A human brain contains around 85 billion neurons (brain cells) and each neuron may have a thousand connections to other neurons. Imagine you could give every inhabitant of New York City a thousand pieces of string and tell them to hand the other end of each piece of string to a thousand other inhabitants, and have each piece of string send two hundred signals per second. Now multiply the city by a factor of ten thousand. That is a model of a human brain. It is often said to be the most complicated thing that we know of in the whole universe.
