A key principle of DHCA is total inactivation of the brain by cooling, as verified by "flatline" isoelectric EEG, also called electrocerebral silence (ECS). Instead of a continuous decrease in activity as the brain is cooled, electrical activity decreases in discontinuous steps. In the human brain, a type of reduced activity called burst suppression occurs at a mean temperature of 24 °C, and electrocerebral silence occurs at a mean temperature of 18 °C. The achievement of measured electrocerebral silence has been called "a safe and reliable guide" for determining cooling required for individual patients, and verification of electrocerebral silence is required prior to stopping blood circulation to begin a DHCA procedure.