Light micrograph of human brain tissue in Alzheimer's disease, showing its main characteristic histological features of neurofibrillary tangles and a senile plaque. Alzheimer's disease is a form of progressive dementia; the brain is smaller than normal, with degenerative changes affecting the frontal and temporal lobes. Neurofibrillary tangles are masses of thickened filaments in the cytoplasm of neurons (nerve cells) - one is clearly visible at centre top. At bottom left of image is a pale senile plaque, appearing as a mass of dark granules around a non-staining amyloid centre. Magnification: x100 at 35mm size.