A measurement in which the number of individuals in a study population that display one or more non-tumorous lesion(s) of the brain at a point in time or develop such lesions within a determined period of time are compared to the total number of individuals in the study population. Often expressed as a percentage but could be expressed as a ratio. A non-tumorous lesion is a localized pathological change in structure of an organ or tissue due to injury or disease, which is not neoplastic in origin; especially one that is circumscribed and well defined. Examples of non-tumorous lesions of the brain would include infarctions, hemorrhages, etc.