Light micrograph of human brain tissue in Alzheimer's disease, showing neurofibrillary tangles, masses of thickened filaments in the cytoplasm of neurons (nerve cells). A large tangle appears as the dark mass at centre left. Alzheimer's disease is a form of progressive dementia; the brain is smaller than normal, with degenerative changes affecting the frontal and temporal lobes. In addition to neurofibrillary tangles, the other main histological feature is the formation of senile plaques, which appear as tangled masses of filaments & granules around an amyloid centre. Senile plaques do not feature in this image. Magnification: x130 at 35mm size.