a method and apparatus to monitor and control the anesthesia state of a patient undergoing general anesthesia is provided . previous automated systems to monitor the anesthesia state of a patient undergoing general anesthesia involve a significant time delay between the patient &# 39 ; s true anesthesia state and the computed indices . the present invention reduces this time delay by using a novel analysis technique applied to spontaneous electrophysiological activity . a transformation and statistical analysis of the observed electrophysiological activity is conducted and compared to reference data to provide numerical indicators . in addition , these indicators are consistent with the levels of depression of patients cns and ans states . this method is illustrated in detail by cns monitoring of electroencephalogram signals .