A big advance in mapping the structure of the brain

The cognitive abilities of a fruit-fly larva may not seem particularly noteworthy. This creature—the fly’s early, wormlike phase—is just about capable of sensing its environment, searching for food and avoiding predators. Its brain does not yet know how to walk, fly, or even properly see. And yet its limited capacity is still, in miniature, a useful model for what larger and more complex brains can do.

Researchers have now published the first complete map of the brain of such a larva. This “connectome”—the equivalent of a three-dimensional circuit diagram—charts the locations of a brain’s neurons as well as the synapses, the junctions where the brain cells pass information between each other. The structures of these circuits influence the kinds of computations a brain can do. Knowing how neurons are interconnected can give scientists a more mechanistic understanding of how the brain functions.