I have been accepted for a Ph.D. in computer science (CS) and funded projects I am applying for are computationally focused whole brain neuroimaging (e.g., MRI, DTI) cognitive neuropsychology research with new experimentally-derived human data. My end goal is to do computational neuroscience at a molecular electrophysiology level using experimentally-derived subject data which my biology, math, and CS background and prior neuro research projects help with (also, would greatly enjoy the positions but end goal strong favorite).
Would doing a Ph.D. with my research in those funded positions (which are more top-down whole brain, as opposed to my bottom-up individual neuron end goal) prohibit me from being a good applicant for postdoc positions in my end goal research area? How much of an extra challenge would this cause compared to doing a Ph.D. directly with research in my end goal?
In general terms: would agreeing to do funded research for a Ph.D. in a related area to the one that is eventually desired allow for getting a postdoc in a position one most wants? Also, what are good ways to do extra work during the degree toward the postdoc wanted?