How the nervous system encodes and stores memory remains an enigma in neuroscience. C. elegans has a simple nervous system consisting of as few as 302 neurons and its connectome is already revealed, thus making it an ideal system for analysis of the roles of each neuron or a certain neuronal circuit in the regulation of behaviors. Despite its simple nervous system, C. elegans has complex behaviors accompanied with associative learning, suggesting its simple nervous system is also plastic. For instance, C. elegans can memorize ambient temperature in association with the presence of food and migrate toward that temperature on a temperature gradient. This behavior, called thermotaxis, is achieved with a simple neuronal circuit consisting of a small number of neurons and has provided opportunities to dissect the molecular mechanisms of sensory perception, behavioral regulation, neural plasticity such as learning and memory. Interestingly, thermotaxis behavior itself is plastic; worms cultivated at 23°C and then transferred to 17°C merely for 3 hours already prefer 17°C. We have performed a forward genetic screen for genes responsible for this memory updating process. One of the mutant alleles identified from the screen, nj131, showed a slow-learning phenotype during temperature up-shift, but not during temperature down-shift. The slow-learning phenotype of this mutant was inherited in a semi-dominant manner. By combining the SNP mapping and the whole-genome sequencing, nj131 allele was then mapped to a gene locus encoding a potassium channel which belongs to a structural class with six transmembrane domains per subunit (6TM). We are now further characterizing the role of this gene in memory updating. Revealing genes and neuronal circuits important for thermal memory updating will pave the way for understanding the molecular identity of the memory and how the nervous system process the input and output the signals to regulate behaviors.