Studies of food preference, appetite and dietary habit. I. Running activity and dietary habit of the rat in relation to food preference.

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Abstract
Previous expts. revealed that pre-feeding (i.e., allowing animals to eat for a period of time immediately prior to being set to a task having food as an incentive) on sugar reversed their preference of sugar to powdered wheat, but the reversal was gradual. An expt. was indicated to decide between a chemical hypothesis and a conditioning hypothesis to account for the fact and nature of this reversal. Two groups of animals (8 [male][male] and 7 [female][female] in each group) were trained to shuttle back and forth between the test-food (sugar for one group and wheat powder for the other) and the starting box. Training periods were on alternate days, although the animals were fed Purina dog chow every day. After 12 practice trials, the [male][male] were pre-fed on the food with which they were trained. Six test-trials (on alternate days) were given with 5 min. pre-feeding and 3 with 15 min. pre-feeding. The [female][female] were given equal intervals of post-feeding on the food with which they were trained, to insure that the effects observed in the [male][male] were not due to general dietary conditions. Finally, both groups of animals were run on preference tests, which they were per- mitted to select sugar or wheat powder after being pre-fed on the food on which they had been trained; the [female][female] were still post-fed as controls. It is reasoned that, "if pre-feeding upon a particular food reduced the degree of partial hunger for that food, the pre-fed groups should prefer the opposite food, i.e., the wheat-incentive rats should prefer sugar to wheat, and the sugar-incentive rats should prefer wheat to sugar"; further, "if one assumes that the repeated in-gestion of a food produces an internal chemical adaptation which is a factor determining preference, then the post-fed and pre-fed rats should agree (at least to a certain extent) in their food selections. . . . If, on the other hand, one assumes that the repeated ingestion of a food by hungry rats conditions the animals to the acceptance of that food, then the post-fed rats should prefer the food to which they had been conditioned. . . ." Pre-fed animals in general, do prefer the opposite food; the preferences of pre-and post-fed animals in general do not agree, but under certain circumstances they may; and post-fed animals in general continue to prefer the food on which they have been trained. The author concludes that "at least three kinds of factors are required to explain the results ... (1) There is the reduction of a partial hunger through the technique of controlled pre-feeding. (2) There is conditioning which favors the selection of the food upon which the rat has been trained. (3) There is the general state of the organism[long dash]both chemical and neural[long dash]apart from the first two factors." It is noted that, "If a food preference has been established through pre-feeding, the cessation of pre-feeding results in a trend away from that preference and toward the reverse preference." The principle (previously observed by W. A. Bousfield) is verified that: "When rats are satiated upon one food they will not work (run) to continue eating it, but if another food is available, they may work with moderate and increasing activity to obtain that other food.".

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