This thread is a must-read for anyone who is thinking about MD/PhD or is simply curious as to why there are so many crazy people who would willingly submit themselves to such a thing.
https://forums.studentdoctor.net/th...tist-forum-readme-faqs-updated-3-21-10.64282/
It has links to *a lot* of threads for almost any question you might have.
To answer your question: The biggest determinant of what specialty you can go into is clinical metrics by all of the evidence I've seen and anecdotes from just about everyone on the other side of the pipeline. In terms of being "pushed out" (e.g. step not high enough) of certain specialties, if you do real basic science the problems you study will likely be relevant in way more than a single specialty. If you do something *really* specific, well, that's a different story and brings its own challenges. What I've read / heard a lot of physician scientists say is that many of them end up merely putting on their scientist hat and then taking it off and replacing it with their physician hat another day; i.e. their research and clinical practices are not necessarily aligned.
If you want to do something very specific and related to neurosurgery...then you best get into neurosurgery, I guess XD.
IMHO there's no point to the dual degree if you do not want to run a lab. There are a billion other ways to get research training if you do want to "break into" research later. Many of them are not in any way inferior to the PhD path if you want to do something more clinical in nature where the MD training and maybe a fellowship is more than sufficient. The primary downside is that academics and research don't pay and you will have debt from your undergraduate medical training weighing you down but there are loan repayment programs for physicians interested in pursuing clinical and basic research careers. There is also something to be said for pursuing research training after your clinical interests are well defined (i.e. after finishing the MD or residency) and some in the Physician Scientist forum have even argued that the NIH ought to abolish MD/PhD programs entirely and shift more resources to lower the barriers to entry and create more opportunities for junior clinician scientists to kickstart their careers / pay off loans ASAP / sustain funding from early to mid career.
Something I also really suggest doing while at the NIH is talking to actual MD/PhDs actually doing the physician scientist thing. At the NIH they are fairly common and it's a valuable opportunity afforded by the environment to learn more about the path; doing this with MD/PhDs and MD-"only" (I've always found the "only" addition to this funny) physician scientists is what convinced me to do the dual-degree as opposed to something else. Because you are interested in neurosurgery, I especially recommend talking to
this guy. Very excited about what he does, but also very candid and will give you straight answers and advice about your career plans.
also this post is old but also worth a read
http://www.neuronix.org/2011/07/nrmp-puts-out-charting-outcomes-in.html