John Davis and the meanings of licking

This paper reviews the contribution of John Davis to understanding how meal size is organized and controlled in the rat. By measuring the rate and pattern of licking of various liquid diets during sham feeding and real feeding, Davis demonstrated that meal size is the result of the central integration of positive feedback from orosensory stimulation and negative feedback from postingestive stimulation of the stomach and small intestine. The potency of these feedbacks is modulated by a variety of factors including experience and deprivation. At the microstructural level, orosensory stimulation increases burst size or cluster size, while postingestive negative feedback decreases the number of bursts or clusters. His results remind us that behavior is the basic science of ingestion, important in itself, and essential for the investigation of the neural mechanisms that organize it.