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Humans vs. flies -

Sebastian Seung, a professor of computer science and neuroscience at Princeton University and a co-leader of the research project team, posed a compelling question: "Why should we care about the brain of a fruit fly?" His answer is simple, yet profound: understanding how any brain functions can provide valuable insights into the workings of all brains.

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Demystifying flies -

Often dismissed as annoying pests, flies have played a significant role in human culture throughout history. From art and literature to folklore and superstition, these tiny insects have captured our imagination and held deep symbolic meaning.

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Bad rap -

In ancient Egyptian culture, flies were associated with warfare, death, and destruction. The "Order of the Golden Fly" was an award given to brave soldiers, reflecting the insect's persistence and resilience. Flies were also seen as messengers of the underworld, guiding the souls of the dead.

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They matter for the environment -

Flies serve as important bioindicators, offering valuable insights into environmental health. Certain species are highly sensitive to pollution, and their presence or absence can reveal the state of an ecosystem.

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Flying into scientific breakthrough -

Fruit flies have helped researchers study inheritance mechanisms, developmental biology, and signal transduction pathways for more than a century. They have also played a crucial role in understanding the genetic basis of diseases, including cancer and neurodegenerative disorders.

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Rebranding -

From being reviled as symbols of decay to being celebrated as crucial contributors to scientific progress, flies have played a vital role in advancing our understanding of biology, medicine, and environmental sustainability.

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They are more similar to us than we think -

Fruit flies share approximately 60% of human genes, making them valuable models for studying human biology and disease. Their similarities to humans, including aging patterns, responses to caffeine, and courtship behaviors highlight the potential insights that can be gained from studying their brains.

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Brainy buddies -

Even though they are smaller than a pinhead, fruit fly brains are incredibly complex structures capable of performing sophisticated tasks. By studying these neural circuits, scientists have gained valuable insights into why flies are so difficult to swat, for example.

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Why are they so difficult to swat? -

Flies’ vision circuits allow them to detect the direction of an approaching threat with incredible precision. When faced with our rolled-up newspaper, their vision circuits send a strong jumping signal to the legs facing away from the danger, enabling them to react instinctively–literally faster than the speed of thought.

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Pioneers -

Brain wiring diagrams, known scientifically as connectomes, provide an actual map that scientists can then use to compare and expand to other species. Up until recently, researchers only had connectomes of a simple worm, which has 300 wires, and a maggot, which has 3,000.

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Scientists are all in -

The development of the fly's brain diagram was a monumental undertaking that required the collaboration of an international team of scientists. The ambitious assembly sounds straight out of a Marvel movie, as researchers formed the FlyWire Consortium.

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How do you go into a fly’s brain? -

To create the wiring diagram, scientists meticulously sliced a fly brain into 7,000 sections using a microscopic technique akin to grating cheese. Each slice was then photographed and digitally reconstructed. An electron microscope was used to visualize structures as small as four-millionths of a millimeter.

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AI to the rescue -

The researchers then turned to artificial intelligence to analyze the millions of images and trace the intricate network of neurons and synaptic connections within the fly's brain.

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Manual work -

Despite its capabilities, artificial intelligence was unable to fully automate the process. Researchers had to manually correct over three million errors in the generated map. This Herculean task required the combined efforts of a global team of scientists and volunteers.

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Connecting the dots -

But there was still plenty of work to be done. Without a description of what each individual neural connection does, the map would be meaningless, this according to Philipp Schlegel of the Medical Research Council's Laboratory of Molecular Biology.

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Brain GPS -

In Schlegel’s compelling analogy, the brain map is the equivalent of Google Maps for the mind. The diagram lays out the pathways between neurons, like streets and buildings. “However, to truly understand the brain's function, we need to add the equivalent of street names, town names, business hours, phone numbers, and reviews. Only then can we navigate this complex landscape and extract meaningful information," Schlegel explains.

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Deep diving -

By analyzing the brain map, researchers have identified distinct neural circuits responsible for various functions. For example, the circuits involved in movement are located at the base of the brain, while those for visual processing are situated towards the side.

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Eureka moment -

Visual processing requires significantly more computational power than movement, resulting in a larger number of neurons involved in these circuits. While scientists knew that separate vision and movement circuits existed, the connections between them remained a mystery until now.

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Discoveries -

In total, the researchers have identified around 140,000 neurons—98% of which have been categorized—and over 50 million synapses.

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Discoveries -

Using the detailed brain map, researchers have identified specialized neurons with distinct functions. 'Interrogator' neurons integrate various types of information, while 'broadcaster' neurons may coordinate activity across different neural circuits. Additionally, a specific circuit responsible for halting a fruit fly's movement has been discovered.

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Why are our brains still a mystery? -

The human brain is significantly larger and more complex than a fly's, which presents an enormous challenge for complete mapping.

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Stepping stone -

Having a complete connectome of a fly and its 130,000 wires is an amazing technical feat that paves the way for finding the connectomes for larger brains such as the mouse and, maybe in a few decades, our own.

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Technical issues -

Current technology limitations prevent us from capturing the intricate details of our neural network. Brain scans can reveal some aspects of the brain's wiring, but even the most advanced technology provides only a partial glimpse of its intricate network.

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Decoding the human brain -

So if we have a million times as many brain cells, or neurons, than the fruit fly that was studied, how can the wiring diagram of an insect brain actually help scientists learn how we think?

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Future studies -

Schlegel predicts that this new brain map will usher in a wave of discoveries in neuroscience within the next few years. By studying the fruit fly brain map, researchers aim to gain a deeper understanding of how a healthy brain functions.

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The cure for psychiatric disorders? -

By mapping the neural connections in specific regions of the human brain, researchers hope to shed light on the underlying causes of neuropsychiatric and other brain disorders. As John Ngai, director of the National Institutes of Health's Brain Initiative, emphasizes, “We cannot fix what we do not understand. This is why understanding the brain's wiring is so crucial.”

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It will take time -

Mapping the entire human brain, with its 86 billion neurons and trillions of connections, is a daunting task. As our brains are roughly a million times more complex than the fruit fly brain, completing a wiring diagram would require a staggering amount of data—equivalent to all of the world's internet traffic for a year.

Sources: (FlyWire) (Nature) (BBC) (The Guardian) (Harvard Medical School) (Medium)

See also: Are male and female brains different?

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