Whoops, sorry I thought I read that you were considering med school as part of your plan. Indeed, for physiology/deco research, you don't need to go to med school. If research is your primary goal, then doing a Ph.D. would be the best route.
My advice on getting research experience for an application to grad school still stands. Graduate programs are also quite competitive, so getting solid research experience as an undergrad is still really important. I don't know anything about the DAN internships, and if deco research is your interest, then doing one would likely provide real benefits. But, keep in mind that internships are often stints where students are given an already developed project and last for a short period of time. In addition to a DAN internship, find a research lab at your University that you find interesting. Ask to get involved as a freshman, make it your home for your time at University, and learn to do research.
What I mean by "learn to do research" is learn all aspects of it. Doing research includes developing a whole suite of skills that enable you to do an experiment. But it also includes: statistics (as
@tursiops said), big data set management, writing manuscripts, writing proposals, dealing with failure, doing literature searches, reading tons of research papers, asking questions, interpreting data, dealing with failure, inventing new tools to answer questions you are interested in, giving public presentations, creating effective data figures, oh, did I mention dealing with failure? I know that failure part sounds negative, but it is a big part of the entire research process. Experiments will fail, manuscripts will get rejected for publication, grants will get denied funding, etc. It's just part of the process and some people don't deal with it well. The last point I'll make about this paragraph is that the skill set you need as a researcher is vast. It's not something you'll learn in a single internship or even degree. These days, a typical path to a research career is: 1) undergrad, 2) Ph.D., 3) 4-6 years of post-doctoral work, 4) job. Numbers 1-3 are all training. For good scientists, #4 continues the learning/training process.