The word for today is…
dementia (noun) – Deterioration of intellectual faculties, such as memory, concentration, and judgment, resulting from an organic disease or a disorder of the brain. It is sometimes accompanied by emotional disturbance and personality changes.
Source : The Free Dictionary
Etymology : 1806, from Latin dementia “madness, insanity,” literally “a being out of one’s mind,” from dement-, stem of demens “mad, raving” + abstract noun suffix -ia. It existed earlier in an Englished form, demency (1520s), from French démence. Dementia praecox is a Modern Latin form recorded from 1899 in English, 1891 in German, from French démence précoce (1857).