A study using a new PET imaging agent shows that measures of tau protein in the brain more closely track cognitive decline due to Alzheimer's disease compared with long-studied measures of amyloid beta. More red color indicates more tau protein. The image on the left shows the average tau accumulation in the brains of cognitively normal people, averaged over many individuals. The image on the right shows the average amount of tau buildup in the brains of multiple people with mild Alzheimer's symptoms. Scanning multiple individuals shows that the intensity of tau deposits correlates with the severity of cognitive dysfunction.