UC Irvine

The behavior of the brain under general anesthesia remains poorly understood despite the widespread use of anesthesia in medical practice, especially from the electrophysiological standpoint. This thesis studies the relationship between electroencephalographic signals (EEG) and extracellular recordings in the cortex of a rat under different concentrations of isoflurane anesthesia causing burst suppression pattern. EEG signals were recorded from two screw electrodes placed directly on the surface of the brain. The extracellular recordings from which local field potentials (LFPs) and multi-unit activity (MUA) were extracted were recorded from a 7-channel depth electrode. Correlation between different frequency bands of the EEG and firing rate of the recorded neuronal population was assessed at different cortical depths, with the highest correlations being in the theta and high gamma bands. Only 770 out of the 45,121 detected spikes occurred while the EEG was isoelectric, making the EEG bursting a good predictor of the spiking activity. Spike-triggered average and impulse response analysis on both the EEG and LFP signals showed a significant response at the time of the action potential. As anesthesia was increased, the response became stronger, suggesting that functional connectivity, even across hemispheres, is enhanced under isoflurane.