Electric Field Effects on Brain Activity: Implications for Epilepsy and Burst Suppression

Electric fields are now considered a major mechanism of epileptiform activity. However, it is not clear if another electrophysiological phenomenon, burst suppression, utilizes the same mechanism for its bursting phase. Thus, the purpose of this study was to compare the role of ephaptic coupling-the recruitment of neighboring cells via electric fields-in generating bursts in epilepsy and burst suppression. We used local injections of the GABA-antagonist picrotoxin to elicit epileptic activity and a general anesthetic, sevoflurane, to elicit burst suppression in rabbits. Then, we applied an established computational model of pyramidal cells to simulate neuronal activity in a 3-dimensional grid, with an additional parameter to trigger a suppression phase based on extra-cellular calcium dynamics. We discovered that coupling via electric fields was sufficient to produce bursting in scenarios where inhibitory control of excitatory neurons was sufficiently low. Under anesthesia conditions, bursting occurs with lower neuronal recruitment in comparison to seizures. Our model predicts that due to the effect of electric fields, the magnitude of bursts during seizures should be roughly 2-3 times the magnitude of bursts that occur during burst suppression, which is consistent with our in vivo experimental results. The resulting difference in magnitude between bursts during anesthesia and epileptiform bursts reflects the strength of the electric field effect, which suggests that burst suppression and epilepsy share the same ephaptic coupling mechanism.