1. A method of prediction, rapid detection, warning, prevention or control of changes of activity states in the brain of a subject, and of quantifying said changes of activity states, comprising the steps of: (a) receiving into a signal processor input signals indicative of the subject's brain activity; (b) determining at least one ictal component in said input signals by applying to said input signals a first filter configured for extracting and enhancing the at least one ictal component from said input signals; (c) measuring the ictal activity in a foreground epoch of said input signals by applying at least one order-statistic filter to said ictal components corresponding to said epoch to produce a foreground measure of said ictal activity; (d) determining whether said foreground measure reaches a threshold level, such being indicative of the occurrence of a change in activity state in the brain of a subject; (e) quantifying at least one measure of said change in activity state selected from the group consisting of onset location, pattern of spread, intensity, time-frequency evolution, and frequency of occurrence; (f) performing steps (a)-(d) while said change in activity state is occurring and before the onset of electroencephalographic waves of said change in activity state; and (g) analyzing subsequent seizure signal changes to verify that said change in activity state has occurred.