Associative learning and memory inLymnaea stagnalis: how well do they remember? (original) (raw)

2003, The Journal of Experimental Biology

Molluscan model systems for the study of learning and memory This is not by any means an exhaustive review of invertebrate model systems that have been used to study the neuronal and molecular mechanisms of learning and memory; the interested reader is directed to two recent excellent reviews on this subject (Sahley and Crow, 1998; Chase, 2002). We have also restricted our discussion to gastropod molluscs, but this should in no way be taken to mean that the truly groundbreaking work on the mechanisms of learning and memory using 'worms' (e.g. Caenorhabditis elegans) or insects such as Drosophila is not worth mentioning or pursuing but rather that space limitations preclude their inclusion. For much the same reason, the fascinating studies using cephalopod molluscs (e.g. octopus), which exhibit very sophisticated learning and memory capabilities, will also not be reviewed here. Some of the first studies in the 'modern' search for the engram took the comparative physiological and psychological approach. For example, in the early 1900s, Piéron (1911), Dawson (1911) and Thompson (1917) used snails in attempts to discover how learning occurred. However, these studies were, by and large, forgotten, and it really was not until tests that were more natural and meaningful to the organisms were used that a full appreciation of the learning capabilities of gastropods became apparent. The 1960s saw a burst of activity that is still evident today to study how the nervous system is 'wired-up' to mediate specific behaviours and how changes in the behaviour brought about by training procedures are reflected or caused (the real goal) by changes in the activity of specific neurons. Thus, preparations such as Aplysia, Hermissenda, Pleurobranchaea and Tritonia gained popularity. Eric Kandel, with his share of the Nobel Prize for Medicine and Physiology in 2000, attained one of the pinnacles of science in part by using Aplysia. All the species mentioned above are marine creatures, and, with few exceptions (e.g. the land slug Limax and the land snail Helix), conventional wisdom from the 1970s through to the early 1990s was that the freshwater gastropods just did not have the 'right stuff' to be used in the quest for the Holy Grail. This review will focus on why that conventional wisdom was incorrect and why using Lymnaea might just be a very useful path to take to grasp the Grail in hand. Lymnaea as a model system for neurobiology Until the Dutch, under the inspired leadership of Professors Lever and Joose in The Department of Biology at Vrije Universeit in Amsterdam, adopted Lymnaea as their animal of choice for study in the early 1970s, Lymnaea was not often used in neurobiological research. The natural history of the 2097