In a World First, Researchers Mapped Part of a Mouse’s Brain in Incredible Detail. It’s a Leap Forward for Neuroscience The 3D brain map includes more than 200,000 cells, 523 million synapses and over two miles of axons, representing the most detailed wiring diagram of a piece of mammal brain ever constructed A subset of more than 1,000 neurons, representing just a snapshot of the complexity mapped within a cubic millimeter of mouse brain tissue Allen Institute In 1979, biologist Francis Crick claimed it would be impossible to create an accurate diagram of the brain’s wiring and neuronal activity—even within just a cubic millimeter of brain tissue. Now, a team of more than 150 researchers has proven him wrong by mapping a tiny portion of a mouse’s brain. As detailed in a collection of ten studies published Wednesday in Nature journals, the team of interdisciplinary scientists participating in the Machine Intelligence from Cortical Networks (MICrONS) project have mapped the wiring and visual functions of a piece of mouse brain roughly the size of a grain of sand. This monumental effort represents the most detailed wiring diagram of a mammal brain ever, and it holds important implications for studying brain disorders in humans. “It definitely inspires a sense of awe, just like looking at pictures of the galaxies,” Forrest Collman, a neuroscientist from the Allen Institute and one of the project’s lead researchers, tells the Associated Press’ Lauran Neergaard. “You get a sense of how complicated you are.” The map charts 200,000 cells, 523 million synapses (the connections between neurons) and more than two miles of axons (the part of a neuron that passes on the electrical impulses). All that data adds up to 1.6 petabytes, which is equivalent to about 22 years of continuous, high-definition video, according to a National Institutes of Health statement. “Imagine a kind of Google Maps for the brain, not just showing the major highways, but every small street, every house, every room inside each house and even every door and window,” Collman tells the London Times’ Rhys Blakely. “Just like people use Google Maps to figure out the best route from point A to point B, or even to check if a route exists at all, this kind of detailed brain map lets scientists see whether two neurons are connected and exactly where those connections occur.” Revealing the largest wiring diagram and functional map of the brain Watch on To create the brain map, researchers worked with a lab mouse genetically engineered to make its neurons light up when they fire an electrical signal. They then recorded the brain activity in its visual cortex—the region of its brain associated with vision—as the mouse watched YouTube videos and movie clips, including scenes from Mad Max: Fury Road, The Matrix and the Qatsi experimental documentary trilogy. The researchers then extracted a cubic millimeter of brain tissue and sliced it into roughly 28,000 layers—each about 400 times thinner than a human hair. They photographed each layer, used artificial intelligence to process the images into a digital 3D diagram and combined it with the previously recorded brain activity patterns associated with vision. Because they had studied how the mouse’s neurons lit up as it watched videos, the team could compare the neurons’ mapped structure with their functions and piece together how the connections between them work. While scientists had previously studied brain cells’ structure and function separately, “understanding how neuronal function emerges at the circuit level has been challenging, since we need to study both function and wiring in the same neurons,” Andreas Tolias, a neuroscientist at Baylor College of Medicine and one of the lead researchers, tells Reuters’ Will Dunham. “Our study represents the largest effort to date to systematically unify brain structure and function within a single individual mouse,” he adds. The brain diagram unveiled new cell types, characteristics, relationships and rules of organization and function—and that’s just the start. Researchers also discovered previously unknown complexity in inhibitory cells, or cells that repress brain activity. These cells, they found, are highly selective, targeting specific sets of neurons. Such detailed insight into the brain’s function and structure carries important implications for understanding cognition, as well as how shifts in this wiring might be related to disorders such as Alzheimer’s, autism, Parkinson’s and schizophrenia. “If you have a broken radio and you have the circuit diagram, you’ll be in a better position to fix it,” Nuno da Costa, a biologist at the Allen Institute and one of the project leaders, says in a statement. “In the future, we can use this to compare the brain wiring in a healthy mouse to the brain wiring in a model of disease.” Mouse brains are similar enough to human brains that some of the things we learn from studying their neural circuitry could apply to our own, as Sebastian Seung, a Princeton University neuroscientist involved with the MICrONS project, tells the New York Times’ Carl Zimmer. This might help researchers discover more targeted medications to minimize side effects when treating psychological disorders, he adds. Davi Bock, a neuroscientist from the University of Vermont who was not involved in the project, calls the brain map a “milestone” to the New York Times. He’s associated with another project that last year unveiled the first complete map of an adult fruit fly brain. Bock adds that the scientific advancements that led to this success bring scientists much closer to achieving the next goal: mapping an entire mouse brain. “It’s totally doable, and I think it’s worth doing,” he says. Get the latest stories in your inbox every weekday.