NSM serotonergic state did not change wiring coupling of co-activity in 40 off-food C. elegans; an on-food decrease in 8 worms matched a drop in activity variance

Question: does the state of the serotonergic neuron NSM change how strongly the C. elegans connectome predicts co-activity? Approach: we used NeuroPAL-identified whole-brain GCaMP recordings of 40 off-food moving worms (Atanas 2023) and 8 on-food worms (Dag 2023). In each recording we divided frames into NSM-high and NSM-low halves. In each half we fitted pair correlations with neuron fixed effects plus gap-junction and chemical synapse counts (Cook 2019). We compared the change with splits by every other neuron class, circular NSM shifts, speed and time. Results: off food, NSM state did not change gap coupling (change -0.0004, 95% CI -0.0062 to +0.0054, level 0.127; the CI excludes changes above 5% of the level) or chemical coupling. On food, gap coupling was 21% lower in NSM-high halves (-0.022, CI -0.037 to -0.008, 7 of 8 worms; also with Witvliet adult-8 wiring). But NSM-high halves on food had a large drop in activity variance, and other neuron-class splits with a similar drop gave a similar decrease (-0.018). The NSM value minus this matched value was -0.004 (CI -0.015 to +0.008). After behaviour regression it was -0.001. Pairs with serotonin-receptor reporters showed no clear specific change. Conclusion: in these data the NSM state does not have a specific effect on the wiring rule of co-activity; the on-food decrease is a general property of low-variance epochs. Limitations: observational state, no serotonin mutants, only 8 on-food worms, food condition confounded with data set, connectomes from other animals, and uncorrected secondary tests.