Both physics and neuroscience seek to understand how the edges and nodes of a network dictate its function. But until recently, it was not possible to quantitatively explore the relation between the structure and function of a biological neural network at brain scale and cellular resolution because no single brain had both a complete neuroanatomical map, called a connectome, and corresponding measurements of signal propagation with which to compare. To close this gap, we recently performed the first direct measurements of signal propagation at brain scale and cellular resolution in the nematode Caenorhabditis elegans by optically activating each neuron in the network, one at a time, and measuring the network’s response. These pump-probe style measurements reveal that neural signals often travel through the network in ways that are unexpected from wiring alone. For example, we measured a form of wireless signaling, extrasynaptic peptidergic signaling, that contributes to neural dynamics even though it is not visible from anatomy. These measurements, in combination with others from our group, are helping to reveal how neural network dynamics process sensory information and generate actions.