How variety of time scales in memory could caenorhabditis elegans, a simple and compact neural circuit organism, form?

Caenorhabditis elegans is one of the novel model organisms, which has been studied on over 50 years. C. elegans has just 302 neurons and simple neural circuits, of which connectivity has already been revealed. In addition, tractable gene manipulation thanks to its genome source has made C. elegans the more ideal model organism. Since early times, many kinds of assay have elucidated that C. elegans forms short-term and long-term memory of various sensory modal stimuli such as mechanostimulus, temperature, odorants and gustatory cues. In addition, recent studies showed memory of worms transmitted through multiple generations existed. Like this, although this model animal is very simple, it exhibits various types of time scales in learning and memory with compact neural circuits. In this chapter, first we introduce learning and memory of C. elegans in each sensory modality and then discuss time scales of obtaining and retaining memory. Finally, we show perspective of learning and memory researches in C. elegans, indicating powerful tools recently developed.