Fig. 4: Neuropil projections and analysis of crossing neurons.

a, Whole-brain neuropil–neuropil connectivity matrix. The main matrix was generated from intrinsic neurons, and afferent and efferent neuron classes are shown on the side. Incoming synapses onto afferent neurons and outgoing synapses from efferent neurons were not considered for this matrix. See Extended Data Fig. 5 for neurotransmitter-specific matrices. Neuropils are defined in Extended Data Fig. 1. C, centre neuropils; L, left neuropils; R, right neuropils. b, Cartoon describing the generation of the matrix in a. The connectivity of each neuron is mapped onto synaptic projections between different neuropils. \({{\bf{n}}}_{i}^{{\rm{out}}}\) and \({{\bf{n}}}_{i}^{{\rm{in}}}\) are vectors of numbers of synapses for each neuropil and neuron. c,d, Examples from the matrix in a with each render corresponding to one row or column in the matrix (c) and examples from the matrix with each render corresponding to one square in the matrix (d). e, Most neurons have pre- and postsynaptic locations in fewer than four neuropils. Insets show a closer view of the long tail of the distribution. NPs, neuropils. f, Renderings (subset of 3,000 each) and input and output fractions of neurons projecting to and from the SEZ. The SEZ is composed roughly of five neuropils (the AMMC has left and right homologues). Average input and output fractions were computed by summing the row and column values of the SEZ neuropils in the superclass-specific projection matrices. g, Fraction of contralateral synapses for each central brain neuron. h, Fraction of ipsilateral, bilateral and contralateral neurons projecting to and from the centre neuropils per superclass. Scale bars, 100 µm.