Etiquette for returning to do research as grad student in same field as undergrad lab in same institution I'm a medical student planning on taking a year off in the middle to do research. I'm currently at the same intitution as when I was an undergrad (~4 yrs ago) and want to do research in roughly the same area. I did a decent amount of research as an undergrad, all in a single lab. The research area I'm interested in is pretty small and everyone knows each other, regularly does joint journal clubs, etc.

Question: Does it matter if I reach out to the same lab I used to work in? Would it be weird if I did? Would it be rude/inappropriate if I didn't? If I do reach out to a different lab, would it be expected that I ping my old adviser to say I'm back working in research, anyway (so I don't surprise them when I run into them randomly)? Or does none of this matter very much?

I guess I'm just ignorant about the etiquette surrounding stuff like this and was hoping for some clarification. To be clear, I had no problems with my previous lab--I had a good experience and liked my old adviser.
Absolutely not rude or inappropriate, I'm a bit puzzled where you got the suggestion that it might be. There is also nothing wrong with going to a different group. You can certainly let your previous advisor know, and they would be a good reference for you who can speak about your research ability to other professors you are interested in working with, but you don't have any obligation to that professor to only ever work for them.

However, is it normal for people in medical school in your area to take a year off to do research? That part seems a bit more of a potential issue to me. Certainly there are joint research/medical programs (e.g. an MD/PhD in the US), but they typically involve much more than 1 year of research. If this is not a problem where you are, though, then there is nothing wrong with going back to a lab you have positive experience with.

One other thing to consider is whether you could gain some additional breadth of experience in another lab, but this is more about your future goals rather than an issue of what is "appropriate."