C. elegans Chemotaxis

In the chemotaxis assay, Caenorhabditis elegans is released on an agar plate carrying a spatial gradient of a soluble or volatile chemical, and its movement toward (attractant) or away from (repellent) the source is scored. The behavior is driven by a compact set of amphid chemosensory neurons: Bargmann, Hartwieg and Horvitz (1993) mapped volatile attraction to the AWA and AWC neuron pairs (for example diacetyl and isoamyl alcohol), while water-soluble cues are sensed largely by the ASE gustatory neurons. Because the wiring is known to single-neuron resolution, chemotaxis is one of the most tractable sensory behaviors in any animal.

C. elegans navigates the gradient using two interleaved strategies — a biased random walk (klinokinesis), in which the rate of reorienting "pirouettes" rises when the animal moves down-gradient, and gradual weathervane steering (klinotaxis). Pierce-Shimomura, Morse and Lockery (1999) quantified the pirouette mechanism, and Gray, Hill and Bargmann (2005) described the underlying reversal-and-omega-turn navigation circuit. Conditioned variants of the assay, in which an odorant is paired with food or starvation, turn chemotaxis into an assay of associative learning and sensory adaptation.

ConductVision scores chemotaxis directly from markerless overhead video. It localizes every worm against the agar background, computes the chemotaxis index from end-point or time-resolved counts, and reconstructs individual trajectories to extract run length, bearing to source, pirouette frequency and approach speed — read-outs that previously required manual end-point counting. Trajectory overlays and population heat maps make gradient navigation visible at a glance.

The assay is widely used in sensory neuroscience, in screens of signal-transduction mutants, and in research models of neurodegeneration and chemical neurotoxicity, where blunted chemotaxis is a sensitive phenotype. Throughput is high — dozens to a few hundred young adults per plate — so chemotaxis scales well to genetic and compound-screening workflows. Gradient stability, plate humidity, and consistent worm staging are the main factors to control across replicates.