UC Irvine

Anesthesia is common in research and clinical settings, but its effect on neural activity is not well understood. Particularly within burst suppression, characterized by quiescent and active periods of the electroencephalogram (EEG), little has been reported about varying levels of anesthesia. We sought to explore this state using bilateral, multi-modal cortical recordings from adult rats under various levels of isoflurane-induced anesthesia. Specifically, we used a multi-sensor microelectrode to record spike trains and local field potentials from the right cortical hemisphere and screw electrodes to record intracranial EEG (iEEG) from the left hemisphere. We investigated action potential firing rate, spike classification, and both temporal correlation and connectivity between spike train and cross-hemisphere iEEG.

Our study shows that a spike train in the right hemisphere is nearly perfectly correlated with EEG in the left hemisphere across all data sets. We see that the same spike classes, i.e. putative neurons are largely active regardless of the level of anesthesia. We demonstrate as anesthesia is increased and thus the EEG is more suppressed, the rate of action potential firing increases while active, even though the total number of action potentials over the entire recording drops. Finally, we show that connectivity is high during burst suppression, and generally becomes stronger as the level of supplied anesthesia increases. These results demonstrate powerful bilateral synchrony and robust neural networks during burst suppression and strong correlation of single neuron activity with emergent behavior. This not only elucidates the neural circuits present during isoflurane-induced anesthesia, it may also have relevance for studies of pathological conditions involving burst suppression, and provide a reference point for studies of electrophysiological signals at multiple scales under all brain states.