This image came from the most detailed map of human brain tissue ever produced, a collaborative project between Google and Harvard researchers that took over a decade to complete.
The sample they worked with was a cubic millimetre of human brain tissue. One cubic millimetre. A grain of sand is larger. Inside that fragment, researchers identified 57,000 individual cells, 150 million synapses, and nearly 1.4 kilometres of nerve fibres, all mapped in three dimensional detail at nanometre resolution.
The single neuron visible here connects to 5,600 distinct nerve fibres. That is one cell out of roughly 86 billion in the human brain, each forming thousands of its own connections. The total number of synapses in the human brain is estimated at 100 to 500 trillion.
To put that in context, if you counted one synapse per second without stopping, it would take you over 3 million years to count them all.
The project produced 1.4 petabytes of data from that one cubic millimetre. The entire human brain would require roughly 1.4 zettabytes to map at the same resolution. That is approximately 1,000 times more data than is currently stored across the entire global internet.
One of the unexpected findings was the discovery of a rare but recurring structure where two neurons formed up to 50 connections with each other simultaneously, something never seen before and whose function remains unknown.
The brain you are using to read and understand this sentence contains more connections than there are stars in the Milky Way. It weighs about 1.4 kilograms. It runs on roughly 20 watts of power.
No computer built by humans comes close to its efficiency. No map we have drawn of it is yet complete.
