Insect brain mapping completed, a breakthrough for neuroscience
Brains are networks of interconnected neurons, and all brains of all species have to perform complex behaviors, such as navigating their environment, choosing food, or escaping predators. Now, a scientific team has succeeded in complete the first insect brain map.
This representation of the neural wiring of the brain of a fruit fly larva is, according to those responsible for it, a “landmark achievement” for neuroscience, which brings scientists closer to “true understanding” of the mechanism of thought.It opens the door to future brain research and will inspire new machine learning architectures. It is the largest complete brain connectome – diagram of neural connections – described to date. Details are published in the journal Science.
Behind this laborious research that lasted 12 years is a team from Johns Hopkins University (USA) and Cambridge (UK). “If we want to understand who we are and how we think, part of it is to understand the mechanism of thought,” says Joshua T. Vogelstein of Johns Hopkins, for whom the key lies in knowing how neurons are connected to each other.
The first attempt to map a brain-a 14-year study of the roundworm begun in the 1970s-resulted in a partial map and a Nobel Prize. Since then, partial connectomes have been mapped in many systems.including flies, mice, and even humans, but these reconstructions often represent only a small fraction of the total brain, explains Johns Hopkins. Only complete connectomes have been generated for several small species with a few hundred to a few thousand neurons: roundworm, ascidian larvae, and marine annelid larvae.
“This means that neuroscience has for the most part worked without circuit maps,” summarizes Marta Zlatic of the British university. “Without knowing the structure of a brain, we are guessing how computations are implemented, but now we can begin to understand mechanistically how the brain works,” she explains. Today’s technology, she adds, is not yet advanced enough to map the connectome of higher animals such as large mammals.
However, “all brains are similar -they are networks of interconnected neurons- and all brains of all species have to perform many complex behaviors: processing sensory information, learning, selecting actions, navigating their environment, choosing food, recognizing conspecifics, or escaping from predators.”
More than 3,000 neurons
The connectome of the fruit fly brood, Drosophila melanogasteris the most complete and extensive map of the insect brain. It includes 3,016 neurons and all the connections between them: 548,000.. Imaging alone took approximately one day per neuron.
To obtain a complete cellular-level image of a brain requires dividing it into hundreds or thousands of individual tissue samples, all of which have to be analyzed with electron microscopes before the laborious process of reconstructing the pieces, neuron by neuron, into a complete and accurate portrait of a brain. The team purposely chose the fruit fly (or vinegar fly) larva because, for an insect, the species shares much of its fundamental biology with humans.including a comparable genetic basis.
What we have learned about the code of the vinegar fly will have implications for the human code
Researchers scanned thousands of slices of the larval brain using a high-resolution electron microscope and reconstructed the resulting images into a map, meticulously noting the connections between neurons. They classified each neuron by the function it performs and discovered, for example, that the most active circuits in the brain were those to and from neurons in the learning center. They also developed computational tools to identify possible information flow pathways and different types of circuits.
The work showed circuit features that were “surprisingly” reminiscent of machine learning architectures, so the team hopes that continued study can Inspire new artificial intelligence systems..
“What we’ve learned about the vinegar fly code will have implications for human code,” Vogelstein says. “That’s what we want to understand: how to write a program that leads to a human brain network.” The methods and codes developed here are available to anyone who attempts to to map an even larger animal brain.
It is estimated that the brain of a mouse is one million times bigger than that of a baby fruit fly, which means that the possibility of mapping it is unlikely in the near future. Still, scientists hope to tackle it, they say, possibly within the next decade.
