Maps of all the connections in the nervous system of both sexes (male and hermaphrodite) of the adult nematode worm Caenorhabditis elegans are presented in this week’s Nature. The findings represent the most complete neural maps (or connectomes) of C. elegans published to date and allow comparisons between the nervous systems of the sexes to take place. The maps could help to decipher the neural circuits responsible for the worm’s behaviour.

C. elegans is an important model organism for neuroscience research. Previous studies have described the connectomes for sections of the male C. elegans and the nervous system of the hermaphrodite.

Scott Emmons and colleagues build on this work by mapping the circuitry of the male head of C. elegans using a series of electron micrographs. The authors then combined these with previously published micrographs to generate whole-animal connectomes, including a reconstruction of the connections in the hermaphrodite nervous system. Their method allowed them to identify more connections than reported in earlier research, and they were able to provide each connection with a location and an indirect measure of its strength, based on their physical size. The authors also found that up to 30% of the connections may differ substantially in strength between the sexes. They note that their connectomes should be considered conceptualizations as they were constructed from micrographs of multiple animals.

In an accompanying News & Views article, Douglas Portman writes that the findings mark “a major step forward in the attempt to understand how a brain’s function emerges from its form.”