Across the long and painful history of neurodegenerative disease, science has largely treated Alzheimer's, Parkinson's, and ALS as separate afflictions with separate fates. A sweeping meta-analysis of 130 brain imaging studies, drawing on data from more than 9,000 individuals, now reveals that beneath their distinct pathologies, all three diseases share a common metabolic signature — a simultaneous energy starvation in the brain's outer cortex and an anomalous overactivity in its deeper structures. The finding reframes neurodegeneration not as a simple dimming of the brain's lights, but as a s