A variety of chronic, relatively low-grade injuries to the brain occur in Alzheimer's disease (AD). The extent to which each of these contributes to the clinical syndrome is unclear. Several of the abnormalities that occur in AD brain can cause dementia by themselves, even in people who do not have the neuropathological hallmarks of AD. Prominent among these abnormalities is a deleterious "mitochondrial spiral," which consists of reduced brain metabolism, oxidative stress, and calcium dysregulation. The hypothesis presented in this paper is that the mitochondrial spiral contributes to dementia in AD and presents a reasonable target for the development of new approaches to the treatment of this syndrome.