First steps to a comprehensive map of the mouse brain
Francis Crick, a pioneer of molecular biology, once referred to mapping a cubic millimeter of the brain as impossible. It appears the Machine Intelligence from Cortical Networks, MICrONS, Consortium has taken this statement as a challenge. In a series of publications in Nature, they combined live imaging of neuron firing with a 3D reconstruction of a square millimeter of mouse brain to map how the brain responds to a stimulus.
While the brain is composed of many cell types, one in particular is responsible for transmitting signals: the neuron. When a neuron is activated, the cell is flooded with calcium ions. The activated neuron then signals an adjacent neuron to increase its calcium concentration. This electrochemical signal represents the basic mechanism for brain activity. This activity can be tracked live, using calcium imaging, to read how the brain responds to specific stimuli.
The MICrONS Consortium utilized calcium imaging and pupil tracking to measure a mouse’s response to various stimuli. Then, they sliced a portion of the mouse brain into 27,972 slices and used electron microscopy to reconstruct a 1.3 × 0.87 × 0.82 millimeter cube with a resolution of four nanometers; that’s 25,000 times thinner than a human hair. By projecting the live calcium imaging onto the detailed electron-microscope map, they constructed the most accurate model of brain activity to date.
This study is a tremendous step forward in our understanding of how neurons interact with one another, however we are still a long way off to understanding how the whole brain operates. With over 99% of the mouse brain left to map, the MICRrONS Consortium has a long road ahead of them. But having already completed what was once considered impossible, they show no signs of slowing down.
The MICrONS Consortium consists of scientists from Princeton University, Baylor College of Medicine, Johns Hopkins University, Allen Institute for Brain Science, Foundation for Research and Technology Hellas, Massachusetts Institute of Technology, Carnegie Mellon University, Rice University, NSF AI Institute of Artificial and Natural Intelligence, University Tübingen, University Göttingen, Stanford University, University Tübingen, Cornell University, and the Paul Scherrer Institute.
Managing Correspondent: Samuel Lapp
Press Article: An Advance in Brain Research That Was Once Considered Impossible (New York Times)
Original Journal Article: Functional connectomics spanning multiple areas of mouse visual cortex (Nature)
Image Credit: MICrONS Consortium