C. elegans Thermotaxis

In the thermotaxis assay, C. elegans is placed on an agar plate bearing a shallow linear or radial temperature gradient, and its movement relative to its prior cultivation temperature (T_c) is recorded. Hedgecock and Russell (1975) first showed that well-fed worms migrate toward, and then track along isotherms near, the temperature at which they were raised — a behavior they could disrupt with mutations, establishing thermotaxis as a genetically tractable sensory behavior.

The behavior is built on a small thermosensory circuit. Mori and Ohshima (1995) used laser ablation to identify the AFD sensory neuron as the principal thermosensor, with the AIY and AIZ interneurons biasing thermophilic versus cryophilic movement. Because the preferred temperature is set by recent experience and can be re-trained by re-cultivation, thermotaxis doubles as an assay of temperature memory and associative plasticity, making it a favorite system for dissecting how sensory experience is stored.

ConductVision reconstructs each animal’s trajectory from markerless video registered to the plate’s thermal geometry, then computes the thermotaxis index, isothermal-tracking length, migration bias and preferred-temperature zone automatically. Isotherm-tracking — historically scored by hand from track photographs — is detected directly from the path, and population heat maps reveal thermophilic, cryophilic or atactic phenotypes at a glance.

Thermotaxis is applied in thermosensation research, in studies of experience-dependent plasticity and aging, and in screens of sensory-transduction and synaptic mutants. Gradient linearity and stability, accurate registration of the temperature field to the video frame, and consistent cultivation history are the key variables to control; throughput is high because many animals can be scored per gradient plate.