For decades, researchers have debated whether Alzheimer's disease starts independently in vulnerable brain regions at different times, or if it begins in one region and then spreads to neuroanatomically connected areas. A new study strongly supports the latter, demonstrating that abnormal tau protein, a key feature of the neurofibrillary tangles seen in the brains of those with Alzheimer's, propagates along linked brain circuits, "jumping" from neuron to neuron.