Olfactory learning and navigation behavior of C. elegans in a controlled odor environment*

Animals flexibly adjust behavior in response to sensory environments after learning experiences. In the nematode worm C. elegans, associative learning with an olfactory cue modulates chemotactic behavior towards the cue if it was paired with food or starvation. However, it is unknown how olfactory learning alters sensory-motor processing for any specific navigation strategy. For example, whether it adjusts the bias in a biased random walk, or alternatively modulates other navigational strategies adaptively during the task. The biophysics with which worms sense airborne olfactory cues is also not well understood. Here we investigate butanone-odor associative learning by constructing a flow chamber to precisely measure the odor concentration experienced by worms during odor-guided navigation. We control airborne cues to form a stationary chemical landscape, monitor concentration with an array of digital odor sensors, and track the trajectories and posture of worms in the environment. We developed a statistical model with a mixture of navigation strategies to characterize chemotaxis behavior. This model captures different strategies previously reported in worms, including biased random walk (klinokinesis) and gradual change in the head angle towards high concentration (klinotaxis). With our apparatus and proposed model, we will discuss progress towards quantitatively characterizing the bi-directionally modulated navigation strategies in learned odor-guided navigation.