On Apr. 9, 2025, a team of neuro scientists scientists published findings from the Machine Intelligence from Cortical Networks (MICrONS) Project in a collection of ten studies in the Nature family of journals. The (MICrONS) Project has built the most detailed wiring diagram of a mammalian brain to date. The wiring diagram and its data, freely available through the MICrONS Explorer, are 1.6 petabytes in size (equivalent to 22 years of non-stop HD video), and offer never-before-seen insight into brain function and organization of the visual system. 

Scientists at Baylor College of Medicine and Stanford University began by using specialized microscopes to record the brain activity from a one cubic millimeter portion of a mouse’s visual cortex as the animal watched various movies and YouTube clips.

Allen Institute researchers next took that same cubic millimeter of the brain and sliced it into more than 25,000 layers each 1/400th the width of a human hair and used an array of electron microscopes to take high-resolution pictures of each slice.

Finally, another team at Princeton University used artificial intelligence and machine learning to reconstruct the cells and connection into a 3D volume. Combined with the recordings of brain activity, the result is the largest wiring diagram and functional map of the brain to date, containing more than 200,000 cells, four kilometers of axons – the branches that reach out to other cells, and 523 million synapses – the connection points between cells. 

The findings from the studies reveal new cell types, characteristics, organizational and functional principles, and a new way to classify cells. Among the most surprising findings was the discovery of a new principle of inhibition within the brain.

Scientists previously thought of inhibitory cells—those that suppress neural activity—as a simple force that dampens the action of other cells. However, researchers discovered a far more sophisticated level of communication: Inhibitory cells are not random in their actions; instead, they are highly selective about which excitatory cells they target, creating a network-wide system of coordination and cooperation. Some inhibitory cells work together, suppressing multiple excitatory cells, while others are more precise, targeting only specific types. 

The MICrONS Project is a collaborative effort of more than 150 scientists and researchers from the Allen Institute, Princeton, Harvard, Baylor College of Medicine, Stanford and many others.