Alois Alzheimer (1864-1915). In 1906, German psychiatrist and neuropathologist Alois Alzheimer made a complete clinical and pathological description of presenile dementia, which came to be known as Alzheimer's disease, a progressive condition in which nerve cells in the brain degenerate. Inset image showing PET scans of a normal human brain (right) and one afflicted with Alzheimer's disease (left).