The first comprehensive brain map of a mammalian brain was completed by scientists at Seattle’s Allen Institute for Brain Science. The announcement of the accomplishment was published on April 2, 2014 in the science journal Nature Neuroscience.
Martijn van den Heuvel at the University Medical Center in Utrecht, the Netherlands told New Scientist, “This is a huge leap for modern neuroscience. It will be a reference data set for years of computational neuroscience to come.”
The map details the connections between brain cells called neurons in the mouse brain. According to Discover Magazine, “The tiny mouse brain, for example, contains over 86 million neurons, each with over 1,000 different connections, clustered in different groupings.” Previous attempts at mapping mammal brains show connections between brain regions. This extremely detailed brain map shows the connection between actual brain cells.
In order to create digital maps of mouse brains researchers injected a specific virus that was genetically engineered to be fluorescent green. The virus was injected into a specific part of the living mouse brain. The virus proceeded to infect the neurons near the injection site. After three weeks the virus travels throughout the brain illuminating all seventy-one million neurons and connections.
Once the virus has completed infecting all the neurons in the mouse brain they remove the brain and image it using computers in several different ways. The imaging process generates about one terabyte of data per mouse. As Discover Magazine points out, “researchers collected 1.8 petabytes of data — the equivalent of almost 24 years of continuous high-definition video.” By following the path of the virus they can create a picture of how that particular region connects to the rest of the brain.
The process of actually mapping the brain is explained by New Scientist, “The team diced up each brain into 500,000 pieces each measuring 100 micrometres cubed. Based on the strength of fluorescence in the cubes, they generated a 3D map of how each of the 469 different signals spread through the brain’s thoroughfares and quieter byroads. The result is the most detailed map yet of the mouse brain’s entire neural network.” Researchers analyzed around 1,700 mouse brains total. The report in Nature Neuroscience is based on 469 of them.
The data are already revealing valuable insights about formation of autism and the way mammalian brains process information. Hongkui Zeng and colleagues have already used the data to determine the highly specific connection patterns. They found that the mouse brain features a large number of weak connections and a small number of very strong connections.
“This tells us that the brain integrates information in a very specific, quantitative way,” Zeng told Discover Magazine. “Are these strong and weak connections balancing each other out? Does this enhance the computational power of the brain? This is a very intriguing observation.”