IN this issue of Anesthesiology, Pullon et al. provide an elegant description of the fade in information flow over the surface of the brain that accompanies change in behavioral responsiveness with propofol. Using data from 16 volunteers, the authors show that incremental increases in the plasma concentration of propofol are associated with an abrupt change in electroencephalogram (EEG) connectivity with loss and, recovery, of responsiveness. Data were analyzed using Granger Causality, which is a sophisticated statistical approach to analyzing multiple time series of data (such as multiple EEG channels), and asking whether data in one series (e.g., in one EEG channel) can forecast data in another series (e.g., another EEG channel). Perhaps a bit of a misnomer (true causality is not inferred), it asks whether data are temporally related. In this...

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