Jain says its scale is best understood by thinking of a functional magnetic resonance imaging (fMRI) scan, used to show activity in different brain regions. Read more: Mind’s circuit diagram to be revealed by mammoth mapĪll of this details just a tiny fraction of the brain. They used machine learning to reconstruct the tendrils linking one neuron to another and labelled the different cell types. Finally, they cut it into slices around 30 nanometres thick, or about one-thousandth the width of a human hair, and used an electron microscope to image every slice.Īt this point, Jain’s team at Google took over, assembling the two-dimensional slices – which Jain calls “a deli slicer approach to the brain” – to form a three-dimensional volume. Then they embedded it in resin to toughen it. Lichtman and his team immediately immersed the sample in preservatives, then stained it with heavy metals like osmium, so the outer membranes of every cell were visible under an electron microscope. To do this, the surgeons had to remove some healthy brain tissue that overlaid the hippocampus. She underwent surgery to remove the left hippocampus, the source of her seizures, from her brain. This mammoth undertaking began when a team lead by Jeff Lichtman, also at Harvard University, obtained a tiny piece of brain from a 45-year-old woman with drug-resistant epilepsy. “There’s something just a little emotional about it.” It is the first time we have seen the real structure of such a large piece of the human brain, says Catherine Dulac at Harvard University, who wasn’t involved in the work.

How many neurons are in the brain