I am a Freshman in Undergrad and I just started research this semester and I love it. I am volunteering with the Neurology and Anesthesiology department and the skills I’ve learned and projects I’ve been exposed to have been incredible. However, the lab team is huge. There are over 40 Undergraduate volunteers, 8 Graduate students, and 5 Post-Docs working under my PI. So it is very difficult to stand out amongst so many people. I usually work with the graduate students and rarely even see my PI since he is usually working with other head researchers. I plan on committing all 4 years of my undergrad to the lab, but I don’t know how to create a solid relationship with my PI without interrupting him from his work. I will be applying to medical school and, of course, recommendation letters are important so I want to make sure my PI gets to know me well enough to write a valuable letter.
I would really appreciate some advice to best handle this situation, and make the most of my undergraduate research experience.
Thanks 
There is no need to stand out. Just do the work that you are assigned to do as well as you can and it all will pay off. Treat the people on your team with respect, listen to your superiors, follow the proper procedures and all will fall into place. Yes, this is the best way to obtain the great LOR. My D. never dealt with the person in charge of the lab. She just dealt with the graduate student in charge of her project. D. committed to the lab for 3 years, starting with sophomore year and she and her classmates all received great LOR’s and nominations to Phi Beta Kappa from the head of the lab.
Just keep your priorities straight though. Your college GPA, MCAT score are still priority #1, do not loose this prospective.
Best wishes!
As to importance of rec letter from PI: it may/may not be that valuable. It probably depends on which med schools you apply to. Some med schools want/prefer your college’s committee letter, some want a total of 3 (eg, 2 from sci profs who have actually taught you in class and 1 from a non sci prof who has actually taught you in class). And even if med school allows for additional rec letters, just because it comes from a PI in a large Neurology and Anesthesiology department doesn’t mean that every rec letter reader in the country knows of this PI and will automatically attach extra weight to it. And even if it carries some extra weight there are other parts of your application that will be every bit as important (eg GPAs, MCAT, ECs (more clinical in nature), PS, interview, etc). I’m not saying this experience and potential rec letter have no value, but it will be just a part of the bigger picture that your overall application paints.
Given the size of his lab, he probably would never write your letter straight up anyway - no matter how much he liked you. He’ll have either you or someone else (e.g. grad student or post doc who supervises you) write the first draft and just make a few changes here and there and put his name on it. If you are enjoying the lab and learning a lot I would keep at it.