After World War II, the Pacific island of Guam was taken over by the United States military. In the years that followed, a mysterious, debilitating and incurable brain disease struck increasing numbers of the indigenous Chamorro people, hitting the men especially hard.

The disease, known as lytico-bodig among the Chamorro and ALS-PDC among neurologists, leads to a suite of unpleasant symptoms -- the dementia often suffered by Alzheimer's patients, a slow paralysis usually associated with amyotrophic lateral sclerosis and tremors linked with Parkinson's disease. As the disease became the No. 1 killer of Chamorro adults, researchers from all over the world came to investigate. They tested everything from the purity of the water to the quality of the air, but none of them could find anything to explain the disorders.

Scientists did find that the Chamorros made tortillas with flour ground from the seeds of cycads. The large palmlike plants produce cones with fleshy seeds that contain neurotoxins, but lab rats fed on the flour failed to develop neurological disease. The islanders knew the seeds were toxic and washed them repeatedly before using them. Researchers concluded that the Chamorro were exposed to minimal amounts of toxin. The cause of the brain sickness remained unknown.