedule, in three separate experiments. Rate of acquisition of induced drinking was not affected by making the rats thirsty as well as hungry (Experiment I), nor by offering them a palatable saline solution instead of water (Experiment II). Thirst and palatability did affect the asymptotic level of induced drinking. Increasing the level of food deprivation (Experiment III) increased both the rate of acquisition of induced drinking and its asymptotic level. Thus, rate of acquisition of induced drinking was found to depend more on causal factors relevant to feeding than on causal factors relevant to drinking, while asymptotic level of drinking was affected by both types of causal factor. This suggests that the occurrence of induced drinking does not depend primarily on a disinhibition mechanism of the type thought to underlie displacement activities, and hence does not support the idea that induced drinking is a type of displacement activity.