On March 10th, the "brain map", the most complete atlas of the whole brain neurons of Drosophila larvae so far, was published online in the international academic journal Science. This research result will support future brain science research and inspire people to design a new generation of artificial intelligence system.
On March 7, Albert Cardona, one of the authors of the paper and a professor at Cambridge University in the UK, told 澎湃 Technology, "This laid the foundation for future research on how the brain changes in disease and evolution."
Albert cardona said that an exciting discovery is that the powerful computing power of his brain comes not only from the connection between one neuron layer and the next, but also from the cross-layer connection. This type of neural structure can minimize the number of neurons needed and reduce the metabolic cost without affecting the computing power.
Albert cardona said, "Among these key findings, what I want to say is that we found how strongly the brain is recursive. This is another feature of the powerful artificial neural network architecture. " The most recursive neural structure is related to the input and output neurons of the brain learning center.
The researchers said that as more "brain maps" of larvae and other related species are drawn, people will be able to better understand the way and changes of brain "wiring" and reveal more calculation principles.
Joshua T. vogel, another correspondent of the paper and an assistant professor at Johns Hopkins University in the United States, told the media how to write a program or code for a human brain network. "This is what we want to know." "Our knowledge of the code of fruit flies will have an impact on the code of human beings. "
After 12 years’ efforts, the researchers finally mapped the neuronal connectome in the brain of Drosophila larvae, which contained 3016 neurons and 548,000 synapses.
What is a "brain map"?
The human brain is composed of various types of neuron cells, and the axons of these neurons crisscross like vines in the forest, transmitting signals to different brain regions. Moreover, the projection patterns of neurons are closely related to different brain functions.
Therefore, to understand the working principle of the brain, it is necessary to deeply study the composition and connection of the brain neural network. It is an inevitable choice for brain science research to draw a high-resolution brain neuron connection map, the so-called "brain map".
Vogel Stein said that 50 years have passed, and this is the first "map" of the whole brain of Drosophila. "It is a milestone that proves that we can do this."
The first brain "map" that humans tried to make was that of nematodes, which began in the 1970s and took 14 years.
Since then, some connected maps including fruit flies, mice and even human brains have been drawn one after another, but they all represent only a small part of the "map" of the brain.
The latest published research was completed by researchers from Johns Hopkins University in the United States and Cambridge University in the United Kingdom. The title of this paper is The connectome of an insect brain.
Through continuous slicing, imaging and three-dimensional reconstruction, the researchers finally drew a connection group map containing 3016 neurons and 548,000 synapses.
How to draw the "brain map" of Drosophila?
Albert cardona told 澎湃 Technology that they encountered many difficulties in their research. The research project began in 2010, and it has been a great challenge to pretreat 5,000 continuous 40-nanometer-thick slices of the intact central nervous system of Drosophila melanogaster larvae. Because each slice is fragile, it is easy to be lost or damaged. After pretreatment, imaging them with nanometer resolution requires three transmission electron microscopes to work for six months at the same time, which is another major challenge. After successful imaging, they still need to align hundreds of thousands of separate images to reconstruct all their neurons and synapses in three dimensions and draw all the "circuits" of their whole brain.
The research team deliberately chose Drosophila larvae, because for insects, this species has many basic biological similarities with humans, including similar genetic basis. It also has rich learning and decision-making behaviors, making it a useful model organism in neuroscience.
The research work of Cambridge University and Johns Hopkins University took 12 years. It takes a whole day to image only one neuron.
Researchers at Cambridge University have created high-resolution images of brain neurons, and studied these images to find each individual neuron and strictly track the synaptic connections of each neuron.
From "Insect Brain" to "Human Brain"
"(But this) is just a starting point. Then, a major challenge is to analyze the’ circuit’ of the brain. " Albert cardona said.
Researchers hope that by analyzing the information processing mechanism in Drosophila nervous system, they can inspire a new machine learning architecture and explore the complex functions of human brain, and try to develop a computer program that can simulate human brain thinking in the future.
Albert cardona said that in textbooks, neurons integrate inputs on their dendrites and then transmit signals to other neurons through their axons. But in real life, for the brains of all animal species, whether vertebrates or invertebrates, axons also receive a large number of input synapses, while dendrites often present output synapses. This leads us to divide all neuronal connections into four types: typical axon-dendritic synapses, then axon-axon, dendrite-dendritic, and dendrite-axon. The number of typical synapses is the most, and the number of branch-axis synapses is the least. The characteristics of "circuit" defined by them are obviously different.
After receiving the data from Cambridge University, the research team of Johns Hopkins University spent more than three years analyzing the connectivity of brain neurons, finding the groups of neurons, and then analyzing how information spreads in their brains.
The researchers found that the busiest circuit in this brain is the neurons in the input and output learning center.
On November 28th, 2022, the researchers uploaded the above-mentioned papers to the preprint website bioRxiv, which was published online by Nature for more than three months.
There are hundreds of billions of neurons in the human brain, which are connected with each other to form the most complex network in the world. All our cognition, emotion and decision-making depend on this network.
Muming Poo, the leader of China’s "Brain Project" and an academician of China Academy of Sciences, mentioned in a speech that the goal of brain science research is clear, that is, to clarify the neural basis and working principle of brain function and understand how the brain works; At the same time, I also hope to get some inspiration from the study of the brain, which can simulate the brain and get higher intelligent artificial devices, including intelligent robots.