“The Structure of the Nervous System of the Nematode Caenorhabditis elegans” was published in 1986 in the Philosophical Transactions of the Royal Society B by John G. White, Eileen Southgate, J. Nichol Thomson, and Sydney Brenner of the MRC Laboratory of Molecular Biology in Cambridge. Often called “the mind of a worm,” it was the first complete wiring diagram - a connectome - of any animal’s nervous system.
The achievement took roughly a decade of painstaking work. The team cut the millimetre-long worm into thousands of ultra-thin slices, photographed each under an electron microscope, and traced by hand how every nerve cell connected to every other. The adult hermaphrodite C. elegans has precisely 302 neurons, and the paper reconstructed the morphology of each one and mapped roughly 5,000 chemical synapses, 2,000 neuromuscular junctions, and 600 electrical gap junctions joining them.
The work mattered far beyond a single worm. It established the term and the method of connectomics: the idea that you could understand a nervous system by reconstructing its complete physical wiring. Because C. elegans always has the same neurons in the same arrangement, the map became a permanent reference that researchers still use, and a benchmark for the much larger connectome efforts that followed in flies and mice.
The honest limit, debated ever since, is that a static wiring diagram is not the same as understanding behavior. Knowing every connection did not by itself explain how the worm moves, senses, or learns - which is part of why projects like OpenWorm later tried to turn the connectome into a working simulation.