Researchers might have discovered why some people with protein plaques and tangles in their brains do not develop Alzheimer’s disease.

The brains of people without dementia had a buildup of plaques and tangles containing normal tau proteins, while the brains of those with dementia had a different form of tau.

Alzheimer’s may be caused by brain cells’ slowing ability to do proper clean-up, University of California, Riverside, researchers theorized. Tau proteins left too long may change and lead to the development of dementia.