I'd say go after whichever you have the most passion for, which sounds like neuroscience. Dragging your self to a job that you don't like isn't going to be of benefit, whether or not you have MS.

As for doing lab work, I did a lot of that sort of thing over the years, and the MS didn't really put to many limitations on it. Just a couple of years ago I did a week of dissection work in an anatomy research lab and did just fine. A lot of research stuff is done in pairs or groups, so if there is something that your body doesn't allow you to do, usually someone else in your group can do that part.

With love, Erika