Critical Period of Memory Enhancement during Taste Avoidance Conditioning in Lymnaea stagnalis

Abstract

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 and memory formation were also examined. We found no long lasting effects of the cold-block on subsequent memory formation. If protein kinase C was activated before the conditioning paradigm, snails could still acquire STM despite exposure to the cold-block.

Electrophysiological characteristics of feeding-related neurons after taste avoidance Pavlovian conditioning in Lymnaea stagnalis

“…Snails easily learn and form LTM following the TAC training. This has been demonstrated in many previous studies using slightly different USs and numbers of paired presentations 11 – 14 , 17 , 34 . As well, APC of the feeding response has also been frequently demonstrated 35 , 36 .…”

“…This topic of why some snails do not form LTM is not dwelt on but we might possibly learn more about the causal neuronal mechanisms underlying LTM by studying those that do not form LTM. Regarding the mechanisms of LTM formation, our recent studies indicated that a space training procedure where there is an interposition of a couple of hours between CS-US paired presentations effectively enhances the formation of LTM 11 , 13 . Depending on the criteria used the percentages of good vs. poor performers can vary greatly.…”

Memory block: A consequence of conflict resolution

“…Snails are able to consolidate the associative learning into long-term memory (LTM) (Benjamin et al, 2000;Otsuka et al, 2013;Takahashi et al, 2013;Lukowiak et al, 2014;Sunada et al, 2014). Here, we look at the ability of Lymnaea to learn and remember for many days not to respond to a food substance that normally elicits a feeding response.…”

The Yerkes-Dodson law and appropriate stimuli for conditioned taste aversion in Lymnaea

“…The pond snail Lymnaea stagnalis is an excellent model system to elucidate the causal neuronal mechanisms underlying learning and the formation of memory Otsuka et al, 2013;Takahashi et al, 2013;Lukowiak et al, 2014;Takigami et al, 2014). Here, we focus our attention on aversive conditioning of feeding behavior known as conditioned taste aversion.…”