Embryonic tissue is prepared. While patients are awake, but sedated, bilateral incisions are made in the skin and burr holes drilled in the skull. A cannula is inserted into the brain to the posterior putamen. Implant patients receive embryonic neural tissue or sham patients have no needles penetrate the brain. After 1 year, patients who receive the sham operation in the first operation may receive embryonic neural tissue in a second operation.