Fig. 6. (  A ) Mean values of Z scores for selected quantitative electroencephalographic features are shown, averaged across 164 patients at different anesthetic states, established with a wide variety of agents to achieve induction and maintain surgical anesthesia. The interpolated topographic maps depict the 19-electrode array of the 10/20 System, looking down on the head, with the anterior regions at the top. The number under each column of maps defines the Z score that corresponds to the corresponding color on the horizontal palette. Induction = on the operating table, counting at the onset of induction; LOC = immediately after loss of consciousness, with loss of responsivity and disappearance of lash reflex due to induction using either thiopental, etomidate, or propofol in approximately equal groups within the sample; surgical plane (SP) = approximately midway during the procedures, with anesthesia under standard procedures primarily maintained by propofol, gas (isoflurane, desflurane, or sevoflurane), or nitrous/narcotic in approximately equal groups within the sample. Note the remarkable similarity of electroencephalographic effects of the different agents used for induction  versus maintenance. ROC = immediately after return of consciousness, when patient first opens eyes on loud command. (  B ) The results of analyses of variance between (induction  vs. LOC) and (SP  vs. ROC) are presented in the two rows of maps of the corresponding F values, indicating that the changes illustrated are highly significant. All Z scores were calculated relative to the reference distributions of the same measures extracted from electroencephalographic recordings obtained from 164 resting patients, before premedication. From John  et al. 121 ; used with permission.