PET imaging is adding a new layer of understanding to scientists’ concept of Alzheimer’s disease pathogenesis and progression. At the 14th Human Amyloid Imaging conference, speakers detailed nuances in the relationship between plaques, tangles, and cognitive decline. They also described nascent efforts to tie pathology in specific brain regions to specific behavioral and cognitive symptoms. While HAI featured new data on the pros and cons of various tau tracers in development, the synaptic tracer UCB-J jumped to the fore. It appears to detect synapse loss throughout AD cortex, as well as in other neurodegenerative diseases such as frontotemporal dementia and progressive supranuclear palsy.