The human brain is so complex that scientific brains find it difficult to give it meaning. A piece of neural fabric the size of a grain of sand could be packed with hundreds of thousands of cells linked by kilometers of wiring. In 1979, Francis Crick, the Nobel Prize scientist, concluded that anatomy and activity in a simple cubic millimeter of brain material would forever exceed our understanding.
“There is no point in asking for the impossible,” said Dr. Crick wrote.
Forty -six years later, a team of more than 100 scientists achieved this impossible, recording cellular activity and mapping the structure in a cubic millimeter of the brain of a mouse – less than one percent of its full volume. By fulfilling this feat, they raised 1.6 data petacts – the equivalent of 22 years of non -stop high definition video.
“This is an important step,” said Davi Bock, a neuroscientist at the University of Vermont who was not involved in the studywhich was published Wednesday in the journal Nature. Dr. Bock said the progress that made it possible to draw a cube millimeter of brain have been invaded well for a new goal: to map the wiring of the whole brain of a mouse.
“It’s totally feasible, and I think it’s worth it,” he said.
Over 130 years passed since the Spanish neuroscientist Santiago Ramón y Cajal first spied on individual neurons under the microscope, making their particular branching forms. Subsequent generations of scientists have developed many details on how a neuron sends a tension peak in a long arm, called axone. Each axon comes into contact with tiny branches, or dendrites, neighboring neurons. Certain neurons excite their neighbors in peaks of tension that draw their own. Some other quiet neurons.
Human thought somewhat emerges from this mixture of excitation and inhibition. But how it happens has remained a huge mystery, largely because scientists could only study a few neurons at the same time.
In recent decades, technological advances have enabled scientists to start mapping the brain in their entirety. In 1986, British researchers published The circuit of a tiny worm, composed of 302 neurons. In the following years, researchers have drawn larger brains, such as the 140,000 neurons in the fly brain.
Could Dr Crick’s impossible dream be possible after all? In 2016, the US government started An effort of $ 100 million To scan a cubic millimeter of a mouse brain. The project – called machine intelligence from cortical networks, or Microns – was led by scientists from the Allen Institute for Brain Science, the University of Princeton and the Baylor College of Medicine.
The researchers focused on a part of the brain of the mouse which receives signals from the eyes and rebuilt what the animal sees. In the first stage of the research, the team recorded the activity of neurons in this region because they showed mouse videos from different landscapes.
The researchers then dissected the brain of the mouse and sprayed the cubic millimeter with hardening chemicals. Then they shaved 28,000 slices of the fabric block, capturing an image of each. Computers have been trained to recognize the contours of cells in each slice and connect the slices together in three -dimensional shapes. All in all, the team has drawn 200,000 neurons and other types of brain cells, as well as 523 million neural connections.
For Nuno Da Costa, biologist of the Allen Institute and one of the project leaders, the simple fact of looking at the cells taking shape on the screen of his computer was breathtaking. “These neurons are absolutely magnificent-that makes me happy,” he said.
To understand how this mesh of the neurons worked, Dr. Da Costa and his colleagues have mapped the activity that had been recorded when the mouse examined the videos.
“Imagine that you are coming to a party that has 80,000 people, and you can be aware of each conversation, but you don’t know who to who,” said Dr. Da Costa. “And now imagine that you have a way to know who to talk to who, but you have no idea what they say. If you have these two things, you can tell a better story about what’s going on.”
By analyzing the data, the researchers have discovered models in the wiring of the brain who had escaped an opinion so far. They have identified distinct types of inhibitory neurons, for example, which are only linked to certain other types of neurons.
“When you are going to study the brain, it seems a little desperate – there are so many connections and so much complexity,” said Mariela Petkova, biophysicist at Harvard who was not involved in the Microns project. “Finding wiring rules is a victory. The brain is much less disorderly than people thought, “she said.
Many microns researchers are now working on a larger project: map the brain with a whole mouse. With a volume of 500 cubic millimeters, a full brain would take decades or centuries to trace current methods. Scientists will have to find additional tips to complete the project in a decade.
“What they have already had to get here is heroic,” said Gregory Jefferis, a neuroscientist at the University of Cambridge, which was not involved in the Microns project. “But we still have a mountain to climb.”
Forrest Collman, member of the Microns project at the Allen Institute, is optimistic. He and his colleagues recently discovered how to make microscopically thin sections from an entire mouse brain. “Some of these obstacles are starting to fall,” said Dr. Collman.
But our own brain, which is about a thousand times larger than that of a mouse, presents a much more important challenge, he added. “The human brain at the moment looks outside the range of what is possible,” he said. “We don’t go away anytime.”
But Sebastian Seung, a neuroscientist of Princeton and a member of the Microns project, noted that the mouse brain and the human brain are similar enough for researchers to glean clues that could help them find drugs to effectively treat psychological disorders without causing harmful side effects.
“Our current methods of manipulation of the nervous system are incredibly frank instruments,” said Dr. Seung. “You have put a medication, and it goes everywhere,” he added. “But being able to really reach and manipulate a type of cell – this is precision.”
The efforts to map a whole mouse brain are supported by financing a long -standing program of the National Institutes of Health Program called the Brain initiative. But the future of effort is uncertain. Last year, Congress reduced the financing of the brain initiative 40%And last month, President Trump signed a 20%reduced bill.
Dr. Bock noted that brain cartography efforts like microns take years, partly because they require the invention of new technologies and software along the way.
“We need consistency and predictability of scientific financing to achieve these long -term goals,” said Dr. Bock.