It's like all the processing is in place and each time you enter a topic from a different angle the brain starts fresh, but your open issues/active conlusions are still valid; so, your brain keeps resupplying the same chain of thought. I've done that in meetings and caught myself. It is extra difficult when the chain of thoughts are coming from a flow point.
DS7 does it sometimes and for him or myself, I use humor to break-through (play the Twilight Zone theme in my head.) Or with him "Wait... haven't we been here before? That road sign is looking awfully familiar. Should we ask for directions?"
I'd find a couple of flag words or phrase to help him box off those chains like "Given our previous ideas about Mars.. what do you think about..." or "I was curious if you have new ideas about Mars considering this article." Making notes/writing down thoughts on a topic can also manage them away from the conversation. "Why don't you plan to write out your general thoughts?"
On the other hand, sometimes I need to bring all the systems online relating to a topic before I can switch gears and think about the new thing. And that may mean a complete rehash internally. I'll use stalling phrases like "Huh... need to wrap my head around that..." or "hmm..." or "interesting..." while running through things.
Maybe he's experiencing one or the other or both or it could be something different than what my brain does.
