For a long time, neuroscientists guessed that the human brain contained “about 100 billion neurons” - a number that got passed around so much it became famous. In 2009, a Brazilian researcher named Suzana Herculano-Houzel actually counted them carefully (by literally dissolving brain tissue and counting cells in solution), and the real number turned out to be about 86 billion.
That’s still an unimaginable number. For comparison, our entire Milky Way galaxy contains roughly 100-400 billion stars. Each one of your brain cells, in other words, is roughly equivalent to a star - and they all fit inside your skull.
Even more amazingly, each neuron connects to up to 10,000 others. Multiply that out and you get about 100 trillion connections in a single human brain - more connections than there are galaxies in the observable universe. Every thought, every memory, every sneeze runs through some pattern in that web.
