LONDON, April 10 (Xinhua) -- Scientists have achieved "a milestone" in neuroscience by constructing the most detailed wiring diagram of a mammalian brain to date, thanks in part to data collected from a mouse as it watched clips from the film "The Matrix."

The high-resolution 3D map, described on Wednesday in a package of eight papers in Nature and Nature Methods, contains over 200,000 brain cells, including approximately 82,000 neurons.

It also identifies more than 500 million synapses, the connection points between neurons, and traces over 4 kilometers of neuronal wiring within a tiny block of tissue from the mouse's visual cortex. This region processes visual information and plays a key role in perception.

A MILESTONE IN CONNECTOMICS

"This brain-activity map, combined with the wiring diagram, marks a milestone in connectomics, a field that aims to show how brains process and organize information," Nature said in an article.

This achievement is the result of more than 150 researchers working on the Machine Intelligence from Cortical Networks (MICrONS) project.

"They managed to do something that we haven't done as a neuroscience community in basically all of our history, which is to be able to map the activity of neurons onto the wiring on a very large population of neurons," says Mariela Petkova, a neuroscientist at Harvard University in Cambridge, Massachusetts, who is not involved with the project. "We have never seen it at this scale."

INNOVATIVE TECHNIQUES

To create the breakthrough map, researchers first recorded the firing of almost 76,000 neurons in the visual cortex of a mouse as the animal watched various videos, including clips from The Matrix, for two hours.

Then the researchers sliced up a cubic millimetre of the mouse's brain into thousands of tissue slices, each about one four-hundredth the width of a human hair.

The scientists imaged each slice and assembled the images into a 3D map. Finally, they used artificial intelligence and machine-learning algorithms to annotate the neurons, their branching projections and their synapses. The team also matched the neurons in the map with their recordings of brain cells in action.

Moritz Helmstaedter, a neuroscientist at the Max Planck Institute for Brain Research in Frankfurt, Germany, says "the combination of function and structure at that scale" is unprecedented. It's "a very impressive endeavour and success."

FUTURE PROSPECTS

The current map covers only 0.2 percent of the mouse's brain, but researchers plan to scale up their techniques to map its entire brain. Their work has already revealed fundamental principles that shape neural circuits in the mouse brain.

The findings add a new wrinkle to a long-held theory in neuroscience: "neurons that fire together wire together."

Previous studies have tested this theory only in limited numbers of neurons and synapses. The current study shows that "there's a diversity [to] how much this rule is applied across all the different components of cortex," says Forrest Collman, a neuroscientist at the Allen Institute for Brain Science in Seattle, Washington, who co-authored the studies.

The MICrONS researchers hope that their data set can help to reveal various features and processes in the brain.

"There are all sorts of cortical areas that we understand at different levels of detail and in different ways. And I think this is really only the beginning of relating structure and function," says Allen Institute neurobiologist Clay Reid, another co-author. Enditem

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