The Male Fly Brain Is Now Fully Mapped

A collaboration between Janelia Research Campus and Google has completed the fruit fly connectome—both sexes, every synapse.

By The space-quantum Desk

Together, the two maps give neuroscience its first cross-sex wiring diagram for a complex animal brain.

The brain was sliced into thin sections, imaged by electron microscopy, then reassembled computationally—a pipeline that discovered over 300 million synaptic connections inside a nervous system of only roughly 150,000 neurons [1].

Generative AI stitched the slices back together, erasing gaps introduced at each cut. A separate model then traced individual cells through three-dimensional space, while additional models spotted and classified synapses [1]. Human proofreaders tuned the algorithms in an iterative loop, adjusting model "greediness" until results were reliable [1]. The whole process took roughly four years.

Comparing the two connectomes revealed 289 male-specific neurons, 71 female-specific ones, and 138 that were present in both sexes but formed a different shape and connections in males and females [1]. As the paper puts it, the location and connections of the sex-specific neurons "suggests a hierarchy in which sex differences primarily modify integrative and decision-making areas while sensory detection and the highly tuned motor interface remain more constant" [1].

What makes a mind different from another is less about total neuron count than about the architecture of connection—and now, for the first time, that architecture can be read like a schematic.