Figure 1.

Typical progression toward burst suppression (BS) pattern, recorded at the EEG and field potential level as well as intracellularly in a cortical neuron in the suprasylvian gyrus (areas 5–7). A, Under light anesthesia (1.5% isoflurane) neuronal activity is mainly characterized by slow-wave sleep-like (SWS) oscillation dominated by a quasi regular slow rhythm of <1 Hz. B, Application of higher concentrations of isoflurane (2.5%) hyperpolarizes the neuronal membrane potential and accelerates cortical oscillations. Occasionally, this transitory activity is interrupted by short periods of flat EEG (*) that increase in duration and become more frequent. C, The transition period is followed by a stable pattern of BS, which is characterized by long silent periods of flat EEG and occasional bursts of activity. In this and subsequent figures, signals are presented with positive polarity upward.