The search criteria consisted of all English language articles published until September 23rd 2019, that contained combinations of “Parkinson,” “cognitive impairment,” “dementia,” “imaging,” “amyloid,” “tau,” “microglia,” “MRI,” and “PET,” The abstracts were screened for relevance, and read in their entirety if they were suitable. The gene discussed is MAPT; the disease is Cognitive impairment.