Electric fields and slow cortical activity

Electrical activity in the brain gives rise to endogenous electric fields, which are the cause of many signals recorded from the nervous system. Electric fields can also be applied from external sources to modulate the excitability of neuronal populations in both research and clinical settings. I use a brain slice model to investigate the effects of oscillating electric fields on cortical networks. A combined approach of voltage-sensitive dye and two-photon calcium imaging techniques provides a detailed view of the spatiotemporal patterns of network activity and its modulation by electric fields. I find that electric fields induce very small polarizations that can generate much larger population events. I find that low extracellular calcium levels facilitate slow oscillatory activity by increasing sodium conductance, and that this confers an increased sensitivity of the network to electric fields. This suggests that electric fields and extracellular calcium levels may act in concert to synchronize cortical networks. And finally, I provide evidence for a novel theory that electric fields influence and reinforce the activation of neuronal ensembles during Up states. Together these results suggest a significant new hypothesis, that the generation of electric fields is an important mechanism in the network activation for consolidating memories during sleep.