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It might weigh little over a kilogram but, taken on its own scale, the brain is unimaginably vast. One cubic millimetre contains between twenty and twenty-five thousand neurons. It has eighty-six billion of these cells, and each one is complex as a city and is in contact with ten thousand other neurons just like it. Within just one cubic centimetre of brain tissue, there is the same number of connections as there are stars in the Milky Way. Your brain contains a hundred trillion of them. Information in the form of electricity and chemicals flows around these paths in great forking trails and in circuits and feedback loops and fantastical storms of activity tat bloom to life speeds of up to a hundred and twenty metres per second. According to the neuroscientist V. S. Ramachandran, ‘The number of permutations and combinations of activity that are theoretically possible exceeds the number of elementary particles in the universe.’ And yet, he continues, ‘We know so little about it that even a child’s questions should be seriously entertained.
