One cubic millimetre of a human brain is 1.4 petabytes. A brain holds 1,260,000 of them.
A fly's brain has been mapped completely. A fragment of a human one has been mapped completely. Everything between those two facts and a person who outlives their body is arithmetic, engineering, and one question nobody has answered.
In May 2024 a team led by Jeff Lichtman at Harvard and Viren Jain at Google published the reconstruction of a single cubic millimetre of human cerebral cortex. The tissue came from a 45-year-old woman during surgery for epilepsy. It was cut into roughly 5,000 slices, imaged with electron microscopes, and stitched back together by machine learning.
Inside that one cubic millimetre: 57,000 cells, 150 million synapses, and 230 millimetres of blood vessels. The reconstruction occupies 1.4 petabytes — 1,400 terabytes.
The word “fragment” is ironic. A terabyte is, for most people, gigantic, yet a fragment of a human brain — just a minuscule, teeny-weeny little bit of human brain — is still thousands of terabytes.
Jeff Lichtman, Harvard UniversityHarvard Gazette, May 2024
Multiply the one by the other and you get the size of a complete human brain at that resolution.
1,764,000 petabytes. This is multiplication, not prediction — and it is the easy part of the problem.
Three complete brains exist. None of them is ours.
Not models, not simulations — complete wiring diagrams of real nervous systems, reconstructed from real tissue. Each one waited for imaging and computing power that did not exist when the last was finished.
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302
C. elegans
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3,016
Larval Drosophila
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139,255
Adult Drosophila
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57,000
Human cortex, 1 mm³
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86,000,000,000
Human, whole
Bars are logarithmic. On a linear scale the first four would be invisible.
The gap between a fly and a person is roughly 617,000× in neuron count. That sounds impossible until you notice the gap between a roundworm and a fly was 461×, and it took 38 years to cross.
What a scan is not
A connectome is a map of connections. It is the wiring, not the current running through it. Nobody has shown that a static map of synapses is sufficient to reconstitute the thing it belonged to.
Kenneth Miller, a theoretical neuroscientist at Columbia, has argued the doubt plainly: the brain runs on the dynamics of electrical and biochemical exchange between neurons, and capturing those in a single frozen state may simply not be enough. That objection has not been answered. It has not really been tested either.
There is also the obvious problem. Every complete connectome so far was produced from tissue that was sliced. The procedure is not survivable.
Established
The neuron counts. The synapse counts. The 1.4 petabytes. The publication dates. The multiplication. Every figure on this page is in the sources below and takes minutes to check.
Not established
That a scanned connectome can be run. That running it would constitute the person. That any of this arrives on a schedule. Anyone naming a date is guessing, and we are not going to pretend otherwise.
Given the enormous investment put into this project, it was important to present the results in a way that anybody else can now go and benefit from them.
Viren Jain, Google ResearchHarvard Gazette, May 2024
The 1.4 petabytes are public. That is the part of this story most people miss: the map of that cubic millimetre is sitting on a server right now, free, and almost nobody has looked at it.
HUMANSCAN
In September 2026 a real Drosophila connectome — all 139,255 neurons — was loaded into a browser and tied to a market cap. Several thousand people watched it. That was the small version.
HUMANSCAN is a bet on the large one: that the ladder above does not stop at the fly, and that the first human scan will be the most consequential thing that happens to the definition of a person. The token has no claim on the science and funds no laboratory. It is a place to stand while it happens, and a way of keeping score.
Every dispatch from here reports one number: how much of a human brain has been mapped. Today that number is 0.00008%.
Coming soonSources
- Shapson-Coe et al., “A petavoxel fragment of human cerebral cortex reconstructed at nanoscale resolution”, Science, May 2024. science.org
- “The brain, as we’ve never seen it”, Harvard Gazette, May 2024 — source of both quotations on this page. news.harvard.edu
- Dorkenwald et al. / FlyWire, whole-brain connectome of adult Drosophila melanogaster, Nature, 2024. nature.com
- White et al., “The structure of the nervous system of the nematode Caenorhabditis elegans”, Phil. Trans. R. Soc. Lond. B, 1986.