Understanding how neural perturbations propagate in the nervous system is important for understanding neural dynamics, to elucidate specific circuits, and to reveal how neuroanatomy relates to neural function. Here, we systematically perturb individual neurons in C. elegans while measuring the responses of all neurons in its brain in order to directly measure functional connectivity at brain scale and cellular resolution. Specifically, we measure the sign, strength, direction, and temporal properties of the connections between neurons. We present a preliminary functional connectome, currently with 68 neuron classes from 24 animals (including mutants), comprising more than half of all neuron classes. Our preliminary atlas comprises more than 900 stimulation-whole-brain-response events. We investigate the stereotypy and timescale of evoked responses in the network, and compare connections to the known connectome and gene expression data. We explore in detail the role of one specific well-characterized neuron, RID, which outputs neural signals almost exclusively via extrasynaptic communication. We use this neuron to both validate our system and compare against predictions from gene expression data. We identify 20 neurons that respond to RID activation at timescales consistent with extrasynaptic communication. 18 of them were predicted from recent gene expression data (CeNGEN) to express receptors for transmitters released by RID, and two more were predicted to receive indirect signals from RID. This demonstrates that our direct measures of functional connectivity resolve wireless signaling between neurons that would not otherwise be visible in the wired connectome.