One-trial conditioned taste aversion in Lymnaea: good and poor performers in long-term memory acquisition (original) (raw)
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Critical period of memory enhancement during taste avoidance conditioning in Lymnaea stagnalis
PloS one, 2013
The present study investigated the optimal training procedure leading to long-lasting taste avoidance behavior in Lymnaea. A training procedure comprising 5 repeated pairings of a conditional stimulus (CS, sucrose), with an unconditional stimulus (US, a tactile stimulation to the animal's head), over a 4-day period resulted in an enhanced memory formation than 10 CS-US repeated pairings over a 2-day period or 20 CS-US repeated pairings on a single day. Backward conditioning (US-CS) pairings did not result in conditioning. Thus, this taste avoidance conditioning was CS-US pairing specific. Food avoidance behavior was not observed following training, however, if snails were immediately subjected to a cold-block (4°C for 10 min). It was critical that the cold-block be applied within 10 min to block long-term memory (LTM) formation. Further, exposure to the cold-block 180 min after training also blocked both STM and LTM formation. The effects of the cold-block on subsequent learning...
The Journal of Experimental Biology, 2007
In the majority of studies designed to elucidate the causal mechanisms of memory formation, certain members of the experimental cohort, even though subjected to exactly the same conditioning procedures, remember significantly better than others, whereas others show little or no long-term memory (LTM) formation. To begin to address the question of why this phenomenon occurs and thereby help clarify the causal mechanism of LTM formation, we used a conditioned taste aversion (CTA) procedure on individuals of the pond snail Lymnaea stagnalis and analyzed their subsequent behavior. Using sucrose as an appetitive stimulus and KCl as an aversive stimulus, we obtained a constant ratio of 'poor' to 'good' performers for CTA-LTM. We found that approximately 40% of trained snails possessed LTM following a one-trial conditioning procedure. When we examined the timewindow necessary for the memory consolidation, we found that if we cooled snails to 4°C for 30•min within 10•min after the one-trial conditioning, LTM was blocked. However, with delayed cooling (i.e. longer than 10•min), LTM was present. We could further interfere with LTM formation by inducing inhibitory learning (i.e. backward conditioning) after the one-trial conditioning. Finally, we examined whether we could motivate snails to acquire LTM by depriving them of food for 5•days before the onetrial conditioning. Food-deprived snails, however, failed to exhibit LTM following the one-trial conditioning. These results will help us begin to clarify why some individuals are better at learning and forming memory for specific tasks at the neuronal level.
Taste discrimination in conditioned taste aversion of the pond snail Lymnaea stagnalis
Journal of Experimental Biology, 2006
Lymnaea stagnalis has been widely used as a model for gaining an understanding of the molecular and behavioral mechanisms underlying learning and memory. At the behavioral level, however, it is still unclear how taste discrimination and CTA interact. We thus examined how CTA to one taste affected the feeding response induced by another appetitive food stimulus. We first demonstrated that snails have the capacity to recognize sucrose and carrot juice as distinct appetitive stimuli. We then found that snails can become conditioned (i.e. CTA) to avoid one of the stimuli and not the other. These results show that snails can distinguish between appetitive stimuli during CTA, suggesting that taste discrimination is processed upstream of the site where memory consolidation in the snail brain occurs. Moreover, we examined second-order conditioning with two appetitive stimuli and one aversive stimulus. Snails acquired second-order conditioning and were still able to distinguish between the different stimuli. Finally, we repeatedly presented the conditional stimulus alone to the conditioned snails, but this procedure did not extinguish the long-term memory of CTA in the snails. Taken together, our data suggest that CTA causes specific, irreversible and rigid changes from appetitive stimuli to aversive ones in the conditioning procedure.
Conditioned taste aversion with sucrose and tactile stimuli in the pond snail Lymnaea stagnalis
Neurobiology of Learning and Memory, 2004
A new form of taste aversion conditioning was established in the pond snail Lymnaea stagnalis. An associative memory, lasting 24 h, was produced in the pond snail with 20 pairings of 100 mM sucrose as the conditioned stimulus (CS) and mechanical stimulation to the head as the unconditioned stimulus (UCS). Animals exposed to reverse pairings of the CS and UCS failed to learn the association. The learning was characterized by a shift in the response to the UCS from a whole-body withdrawal response to the cessation of feeding behavior.
Developmental Changes in Conditioned Taste Aversion in Lymnaea stagnalis
Zoological Science, 1999
As the first step to study relationships between development and learning in the molluscan central nervous system, we examined developmental changes in acquisition and retention of a conditioned taste aversion (CTA) in the pond snail, Lymnaea stagnalis. We found that snails developed ability of a CTA as a long-term memory through three critical stages. Embryos in veliconcha started to respond to appetitive sucrose at the first critical stage. This response was in good agreement with morphological observations that embryos at this developmental stage seemed to be physically ready to eat. However, they could not associate this appetitive stimulus (conditioned stimulus: CS) with an aversive stimulus of KCl (unconditioned stimulus: UCS). At the second critical stage, embryos just before hatching acquired the CTA, but the conditioned response did not persist. Through this stage, they may acquire learning ability to safely seek out food in an external environment. At the third critical stage, immature snails with a 10 mm shell could use a long-term memory to maintain the conditioned response. This memory persisted for at least a month, showing that now they are able to maintain a long-term memory so that they can safely eat a variety of food when they cover wide territory to search for a mate. The present findings indicate that the development of learning ability in snails, which secures acquisition of better survival ability, is coincident with the major changes in their life cycle.
Another Example of Conditioned Taste Aversion: Case of Snails
Biology
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-tri...
The Yerkes-Dodson law and appropriate stimuli for conditioned taste aversion in Lymnaea
The Journal of experimental biology, 2015
The pond snail Lymnaea stagnalis can learn conditioned taste aversion and then consolidate it into long-term memory (LTM). A high-voltage electric shock was used as the unconditioned stimulus, where we have previously used KCl. We varied the strength of both the conditioned and unconditioned stimuli to determine whether the so-called Yerkes-Dodson law prevailed. This is an empirical relationship between the state of arousal and LTM formation, showing that there is an optimal level of arousal leading to memory formation. However, too little or too much arousal results in poorer LTM. We found here that the most appropriate stimuli to use in taste aversion training in Lymnaea were a 10 mmol l(-1) sucrose solution as the conditioned stimulus and a 3 s electric shock as the unconditioned stimulus.