Scientists have produced the most comprehensive map of a brain to date, which traces every neural connection of a larval fruit fly, making it a groundbreaking achievement in neuroscience.
The map of the larval fruit fly brain is a significant step towards understanding the mechanism of thought, an essential part of understanding who we are and how we think, said Joshua T. Vogelstein, the senior author and a biomedical engineer specializing in data-driven projects, including connectomics, the study of nervous system connections.
The larval fruit fly is an archetypal scientific model with brains comparable to humans.
Years in the Making
Scientists have been trying to map a brain since the 1970s when the first attempt to map the brain of a roundworm started. Since then, partial connectomes have been mapped in various systems, including flies, mice, and humans, but they only represent a small fraction of the total brain.
The team's connectome of a baby fruit fly, Drosophila melanogaster larva, is the most comprehensive map of an entire insect brain ever created, with 3,016 neurons and 548,000 connections.
Mapping the brain is an intricate and time-consuming process, and generating a full cellular-level picture of the brain requires slicing it into hundreds or thousands of individual tissue samples, which have to be imaged with electron microscopes before the lengthy task of reconstructing all those pieces of neuron by neuron into a complete and accurate portrait of the brain can commence.
The team chose the fruit fly larva specifically because it shares a significant part of its fundamental biology with humans, including a similar genetic foundation, and possesses complex learning and decision-making behaviors, making it a valuable model organism in neuroscience.
Furthermore, its relatively compact brain can be imaged, and its circuits reconstructed within a reasonable timeframe. It took a day to image each neuron, and Cambridge researchers manually studied high-resolution images of the brain, tracing individual neurons and linking their synaptic connections.
Johns Hopkins then used original code to analyze the brain's connectivity for more than three years, developing techniques to find groups of neurons based on shared connectivity patterns and analyzing how information could propagate through the brain.
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Brain's Busiest Circuits
The team managed to map every neuron and connection in the fruit fly larva brain, categorizing each neuron based on its function. They discovered that the brain's busiest circuits were those connected to and from neurons of the learning center.
According to Vogelstein, the methods developed by Johns Hopkins are useful for any brain connection project, and their code is available to anyone attempting to map larger animal brains.
He also mentioned that scientists are expected to take on the mouse brain, which is larger than the fruit fly's, possibly within the next decade. Other teams are already working on a map of the adult fruit fly brain.
The circuit features discovered in the fruit fly larva brain are similar to those found in powerful machine learning architectures, as per the team. They believe that further studies will reveal more computational principles and possibly inspire new artificial intelligence systems.
Vogelstein stated that the team's discoveries about the fruit fly's code would have implications for understanding the human brain network. He noted that their goal is to comprehend how to write a program that leads to a human brain network.
The findings of the team was published in the journal Science.
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