For years, scientists from HHMI Janelia, Google Research, and other collaborators worked to reconstruct every neuronal connection in the brain and central nervous system of an adult male fruit fly. The result is a map with more than 166,000 neurons, a record figure for this species and a new resource for studying how the brain works.
Can a fly help us better understand human neuroscience? Although its brain is tiny, it shares basic principles of neuronal organization. Its nervous system is also simple enough to study in great detail, yet complex enough to reveal how stimuli are transformed into actions.
1. A map with more than 166,000 neurons
The first visualization shows selected neurons from the fly’s brain and ventral nerve cord, a structure that is comparable, to some extent, to the human spinal cord.
Most of its senses are concentrated in the head. That is where you find its large compound eyes and a retractable proboscis that it uses to detect odors and consume liquid food. Sensory neurons gather information from the environment and transmit it along different pathways to motor neurons that control movement.
The map makes it possible to observe these connections as a complete network instead of studying each neuron in isolation.
2. From the brain to movement through artificial intelligence
Viewed from above, the fly has two enormous eyes connected to the central brain. From there, a thick cord of nerves links the brain to the rest of the body, where motor neurons coordinate different behaviors.
To build this representation, the researchers sliced the fly’s brain and body into extremely thin sections. They then captured images of every slice and used computing and artificial intelligence to combine millions of two-dimensional images into three-dimensional neuronal shapes.
AI does not replace scientists in this process. It helps process an amount of imagery that would be impossible to analyze manually at the same speed.
Understanding the structure of these connections makes it possible to ask better questions about how the brain works. Which pathway activates a response? Which neurons filter the information? Where does a visual signal become an instruction to move?
3. Inside a network with nearly 11,700 types of neurons
The male fly’s central nervous system contains 11,691 types of neurons. These cells can be classified by their size, shape, function, gene expression, and other traits.
The visualization begins with neurons located at the center of the brain and body. It then moves toward the outer layers until it reaches the neurons in the limbs. The result is a kind of journey through the internal architecture of this nervous system.
Classifying more than 166,000 neurons required combining the expertise of specialists with computing and AI tools. This type of work belongs to connectomics, a field that seeks to accurately reconstruct how brain cells connect to one another.
4. What changes between male and female brains
Most neurons in male and female flies are similar. However, there is one group of neurons specific to each sex and another set known as dimorphic neurons, which are present in both sexes but connected differently.
One of the images compares the AOTU012 neuron in a male brain and a female brain. This neuron participates in processing sensory and taste signals. Although it appears in both brains, its connections with other neurons can vary.
Some connections are shared, while others are exclusive or different depending on sex. These variations could help explain how the same species develops different behaviors, especially in areas such as perception and courtship.
5. From visual stimulus to action
The new map also shows pathways that connect vision with movement. In one of them, visual neurons R1-R6, shown in purple, transmit information to the motor neuron DNg13, shown in green.
Several intermediate stages appear between these two ends. One of them is the LoVP92 neuron, found only in males and associated with the love spot, a region linked to courtship behavior.
This pathway helps illustrate how an animal can detect something in its environment and respond with a specific action. Seeing, interpreting, and moving are not separate processes: they are part of a chain of connections that can now be observed with unprecedented detail.
A resource for studying the brain
Alongside this map, three studies were published using its data to investigate visual systems, taste, and social behavior. The project also expands on an earlier complete map of the brain of a female fruit fly.
The importance of this advance is not limited to improving our understanding of flies. Connectomics needs methods capable of analyzing enormous volumes of information, and AI is helping scale that work. With increasingly complete maps, scientists can move from asking which neurons exist to investigating how their connections produce behavior.
A fly’s brain fits in a tiny space, but its connections raise enormous questions. And when those connections can be seen, classified, and compared, neuroscience moves beyond observing a black box and begins to study a system with greater precision.
Original source
https://blog.google/innovation-and-ai/technology/research/male-fruit-fly-brain-map