Regulation of experience-dependent bidirectional chemotaxis by a neural circuit switch in Caenorhabditis elegans.

The nematode Caenorhabditis elegans changes its chemotaxis to NaCl depending on previous experience. At the behavioral level, this chemotactic plasticity is generated by reversing the elementary behaviors for chemotaxis, klinotaxis, and klinokinesis. Here, we report that bidirectional klinotaxis is achieved by the proper use of at least two different neural subcircuits. We simulated an NaCl concentration change by activating an NaCl-sensitive chemosensory neuron in phase with head swing and successfully induced klinotaxis-like curving. The curving direction reversed depending on preconditioning, which was consistent with klinotaxis plasticity under a real concentration gradient. Cell-specific ablation and activation of downstream interneurons revealed that ASER-evoked curving toward lower concentration was mediated by AIY interneurons, whereas curving to the opposite direction was not. These results suggest that the experience-dependent bidirectionality of klinotaxis is generated by a switch between different neural subcircuits downstream of the chemosensory neuron.