Insanity; madness; esp. that form which consists in weakness or total loss of thought and reason; mental imbecility; idiocy.
Impairment of many or all higher brain functions; mental deterioration with impaired orientation to time/place/person, along with impaired memory and judgement. Multi-infarct dementia can be caused by a series of strokes.
Deterioration in cognitive and behavioral functioning due to physiological causes.