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 fo
r the development of dementia is obtained and fitted to some experimental data obtained from the Alzheimers Disease Neuroimaging Initiative. It is explained how dementia appears as a consequence of aging and why it is irreversible.
