Analyses of Neural Circuits Governing Behavioral Plasticity in the Nematode Caenorhabditis elegans

Behavioral plasticity is subjected to various sensory stimuli, experiences, and physiological states, representing the temporal and spatial patterns of neural circuit dynamics. Elucidation of how genes and neural circuits in our brain actuate behavioral plasticity requires functional imaging during behavioral assays to manifest temporal and spatial neural regulation in behaviors. The exploration of the nervous systems of Caenorhabditis elegans has catalyzed substantial scientific advancements in elucidating the mechanistic link between circuit dynamics and behavioral plasticity. The analyses of the nervous system of C. elegans have technologically flourished owing to the development of optogenetic instruments and fluorescent protein-based imaging compatible with its optically transparent body and the understanding of its completely revealed neural connectome and gene expression profiles at single-neuron resolution (The C. elegans Neuronal Gene Expression Map & Network, CeNGEN project). Using examples of the two temperature learning behaviors in C. elegans, this chapter delves into a selection of pivotal imaging tools, including genetically encoded calcium indicators, biosensors for second messenger imaging, and their usage in freely moving worms that have propelled our grasp of sensory representation in C. elegans neural circuits. To further connect the circuit dynamics to behavioral plasticity, this chapter will focus on technological advancements enabling simultaneous imaging and tracking system together with methodologies to quantify multiple behavioral elements of freely behaving C. elegans in a dynamic environment.