Scientists create first detailed map of insect brain with 3,016 neurons

Researchers from Johns Hopkins and Cambridge universities have created the first-ever map of the wiring patterns of every neuron in the fruit fly larval brain.

The meticulously created connectome, which took 12 years to complete, depicts the locations of all 3,016 neurons in the fruit fly larval brain (Drosophila melanogaster). The 548,000 synapses that connect those brain cells allow the cells to communicate chemically with one another, which in turn causes electrical signals to be sent through the wiring of the cells.

Neurons in an organism's nervous system, including the brain, are linked to one another by synapses. By these contact locations, chemicals carrying information are transferred from one neuron to another, says the University of Cambridge.

Connectome: The map of 3016 neurons

The brain structures of the fruit fly larva are similar to those of the adult fruit fly and other larger insects. It possesses various behavioral capabilities, including learning and action selection.

A "connectome" is a map of the 3016 neurons that make up the brain of the larva of the fruit fly and the intricate network of neural pathways within it.

This is the most comprehensively mapped connectome of the human brain to date. Mapping fundamental brain regions, such as those of the roundworm C. elegans, which only has a few hundred neurons, represents a significant advancement over earlier efforts.

“The way the brain circuit is structured influences the computations the brain can do. But, up until this point, we haven’t seen the structure of any brain except in very simple organisms,” said Professor Marta Zlatic at the University of Cambridge’s Department of Zoology and the Medical Research Council Laboratory of Molecular Biology (MRC LMB).

“Until now, the actual circuit patterns involved in most brain computations have been unknown. Now we can start gaining a mechanistic understanding of how the brain works," she added.

Current technology is inadequate

The current state of technology does not allow for mapping the connectomes of more complex species, such as large mammals. Yet, because all brains are made up of networks of interconnected neurons, the researchers believe their new map will serve as a permanent reference for future studies of brain function in other animals.

The researchers created computer tools to recognize various circuit topologies and potential information flow channels in the insect's brain. They discovered that several of the structural characteristics resemble modern deep-learning architecture.

The next step is to explore further to learn more about, for instance, the brain circuitry necessary for particular behavioral processes, such as learning and decision-making, and to examine activity in the entire connectome when the insect is acting.

The study was published in Science Advance on March 10.

Study abstract:

A brainwide, synaptic-resolution connectivity map—a connectome—is essential for understanding how the brain generates behavior. However because of technological constraints imaging entire brains with electron microscopy (EM) and reconstructing circuits from such datasets has been challenging. To date, complete connectomes have been mapped for only three organisms, each with several hundred brain neurons: the nematode C. elegans, the larva of the sea squirt Ciona intestinalis, and of the marine annelid Platynereis dumerilii. Synapse-resolution circuit diagrams of larger brains, such as insects, fish, and mammals, have been approached by considering select subregions in isolation. However, neural computations span spatially dispersed but interconnected brain regions, and understanding any one computation requires the complete brain connectome with all its inputs and outputs.