Excerpt from "Pebble in the Sky" 1950 Isaac Asimov

Dr. Affret Shekt explains the Synapsifier

P.52-53 The nervous system in man - and in animals - is composed of neuroprotein material. Such material consists of huge molecules in [a] very precarious electrical balance. The slightest stimulus will upset one, which will right itself by upsetting the next, which will repeat the process until the brain is reached. The brain itself  is an immense grouping of similar molecules which are connected among themselves in all possible ways. Since there are something like ten to the twentieth power (that is, a one with twenty zeros after it) such neuroproteins in the brain, the number of possible [connection] combinations are  of the order of factorial ten to the twentieth power. This is a number so large that if all the electrons and protons in the universe were made universes themselves, and if all the electrons and protons in all of these new universes again were made universes, then [the number of] all the electrons and protons in all the universes so created would still be nothing by comparison.