Closed-loop targeted optogenetic stimulation of C. elegans populations*

We present a worm tracking setup for closed-loop tracking and optogenetic stimulation of multiple C. elegans worms. The system addresses three specific challenges: it delivers illumination targeted to specific portions of the worm's body, it increases throughput, and it delivers closed-loop stimuli triggered on the worm's behavior state. We demonstrate this new method by investigating how competing mechanosensory stimuli are processed. We use the instrument to optogenetically activate the anterior and posterior soft touch neurons. We find that the probability of reversal is primarily dependent on anterior stimulus intensity, while the probability of sprinting forward depends on both the anterior and posterior stimulus intensities. To understand how current behavior state affects sensory processing, we delivered almost 10,000 stimulus events to the worms during turn onset. With higher statistical power we confirmed our previous finding that the probability of reversal in response to soft touch stimulus is reduced during turns in comparison to forward locomotion. By providing orders of magnitude greater throughput, we expect this device to make accessible new types of investigations.