A groundbreaking project by Harvard University and Google has produced the most detailed map of human brain connections to date. This achievement focuses on a cubic millimetre of the cerebral cortex, extracted from a patient during epilepsy surgery in 2014. Over a decade, a team of biologists and machine-learning experts meticulously analysed this small tissue sample, which contains roughly 57,000 cells and 150 million synapses. Their work marks a significant advancement in brain science, providing an unprecedented level of detail in understanding the brain’s wiring.
The process began with staining the brain tissue using heavy metals, which bind to lipid membranes in cells, making them visible under an electron microscope. The tissue was then embedded in resin and sliced into extremely thin sections, each just 34 nanometers thick. This technique converted a complex 3D problem into a more manageable 2D one, resulting in a colossal dataset of 1.4 petabytes. To piece together these 2D slices into a coherent 3D model, the team utilized machine-learning algorithms developed in collaboration with Google. This involved aligning the images and automatically segmenting the different cell types, although manual adjustments were required to refine the accuracy of these segments.
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