Turning-associated neurons gates a sensorimotor response in C. elegans upstream of neuron AVA

A fundamental task of the brain is to integrate sensory cues with an animal’s current behavior to respond appropriately. But precisely how neural circuits integrate sensory and behavior signals remains unknown. To address this, we investigated C. elegans response to touch. C. elegans often respond to a mechanosensory stimulus by moving backward, called a reversal. Previously we found that C. elegans are less likely to reverse in response to mechanosensory stimuli delivered when it is in the midst of turn compared to stimuli delivered during forward locomotion. To explore the underlying circuit mechanisms, we optogenetically activated downstream interneurons in the mechanosensory pathway, either while the worm was moving forward or while it was turning. Activation of interneurons AIZ, RIM, AIB, or AVE, during forward locomotion was more likely to evoke reversals than during turning. Activation of neuron AVA, however, evoked reversals with similar likelihood regardless of whether the animal was moving forward or turning. Further, inhibiting turning-related neurons RIV, SMB, and SAAD, restored the animal’s response to mechanosensory stimuli, even during turns. Taken together, our measurements suggest a circuit mechanism in which signals from turning associated neurons act as a gate to disrupt or inhibit mechanosensory-related signals, and that these turning related signals act upstream of neuron AVA.