  Aging associated brain decline often result in some kind of dementia. Even
when this is a complex brain disorder a physical model can be used in order to
describe its general behavior. This model is based in first principles. A
probabilistic model for the development of dementia is obtained and fitted to
some experimental data obtained from the Alzheimer's Disease Neuroimaging
Initiative. It is explained how dementia appears as a consequence of aging and
why it is irreversible.
