Animal Models of Human Misbehavior
Modeling Misbehavior in theAnimal Laboratory
How can we recreate in the animal laboratory the conditions leading to the previously discussed maladaptive behavior? We can use a conditioned taste aversion preparation, in which rats come to avoid the intake of a taste due to its pairing with gastrointestinal illness (Garcia, Kimeldorf, & Koelling,1955; Garcia & Koelling, 1966). In this procedure, aversive conditioning is typically induced through the administration of an emetic (for example, an intraperitoneal injection of lithium chloride or, in some studies,exposure to X-rays) after the consumption of a flavored solution,such as salty water. So, in reality the solution is tasty and completely harmless, but it becomes aversive(yucky) and thereby avoided based on its pairing with illness. It is as if the rats “deduced” that their stomach pain was necessarily caused by something they ate. 1 Thus, the conditioned taste aversion preparation provides a good setting to recreate and, hence, study in the laboratory the processes involved in the learning and expression of food illness relationships (i.e., the C-E link).But, what about the relationship between the medicine and the noxious effect (i.e., the M-E link)? How can we model in the animal laboratory the impact of, say, the intake of antacid tablets on consumption of the tasty, yet potentially harmful food? Based on the discussion of our previous section, all we presumably need is to establish an inhibitory relationship between a second taste and illness or, in other words, a relationship in which a taste signals the nonoccurrence of illness.
This inhibitory relationship can be established in several ways, following different experimental procedures. Onesuch treatment consists of presenting a distinct taste (e.g., citric acid) while the animal is recovering from illness. That is, instead of giving the animal a taste immediately followed by the injection of the emetic, the emetic is given first,followed by the delayed presentation of the taste. This way, the taste is consumed while the animal is recovering from the noxious effects of the previously injected emetic. As a consequence of this treatment,consumption of this taste increases,presumably because the animal learns that it causes relief from illness or, in other words, that it produces a“medicine effect” (e.g., Barker &Weaver, 1991; Hasegawa, 1981;Zahorik & Bean, 1975; also see Garcia,Ervin, Yorke, & Koelling, 1967; Green& Garcia, 1971).
As interesting as all this is on its own,we must remember that our research attempts to study, in the animal laboratory, the excessive or reckless consumption of potentially harmful foods that can be induced by the previous intake of a medicine. In terms of a conditioned taste aversion preparation with rats, this can be translated as studying if the presence of the taste previously trained as an inhibitor for illness (i.e., the surrogate medicine) enhances the consumption of the taste previously paired with illness(i.e., the surrogate food).
Preliminary experimental data seem to meet our expectations: It might be possible to study the previously discussed human feeding misbehavior using rats in a conditioned taste aversion preparation. In a recently conducted study, three groups of rats (i.e., NoMed,Med, and NoAversion) first received a“medicine effect” treatment consisting of several trials on which a solution(citric acid) was presented 75 min after an injection of lithium chloride (i.e., the citric acid solution was presented during recovery from illness caused by the emetic). In a subsequent phase, GroupsNoMed and Med were given aversive conditioning with the salt solution, consisting of one pairing of this solution with the injection of lithium chloride,whereas Group NoAversion was given an unpaired presentation of the salt solution and the lithium chloride injection. At test, all groups were given 5-min access to the salt solution.Importantly, the salt solution was preceded by a 5-min presentation of the citric acid solution for Group Med, and of water for Groups NoMed andNoAversion (i.e., with volumes yoked to the consumptions of subjects in GroupMed). As can be appreciated in Figure 2, Group NoMed drank less of the salt solution than Group NoAversion on both test days, a result indicative of conditioned aversion to the salt solution in Group NoMed. The critical results are those of Group Med, which show that this group drank more of the salt solution than Group NoMed on both test days (although this difference was only statistically significant on the second test day). Because the only difference between the rats in Groups Med and NoMed lies in their having received citric acid or water, respectively, prior to being given the salt solution, we can deduce that the presence of citric acid, a taste that was previously learned to have a “medicine effect” (recovery from illness), was responsible for the enhanced consumption of the salt solution in Group Med. One can see the parallel between Mr. X's use of antacid tablets to indulge himself in tom yum and my Wistar rats drinking citric acid(a taste they actually dislike) in order to be able to safely enjoy their salty water.
A Nonconcluding Comment
It is at this point that caution is recommended to the reader. Even though it would be great to end this article with a clear take-home message,the truth is that there are more questions than answers on my desk right now. As a matter of fact, the previously discussed experiment (some additional results of the experiment that, for the sake of clarity, were not exposed here) and a study in progress have opened new questions that need to be answered. Thus, even when it is tempting to think that we have already found a procedure with rats to effectively model this human misbehavior we call reckless consumption of potentially harmful foods caused by medicine-induced safety, it is more appropriate to view these results as our first baby step.
Thus far, we have a promising, yet embryonic, idea in need of much nourishment and, hence, it would be irresponsible to make a claim based on such idea. As Carl Sagan (1987) replied when he was asked whether he believed there was extraterrestrial intelligence:“Really, it’s okay to reserve judgment until evidence is in.”
Incidentally, we, humans, also think this way: We attribute our stomachaches to our last meal. Although this inference is normally correct in our daily life (as it would be for a rat falling sick in the wild), think of how our learning system can be “cheated” when the illness is artificially induced by anemetic unrelated to the food we ate.For example, consider how food aversions are established in cancer patients undergoing chemotherapy or radiotherapy treatments
This research was possible thanks to a one-time start-up research fund provided by Hofstra University to Oskar Pineño.Thanks are due to Jessica Zilski-Pinenofor her insightful comments on an earlier draft of this article.
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