amyloid plaque

n. A deposit of any one of several types of nonfunctional fibrous protein in an organ. Beta- amyloid protein (BAP) forms amyloid plaques in the brain, and especially in the frontal lobe, hippocampus, amygdala, and entorhi- nal cortex, which are characteristic of people over the age of 70 who have reduced brain function. Amyloid plaques in the brain are used as a diagnostic of Alzheimer's disease.