In the human brain, neurons don’t communicate directly with each other because they don’t actually touch. Instead they secrete chemical molecules (called neurotransmitters) which travel across the gaps (called synapses). Neurotransmitters can link neurons in an almost infinite amount of ways.
It is in these gaps—the spaces between neurons—that the really important activity of the brain occurs, because it is here that the connections between different parts of the brain occurs.
We cannot even begin to fathom the complexity of the neuro-connections in the brain, for there is probably no other organism in the entire universe as fascinating and complex as the human brain.
In David Brooks fascinating book The Social Animal, Brooks explains that the number of particles in the known universe is about one-tenth of the number of possible interconnection between just 60 neurons in the brains.
Brooks used the growth of a fictional child named Harold to trace the development of the brain during the early stages of life. Here’s what Brooks wrote about the brain of two or three-year old:
“By age two or three, each of Harold’s neurons could have made an average of about 15,000 connections, though the unused ones will get pruned back. Harold could end up with something in the neighborhood of 100 trillion or 500 trillion or even 1,000 trillion synapses. If you want to get a sense of the number of potential connections between the cells in Harold’s brain, contemplate this: A mere 60 neurons are capable of making 1081 possible connections with each other. (That’s 1 with 81 zeroes after it.) The number of particles in the known universe is about one-tenth of this number. Jeff Hawkins suggests a different way to think about the brain. Imagine a football stadium filled with spaghetti. Now imagine it shrunk down to skull size and much more complicated.