a progressive degenerative disease of the brain that leads to dementia. On a cellular level, alzheimers is characterised by unusual helical protein filaments in nerve cells (neurons) of the brain. These odd twisted filaments are called neurofibrillary tangles. On a functional level, there is degeneration of the cortical regions, especially the frontal and temporal lobes, of the brain. The U.S. President Ronald Reagan is said to have alzheimers disease. Named after the german neurologist Alois Alzheimer (1864-1915).