Schedule-induced wood-chewing in rats and its dependence on body weight

Abstract

In Experiment I, 12 rats were exposed to an FT 60 schedule of food reinforcement, followed either by extinction or by a massed-food control condition, in the presence of a wood block. In 9 rats, wood-chewing behavior increased systematically during the FT 60 condition and declined again during extinction or massed food, while the other 3 rats showed virtually no chewing behavior at any stage of the experiment. In Experiment 2, frequency and bout duration of wood-ehewing under an FT 60 schedule of food reinforcement declined as body weight increased, in 7 rats. We conclude that wood-chewing qualifies as a schedule-induced behavior, and that it resembles schedule-induced drinking in its dependence on body weight. Unlike drinking, however, induced chewing occupied the middle region of the 60-sec interreinforcement interval, declined markedly within the session, and showed considerable within-and between-subject variability. Falk (1961) found that when rats were allowed to obtain food according to an intermittent (VI 60-sec) schedule of food reinforcement, and were given concurrent free access to a water bottle, they developed the habit of drinking immediately after eating each food pellet. Because the rats' cumulative intake of water under these circumstances was abnormally large, Falk referred to the postpellet drinking as "schedule-induced polydipsia." Schedule-induced polydipsia has been extensively studied in the subsequent two decades, but its cause remains obscure: numerous explanations have been offered, but none has proved satisfactory (see reviews by Falk, 1971;Segal, 1972;Staddon, 1977).Explanations of schedule-induced drinking have been of two distinct types, which may be termed "thirst" explanations and "general activation" explanations, respectively (Roper, 1980b). "Thirst" explanations hold that intermittent presentation of food exerts a specific facilitatory effect on drinking, for example by stimulating oral dehydration receptors (Stein, 1964)or by causing a fall in blood glucose level (Freed, Zec, & Mendelson, 1977). "General activation" explanations, on the other hand, hold that intermittent presentation of food exerts a more or less general facilitatory effect on nonfeeding behaviors, via a state or process termed frustration (e.g., Thomka & Rosellini, 1975), arousal (e.g., Killeen, 1975; Brett & Levine, 1979), general motor excitability (Wayner, 1974), or stress (e.g., Wallace & Singer, 1976).At present most investigators seem to favor a gen- eral activation account, on the grounds that schedule induction extends across a variety of species, reinforcers, and behaviors. But whether one regards induction as a general phenomenon depends on the stringency of one's definition. The term "scheduleinduced" is commonly applied to any activity that occurs during interreinforcement intervals, regardless of its frequency of occurrence, whereas a stringent demonstration of induction requires that the behavior in question be shown to occur more frequently in association with a schedule of reinforcement than ...

Factors affecting schedule-induced wood-chewing in rats: Percentage and rate of reinforcement, and operant requirement

“…In this way, we hope to determine the extent to which SIP depends on special characteristics of the relationship between eating and drinking in the rat, as opposed to reflecting the operation of more general principles. We have recently confirmed that wood-chewing can occur as a schedule-induced behavior in rats when food is intermittently available, and have shown that induced wood-chewing (like SIP) is inversely related to level of food deprivation (Roper & Crossland, 1982). This finding supports the idea that schedule indueWe thank the SRC for financial support.…”

“…Pellet delivery was signaled by 2.S-sec illumination of a light above the food tray, as well as by the sound of the dispenser. During pretraining, no wood block or water spout was present, because experience had shown that prior adaptation to an FI 6O-sec schedule facilitated the subsequent appearance of induced wood-chewing (Roper & Crossland, 1982).…”

Adjunctive behavior of the rat under periodic food delivery in a 24-hour environment

“…These results thus support the conclusion of Roper and Nieto (1979) that severe deprivation is not necessary to induce adjunctive behavior. However, other work suggests that some responses, in particular, wood-chewing (Roper & Crossland, 1982), may show more robust changes under severe food deprivation. Such a trend for chewing was apparent in our data for 1 subject.…”

Response–food delay gradients for lever pressing and schedule-induced licking in rats

“…Schedule-induced drinking, on the contrary, does not show systematic relationships with variables related to drinking behavior itself, such as the animal's level of thirst or the nature of the liquid available (see Pellón, 1992). Although scheduleinduced polydipsia covaries more with food motivation than with water motivation, water may have ancillary reinforcing properties by making the food pellet itself more reinforcing (Keehn & Burton, 1978;Roper & Crossland, 1982).…”