Fig. 2: Modularity and functional specialization of interneurons.

a, Top, matrix of connections in the ‘center’ of the wiring diagram, with neurons clustered into two modules (modA and modO). Bottom, matrix of connections from center to large RS and ABD neurons in the periphery. b, Top, example connected pairs of modA neurons. Bottom, example connected pair of modO neurons (light and dark blue) and the overlap of their axons with the dendrite of an ABD internuclear cell (magenta). The grid in the background is the same in both images to facilitate comparison. c, Locations of reconstructed neuron somas (modA, orange; modO, blue) projected onto the horizontal plane and one-dimensional (1D) densities along the mediolateral (bottom) and rostrocaudal (left) axes. Closed circles are neurons with complete somas inside the reconstructed EM volume. Open circles are locations of the primary neurites exiting the top of the EM volume for cells with somas above the volume. The inset cartoon shows the region of the hindbrain in the figure. d, Postsynapses of neurons in modA and modO along with 1D densities. Every fifth postsynaptic density is plotted for clarity. e, Presynapses of neurons in modA and modO along with 1D densities. Every tenth presynaptic terminal is plotted for clarity. f, Schematic illustrating the definition of a potential (that is, false) synaptic connection identified when a presynaptic terminal (for example, axon 2) is proximal (red) to a postsynaptic density (for example, dendrite 1) but not actually in contact with it. g, Ratio of the number of within-module to the number of between-module synapses versus threshold distance for true and potential synapses. The table lists the actual true synapse densities for the data point with an asterisk (*). h, Ratio of numbers of synapses from neurons in modA and modO to peripheral neurons (ABD and RS).