Researchers Map Neural Connections of Fruit Fly Brain

A neuronal wiring diagram of the adult fly brain, which comprises 139,000 neurons and more than 50 million synapses.

Photo:  TYLER SLOAN/PRINCETON UNIVERSITY

An NIH-supported scientific team revealed the first complete map of the neural connections of the common fruit fly brain. The map provides a wiring diagram, known as a connectome, and is the largest and most complete connectome of an adult animal ever created.

This work offers critical information about how brains are wired and the signals that underlie healthy brain functions. The study, which details over 50 million connections between more than 130,000 neurons, appears as part of a package of nine papers in Nature.  

The connectome map details the full set of cell classes in the fruit fly brain, identifying different types of neurons and chemical connections, or synapses, between neurons. It also provides insight into the type of neurotransmitter (chemicals such as dopamine or serotonin) secreted by each neuron.

The researchers also created a map of projections between brain regions, known as a projectome, that tracks the organization of the hemispheres and behavioral circuits within the fly brain. It allows for the detailed mapping of specific brain circuits that control behavior, such as the ocellar brain circuit, which takes in visual stimuli and outputs behavioral changes that orient the fly’s body during flight. 

In a companion paper, the researchers provided additional details critical for researchers who will use the connectome to advance our understanding of brain physiology and behavior.

The fruit fly is capable of surprisingly advanced cognition and behavior, making it an ideal candidate for this initial connectome project. For example, they can form long-term memories, engage in social interactions and navigate over large distances.

Now that the fruit fly connectome has been established, the same methodology could be used to rapidly create similar maps in larger-brained animals. The new map might serve as a reference to understand how a host of human mutations affect brain connections.