Dear mouse:
You overthink about a particular topic, at any one time, because your brain is trying to solve a problem, correct? This is what brains do, try to solve problems.
Try this, if you will: on paper, define the problem. If research is needed, do the research, get the information you need for the purpose of solving this problem. Come up with possible solutions, list pros and cons, all on paper. Attend to the possibility that makes most sense and carry it through.
Limit your thinking to the paper. If a thought appears later, make a note of it. Then incorporate it to your scientific paper.
As you think more, ask yourself: did I already address this, is it already on paper. If it is, then say to yourself: this has already been addressed. Say this again and again as you ruminate over what has already been addressed.
anita