How do you choose a specific topic to focus on for approximately 6-12 years?

Was there any exam that you liked a lot to study?
Is there one field where your career would have a better chance at succeeding?
Imagine yourself in 6 years. What kind of life would you be like to live? Work hours, work environment, location. What path would lead you there?
Your professor, do they have an opinion on what you should do, having known you so far?

Talk to professors, people who work in the neuroscience field, job shadow and volunteer in different areas. Talk to other students and see where they could see you, personality tests, career tests, talk to family. Get exposed to an array if specialty areas, and when you find one that makes you feel all warm and fuzzy inside, go after it!

@rinseandrep
My biggest problem is that I won't be taking the more specific courses until next year. And I need to figure out what I want to do this year. My chances of success are all fairly equal in the areas I'm looking at (which is too say a general overview of the psychological aspects of neuroscience). In six years I'll be working on my Masters (hopefully) and that'll be the same regardless of what exactly I choose to study. My prof is pushing rhythms because that's his field.
@nicnac
I can't actually job shadow but I am volunteering in a lab, like I said. I have been talking to my profs that are neuroscientists but it all boils down to what I want and I'm not sure. My family doesn't understand half of what I'm saying these days, like they get the general principle but they just want me to do what is best for me. And the thing is, most of the areas I look at are so exciting. Fascinating. None of them make me "warm and fuzzy" (because I'm not really a warm and fuzzy person) but I could easily see myself doing any of them in the future.