For decades, the molecular story of Alzheimer's disease has been told through the proteins science already knew how to find — leaving an entire class of smaller molecules unread, not because they were absent, but because the instruments of inquiry were never calibrated to detect them. Researchers at the Salk Institute have now built the first atlas of microproteins in the human frontal cortex, uncovering more than a thousand previously invisible molecules and tracing at least one of them to the immune cell dysfunction at the heart of Alzheimer's pathology. The work is less a final answer than