By Michael Irving June 02, 2021
A color-coded map of around 4,000 incoming axons connecting to just one neuronGoogle/Lichtman Laboratory
The human brain is the most ridiculously complex computer that’s ever existed, and mapping this dense tangle of neurons, synapses, and other cells is nigh on impossible. But engineers at Google and Harvard have given it the best shot yet, producing a browsable, searchable 3D map of a small section of the human cerebral cortex.
With about 86 billion neurons connecting via 100 trillion synapses, it’s a Herculean task to figure out exactly what each of them does and how those connections form the basis of thought, emotion, memory, behavior and consciousness. Daunting as it may be, though, teams of scientists around the world are rolling up their sleeves and trying to build a wiring diagram for the human brain – a so-called “connectome.”
Last year, researchers at Google and the Howard Hughes Medical Institute paved the way with a fruit fly brain connectome that encompassed about half of the insect’s full brain. Now, Google and the Lichtman Lab at Harvard have released a similar model of a tiny section of the human brain.
The researchers started with a sample taken from the temporal lobe of the human cerebral cortex, measuring just 1 mm3. This was stained for visual clarity, coated in resin to preserve it, and then cut into about 5,300 slices each about 30 nanometers (nm) thick. These were then imaged using a scanning electron microscope, with a resolution down to 4 nm. That created 225 million two-dimensional images, which were then stitched back together into one 3D volume.
Machine learning algorithms scanned the sample to identify the different cells and structures within. After a few passes by different automated systems, human eyes “proofread” some of the cells to ensure the algorithms were correctly identifying them.
The end result, which Google calls the H01 dataset, is one of the most comprehensive maps of the human brain ever compiled. It contains 50,000 cells and 130 million synapses, as well as smaller segments of the cells such axons, dendrites, myelin, and cilia. But perhaps the most stunning statistic is that the whole thing takes up 1.4 petabytes of data – that’s more than a million gigabytes.
Left: a small section of the dataset. Right: A subgraph of neurons, highlighting excitatory neurons in green and inhibitory neurons in red.Google/Lichtman Laboratory
And that’s just a tiny fragment of the whole thing – Google says the sample is just one millionth of the volume of the full human brain. Clearly, it’s going to take a huge amount of work to scale that up, as will finding a way to store the immense data load and develop a way to organize and access it in a useful way.
While the team begins tackling those problems, the H01 dataset is now available online for researchers and curious onlookers to explore. A companion pre-print paper describing the work is also available on bioRxiv.
Source: Google AI Blog
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