some of these oligomers are cleared from the brain. those that are not cleared out clump together with more pieces of beta-amyloid. as more pieces clump togther the oligomers get bigger larger, and the next size up are called "protofibrils" and the next size after that are called fibrils. after a while, these fibrils clump together with other protein molecules, neurons and non-nerve cells floating around in the space between the cells and form what are called plaques.