100 - The human brain is a busy place. We each have about 100 billion neurons. Each of the 100 billion neurons actively communicates with 1000 - 10,000 others.
Each of the 100 billion neurons can be 'on' or 'off', and can generate 2100,000,000,000 (or roughly 1030,000,000,000) unique brain states. The number of the possible brain states is greater than the number of particles in the universe!
"Age is strictly a case of mind over matter. If you don't mind, it doesn't matter". By Jack Benny