PII S0031-9384(98)00090 – 0 Motivational Conflict Among Water Need, Palatability, and Cold Discomfort in Rats MARTA BALASKO 1 AND MICHEL CABANAC 2 Department of Physiology, Faculty of Medicine, Laval University, Que ´bec, QC, G1K 7P4 Canada Received 30 June 1997; Accepted 5 March 1998 BALASKO, M. AND M. CABANAC. Motivational conflict among water need, palatability, and cold discomfort in rats. PHYSIOL BEHAV 65(1) 35– 41, 1998.—Rats were placed in situations pitting three motivations against each other. Two motivations, ambient temperature and need of water, were physiological drives. The third, water sweetness provided by sodium saccharin, was not considered as immediately physiological because saccharin does not provide physiological benefits for the animals; nevertheless they continued to seek the sweet taste after repeated exposure to it. Therefore, our aim was to explore whether these motivations are of the same nature for rats and, if they are, whether they are also quantitatively comparable. From the behavioral evidence we wanted to obtain information on the common currency that permits the rats to solve conflicts. Our results confirm the existence of a common currency in rats’ motivations. The similarity of rats’ behavior to that of humans observed in conflict situations, where maximizing the bidimensional sum of pleasure was the key to optimal behavior, allows us to suggest a role for affectivity in decision making of mammals. © 1998 Elsevier Science Inc. Decision making Cold Taste Conflict of motivations IT HAS been recognized by McFarland and Sibly (29) that behav- ior is the final common path for all motivations. Such a statement implies that a common currency exists for the ranking of priorities among conflicting motivations of widely different origins, as most behaviors do not permit the expression of other behavioral options at the same time (28,30). Some motivations are strictly mental (in no way connected to the maintenance of homeostasis), such as moral, religious, or ludic. Because these motivations can and must compete with, and possibly override, those connected to immedi- ate survival, the common currency to be common must be a mental signal. In humans, the affective dimension of consciousness has sev- eral attributes that suggest a possible role as the common currency in the process of decision making (6,7). Positive affective sensa- tion is connected to the correction of deviation from physiological order (4). A stimulus is thus perceived and reported to be pleasant when it contributes to the optimal equilibrium of some physiolog- ical value, like core temperature (1,2,11) or blood glucose level (3,18,40), and the same stimulus is reported to be indifferent or unpleasant when the optimal value of the milieu interior is reached or is overshot. This phenomenon of alliesthesia, which was de- scribed first by Aristotle in the case of taste, is a universal sensory experience. When several physiological functions are pitted against one another, a similar process takes place. Human subjects confronted by situations providing conflicting motivations seemed consistently to make choices that maximized their bidimensional sum of pleasure (6). Because animals also make decisions, a mental common cur- rency should exist as soon as thinking emerges in phylogeny. It is of interest, therefore, to test the theory in animals. However, as widely recognized by animal ethologists (15), in such studies the main and perhaps insurmountable problem consists in exploring experience and cognition in animals when the only evidence is behavioral. Incidentally, the problem is the same with human subjects. Any evidence we have that others, too, think, is behav- ioral, including verbal behavior. Among many others Rachlin showed clearly that mammals facing conflicting drives optimize their behavior (34,35). Rats were observed by Johnson and Cabanac (25) to have larger, less frequent meals to limit the exposure to a cold environment and to keep their food intake stable at the same time when food was provided at the distant end of a potentially lethal, cold alley. Collier and his coworkers studied the feeding and drinking behav- iors of rats in Skinner-box situations. They found that rats tended to maximize their foraging time efficiency more consistently than to minimize the cost/benefit ratio (12–14,22–24,27). These studies describe the behavior chosen by animals in conflict situations. The quantitative analysis showed that this be- havior was optimal, from the experimenter’s point of view, i.e., in terms of energy balance. However, they do not explain the prox- imal mechanism by which the decisions were made. In animals, the existence and the importance of affectivity and pleasure in this process may be indirectly inferred. Cabanac and Johnson (9) observed that rats regularly left their thermoneutral refuge, where standard food and plain water were provided, and ventured repeat- edly into a potentially lethal cold alley for the sake of obtaining 1 On leave from: Department of Pathophysiology, University Medical School, Pe ´cs, Hungary 2 To whom requests for reprints should be addressed. E-mail: michel.cabanac@phs.ulaval.ca Physiology & Behavior, Vol. 65, No. 1, pp. 35– 41, 1998 © 1998 Elsevier Science Inc. All rights reserved. Printed in the U.S.A. 0031-9384/98 $19.00 + .00 35