A functional connectivity atlas of C. elegans measured by neural activation*

Neural processing and dynamics are governed by the details of how neural signals propagate from one neuron to the next through the brain. We systematically measured functional properties of neural connections in the head of the nematode Caenorhabditis elegans by direct optogenetic activation and simultaneous calcium imaging of 10,438 neuron pairs. By measuring responses to neural activation, we extracted the strength, sign, temporal properties, and causal direction of the connections and created an atlas of causal functional connectivity. We find that functional connectivity differs from predictions based on anatomy, in part, because of extrasynaptic signaling. The measured properties of the connections are encoded in kernels which describe signal propagation in the network and which we fit from the data. Using such kernels, we can run numerical simulations of neural activity in the worm's brain using exclusively information that comes from the data, as opposed to simulations based on the anatomical connectome which require assumptions on many parameters. We show that functional connectivity better predicts spontaneous activity than anatomy, suggesting that functional connectivity captures properties of the network that are critical for interpreting neural function.