Journal of Comparative and Physiological Psychology 1966, Vol. 61, No. 1, 1-4 NOVEL FOOD PREFERENCES IN THIAMINE-DEFICIENT RATS 1 WILLARD RODGERS ANDPAUL ROZIN University of Pennsylvania Thiamine-deficient rats choosing between a novel diet and a familiar diet in- variably showed a marked preference for the novel diet. If the novel diet con- tained thiamine, this preference was maintained over a 10-day period. If the novel diet was deficient in thiamine, and thiamine was added to the familiar diet, Ss switched from an initial novel diet preference to a familiar diet pref- erence after 3-4 days. Control rats showed no preferences for either diet. The exclusive initial ingestion of a novel diet may facilitate the development of a sustained, learned preference. That thiamine (vitamin Bl) deficient rats prefer foods containing thiamine has been known for years, but very little is known about the mechanism of the preference. Some of Richter's work (e.g., Richter, Holt, & Barelare, 1937) suggests that many pref- erences based on dietary deficiencies may in- volve innate recognition of the needed com- ponent. One difficulty with this explanation is the failure of an immediate response to thiamine to appear reliably in deficient rats. Furthermore, if thiamine is initially paired with a distinctive flavor and after- wards switched to a diet with a different flavor, thiamine-deficient rats continue to prefer the diet with which the thiamine was originally associated (Harris, Clay, Har- greaves, & Ward, 1933; Scott & Verney, 1947). Most investigators believe that thiamine preference is learned: ingestion of thia- mine-rich foods makes the thiamine-de- ficient rat feel better. This explanation of thiamine hunger by a simple reinforcement mechanism also runs into a number of dif- ficulties, (a) Ingestion of thiamine would not have any beneficial effects for at least 10 min., and probably not for 30 min., and learning does not ordinarily take place with such a long delay of reinforcement. Fur- thermore, a normal rat in a preference- testing situation frequently samples from the dietary choices available. Unless there is a mechanism operative in the deficient rat which results in an exclusive choice of the thiamine-containing diet, thiamine's beneficial effects would not be associated 1 This research was supported by National Sci- ence Foundation Grant GB-1489. * with eating that particular diet. (6) Thi- amine-deficient rats injected with large quantities of thiamine from 12 hr. to 10 days before being offered a choice between a deficient and a thiamine-containing diet nevertheless show a strong preference for the thiamine diet, even though the thiamine ingested orally presumably has no effect (Rozin, 1965). (c) No preference is ob- served when thiamine is in one of two bot- tles of water, in spite of the fact that thiamine produces the same physiological effects in the rat whether ingested in water or food (Rozin, Wells, & Mayer, 1964). The situation, therefore, remains unclear, insofar as the explanations of thiamine preference (as innate and as learned) seem equally inadequate. It may be, however, that while neither explanation is correct in itself, there is some truth in each. Perhaps there is an instinctive feeding pattern in the thiamine-deficient rat which maximizes the possibility of learning. An analogous explanation has been offered for the reac- tion of wild rats to poisoned foods (Rzoska, 1953). Rats that have been poisoned some- times develop a reluctance to eat new foods. When they finally try a new food, they frequently take only a few nibbles and then leave the food for a period of time before eating more. This sampling method would apparently maximize the possibility of associating ill effects with a particular food. It is possible that a similar, but re- versed, response to new foods is present in the thiamine-deficient rat. Our casual ob- servations indicated that these rats re- sponded readily to novel foods, and sug- gested the experiment that is reported here.