This keeps me awake at night ... I think of a synapse as a chemical quantum computer. The synapse is about 20 nm. I visualize blowing it up to a box about 10 cm on a side. That's a magnification of 5 million. If I spread out a human cortex flat, it's about 1 m on a side and 3 to 6 cells deep. At this magnification, it's a square 5 km on a side.  The size of a small city. Neurons at this scale are 5 m cubes - room size. We have a kind of city layouts of 3 to 6 story buildings from 15 m to 30 m high. On this scale, we can walk around in our quantum computer like exploring the streets of a city. Under our feet (under street level), we picture te humming and throbbing business of general city maintenance (like waterworks, electricity). That's the brain stem and cerebellum. Essential parts of the brain that we can ignore for the time being. Back to the synapses. Each one is modeled in three parts: the upstream synaptic vesicle (axon), the downstream vesicle (dendrite) and th...

There are  at leas t  100 trillion synapses in the human brain.  For comparison, there are about 1 billion "hosts" (Unique devices) on the internet. So there are 100,000 synapses in  one  brain for all the computers in the world. I compare synapses to "hosts" (computers) rather than "bits" for reasons that will become clear. In theory, a synapse is either "open" (permitting a signal from the "upstream" neuron to pass to the "downstream" neuron) or "closed" (resting or somehow blocking the signal). Call this state variable S=1 or 0 for open or 0 for closed. So one might naively think of the synapse as a "bit" in a computer analog. Every neuron in the brain is only a few synapses away from any other neuron, so one might think that the brain could be like a 100 billion x 100 billion matrix with the synapse "bit" telling whether the signal passes from neuron i to neuron j. That would be a pretty big m...