Some cases are sporadic and some are hereditary.
Ten percent of the population over 65 years has some form of dementia. The convolutions are narrow, the sulci widened. On cut sections, the cortex is thin. The neuritic plaques and neurofibrillary tangles are best visualized in sections stained with silver. These changes occur in the neocortex, but are more numerous in the uncus, hippocampus, amygdala, and nucleus basalis of Meynert.