I'm currently an undergraduate physics major entering my senior year in Fall 2017. However, I've had a change of interests and I wish to pursue something along the lines of psychology or neuroscience for graduate school. I've only had the scantest formal psychology education, but I do have a 4.0/4.0 overall GPA in my favor (as a different major, but I've also consistently done well in my humanities electives).
How viable is such a transition from the point of view of a potential PhD advisor in these two fields? I know that there is cross-pollination across fields such as physics and engineering, but do PhD programs in neuroscience, for example, offer similar leeway?
PS: I should also mention that I'm an international student studying in the US, and I would also want to do a PhD strictly within the US.