MAPT and supranuclear palsy, progressive, 1: Despite relatively similar tau burden, PSP-RS had more atrophy in the midbrain compared with PSP-SL, as already described in past papers,19,24 as well as greater MD and reduced FA in the midbrain, supporting previous papers.25 Indeed, midbrain atrophy has been traditionally considered as the most reliable imaging biomarker supporting a diagnosis of typical PSP,56 with the ‘hummingbird sign’,57 the most commonly used in clinical practice as an adjunct to neurological examination.