Three basic questions about thought

Hello, i have three questions about how thought works. I would really appreciate any information on that.

1. Do two different thoughts(for example thinking about pie and about baseball) employ two different sets of neurons or do they employ the same one set of neurons, but in two different ways?

2. Usually a thought is considered to be something like an electric zap in the brain. Is there anything more to it, especially in terms of nourishment, does thinking certain thought imply sending more blood or oxygen or anything else to the certain area of the brain?

3. If a thought continues for a long period of time and only the responsible for it part of the brain is active and nourished, what happens to the rest of the brain cells, do they suffer or atrophy in any way?