Figure 1 of our original Article illustrated that treatment with aducanumab reduced human brain amyloid-β plaques in a dose-dependent fashion as measured by florbetapir positron emission tomography (PET) imaging. The figure gave the visual appearance of standard uptake value ratio (SUVR) reduction in subcortical white matter as well as cortical regions, although statistically validated evidence of dose-dependent SUVR reduction was demonstrated only in cortical regions. We provide an updated figure (Fig. 1 of this Addendum), which includes colour bars and difference images to aid in the understanding and interpretation of the representative florbetapir PET images. An additional panel on the right illustrates the differences between baseline and week 54 images, computed by simple subtraction of the baseline from follow-up images, after co-registration to a common coordinate system. The difference images show that the SUVR reduction (which is unitless) occurs primarily in the cortical regions (highlighted in red) in patients treated with aducanumab.