I've seen people tightly focused on a problem, in a state of 'flow' and when you break out of it there seems to be a couple of seconds of confusion when they adjust to the circumstances at hand. It is almost as if there is only blood flow, or electrical activity to one part of the brain, and other parts of the brain are dormant.
Sometimes I see this with people who are doing computer programming and drinking coffee.
My question is: What evidence is there for a correlation between being tightly focused on a problem and only using one part of your brain?