All the neurons and connections in the fruit fly’s brain have been mapped for a second time. A joint effort by biologists at the Howard Hughes Medical Institute’s Janelia Research Campus and computer scientists at Google revealed more than 300 million synaptic connections in the brain. The fruit fly’s nervous system consists of approximately 150,000 neurons; only a portion of them are located in its brain.
The researchers divided the fly’s brain and part of its ventral nerve cord into numerous slices at regular intervals. These slices, imaged using electron microscopy, were reassembled with computer models. While generative AI corrected gaps and distortions caused by the slicing process, other models traced cell membranes to reconstruct the shapes of neurons in three-dimensional space. Additional models identified synapses and classified their types. Human supervisors fine-tuned the models’ accuracy in identifying synapses through feedback. It took approximately four years to progress from dissecting the brain to completing the connection map.
This map, known as the Connectome, shows the location of every neuron in the brain and the synaptic connections it forms with other neurons. These connections determine the processing of sensory inputs, the routing of information to relevant centers, and outputs such as memory formation or muscle movement. The researchers expect the map to provide neuroscientists with a detailed foundation for studying how the brain works.
Together with the previously completed female fly connectome, the new study made it possible to examine the differences between male and female brains. The researchers identified 289 male-specific and 71 female-specific neurons. They found that 138 neurons present in both sexes formed different structures and connections in males and females. These differences could not always be explained directly by the doublesex (dsx) and fruitless (fru) genes, which play a role in sex determination. Sex-specific neurons were concentrated mostly in higher-level processing and decision-making pathways, away from basic sensory processing or motor control.
The researchers state that the methods developed for mapping the fly brain could be applied to more complex organisms. However, it is said that dozens of connectomes would be needed to reliably assess individual differences and that the process would need to be carried out in less than four years.
Why it matters
This study provides a usable reference infrastructure for neuroscientists seeking to examine how the brain functions through the organization of connections between individual cells rather than through the cells themselves. The map could make it easier to test which clusters of connections play a role in processes ranging from sensory information to decision-making and motor outputs; in particular, the fact that the differences between male and female flies cannot be explained solely by sex-determining genes shifts the research question toward connection architecture. The concentration of sex-specific neurons in higher-level processing pathways enables a detailed examination of the relationship between basic senses and behavioral decisions. However, many maps and faster production are needed to distinguish individual differences. The extent to which the methods can be applied to more complex organisms remains an open question.
Background
Second, FikirPilot is not a new name in the archive: we published a news article mentioning this name in the last 90 days; that article is dated 24 August 2026.