Fig. 2. Burst suppression activity recorded simultaneously with four electrodes in the hippocampus and four electrodes in the prefrontal cortex. The distance between two recording sites in the hippocampus and prefrontal cortex, respectively, was 300 μm. To facilitate easy comparison between different electrodes, hippocampal spikes displaying large amplitudes are marked by vertical bars . The traces show that spontaneous electrical brain activity is highly regular and synchronized between prefrontal cortex and hippocampus.