Thermotaxis in the nematode Caenorhabditis elegans is an ideal behavior to address decoding of decision-making, learning and navigation in the neural circuits. We are attempting to understand the roles of component neurons and neuronal connections of the thermotaxis circuit with optogenetics, calcium imaging and behavioral analysis. Thermosensory neuron AFD not only perceives temperature information, but also memorizes the temperature at which the animals were previously cultivated. This thermal memory is independent of synaptic transmission, since a cultured neuron AFD devoid of any synaptic connections enabled to form and maintain temperature memory. AFD neuron appears to send both excitatory and inhibitory signals to its postsynaptic interneuron AIY, thereby generating opposing thermotactic behaviors. We also found that the activity of RIA interneuron, which is postsynaptic to AIY, is highly stochastic and is inhibited by the temperature nearly corresponding to the thermal memory in AFD. Given that RIA interneuron sends signals to RMD/SMD moterneurons that regulates the head-bending movement, we suggest that the RIA is a decision-making neuron and that shutdown of the stochastic activity in RIA triggers switching of the behavioral modes from exploration to the memory dependent behavior.