Abstract
Simple SummaryIt is important to decide what to eat and what not to eat in the life. Children are likely to reject new foods. When eating a new food results in a negative experience, the child will avoid that specific food in the future. This phenomenon is called ‘conditioned taste aversion’ in mammals, and it is considered necessary for survival by preventing subsequent ingestion of sickening foods. Many researchers study the same kind of phenomenon in invertebrates, too. For example, the formation of conditioned taste aversion was found in the pond snail, Lymnaea stagnalis, with the selective associability between a sweet sucrose solution and a bitter KCl solution. A sweet food attracts many kinds of animals, resulting in the feeding response, whereas a KCl solution is an aversive stimulus, inducing a withdrawal response in snails. After repeated temporally-contingent presentations of these two stimuli, the sucrose solution no longer elicits a feeding response, and this phenomenon persists for a long term. In the present review, we first outline the mechanisms of conditioned taste aversion in mammals, then introduce the conditioned taste aversion in snails, and compare them. Furthermore, the molecular events in snails are discussed, suggesting the general mechanism in conditioned taste aversion.Conditioned taste aversion (CTA) in mammals has several specific characteristics: (1) emergence of a negative symptom in subjects due to selective association with a taste-related stimulus, (2) robust long-term memory that is resistant to extinction induced by repeated presentation of the conditioned stimulus (CS), (3) a very-long-delay presentation of the unconditioned stimulus (US), and (4) single-trial learning. The pond snail, Lymnaea stagnalis, can also form a CTA. Although the negative symptoms, like nausea, in humans cannot be easily observed in invertebrate animal models of CTA, all the other characteristics of CTA seem to be present in snails. Selective associability was confirmed using a sweet sucrose solution and a bitter KCl solution. Once snails form a CTA, repeated presentation of the CS does not extinguish the CTA. A long interstimulus interval between the CS and US, like in trace conditioning, still results in the formation of a CTA in snails. Lastly, even single-trial learning has been demonstrated with a certain probability. In the present review, we compare, in detail, CTA in mammals and snails, and discuss the possible molecular events in CTA.
Highlights
Humans tend to reject new and unfamiliar food items
Findings regarding various types of conditioned taste aversion (CTA) have revealed the following common characteristics: (1) CTA is considered necessary for survival by preventing subsequent ingestion of sickening foods
unconditioned stimulus (US) alters the response to the conditioned stimulus (CS), resulting in a conditioned response (CR), which is similar to the unconditioned response (UR)
Summary
Humans tend to reject new and unfamiliar food items. For example, before eating the local cuisine when visiting a foreign country, we may first confirm whether the food item is hot, bitter, or sweet by querying the local residents. Findings regarding various types of CTA have revealed the following common characteristics: (1) CTA is considered necessary for survival by preventing subsequent ingestion of sickening foods This ability is considered an adaptive trait or survival mechanism by which the body avoids ingesting sickening substances before they can cause harm, resulting in robust maintenance of long-term memory for the CTA. The association between the CS and US alters the response to the CS, resulting in a conditioned response (CR), which is similar to the UR According to this definition, the use of CS and US seems odd in CTA, because the food CS is not neutral for the UR or CR that demonstrates that subjects do not eat the food. Our aim with this review is to convince the reader that invertebrate studies are very useful for studying the mechanisms underlying mammalian learning and memory
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