Take my opinions here with a grain of salt; I've been admitted, but I'm not yet a Harvard student.
But as I understand it, pre-med isn't a major (or concentration, in Harvard lingo), it's just a program on the side of your major. Neurobiology
is a prospective major, but neurophysiology isn't. So in this regard, your best bet is to list a concentration that they actually offer so that they know you care enough about the school to at least make sure they offer the major that you want. I had to compromise on my application. I started out wanting to go into computer engineering, but the closest that they offer is computer science. However, after looking deeper into the differentiations between the two, I think computer science is more for me, anyway!
Since you say that you have a strong neuroscience background, my guess would be that it would be in your best interest to apply to neurobiology. They'll see that you have an already established interest that you want to continue. You'd probably have a better chance than if you applied to a less competitive concentration that you weren't as well prepared for.
Again, just my take on things. I have no idea if they establish quotas for majors or what.