Obviously you can do reflexive research in the interdisciplinary fields which is encouraged by most of the universities. In PHD's there are no particular framework of research that you have to strictly. If your instructor is actively participated in the research which have some connections to the Neurochemistry then you can easily merge your field and your research field to get some amazing research topic out of it. These is in general the phenomenon going all over the world. So if you have the passion and have to legitimate patience of learning a bit of new stuff then definitely you can and you excel.