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A groundbreaking project from Harvard University and Google has produced the most detailed map of human brain connections to date. The achievement focuses on a cubic millimeter of cerebral cortex, extracted from a patient during epilepsy surgery in 2014. For more than a decade, a team of biologists and machine learning experts meticulously analyzed this tiny tissue sample, which contains about 57,000 cells and 150 million synapses. Their work marks a major advance in brain science, offering an unprecedented level of detail in understanding the brain’s wiring.
Advanced mapping techniques
The process began by staining brain tissue with 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 transformed a complex 3D problem into a more manageable 2D one, resulting in a whopping 1.4 petabytes of data. To stitch these 2D sections together into a coherent 3D model, the team used 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.
Insights and challenges
The resulting map reveals a wealth of information about the brain’s cellular structure. It has identified neurons with more than 50 synapses, a previously overlooked detail that may be crucial to understanding cortical processing. However, the project faces challenges, such as manually verifying the vast amount of data to correct segmentation errors. Some cells, such as unidentifiable ovoid structures and jumbled cells, remain enigmatic. These anomalies could provide new insights, but require further investigation.
Implications for future research
The brain map is now publicly available, opening up new avenues for research. It holds promise for advancing our understanding of mental disorders, such as schizophrenia, and could inspire improvements in AI by mimicking brain function. Future projects include extending this research to whole mouse brains and additional human brain regions, potentially leading to further breakthroughs in neuroscience and related fields.
