Synchronization between electric fields and neuronal ensembles

The interactions between electromagnetic fields and neuronal tissues have been studied for over a century. Most of these studies have used waveforms with little, or no physiological relevance. In this study I tested the ability of a neuronal ensemble from the CA3 and CA1 to synchronize with an applied electric field, with similar frequency characteristics to that from a real CA3 population burst. Subsequently experiments were conducted where one hippocampal slice produce the electric field input, via population burst firing, to an adjacent hippocampal slice in order to determine if two neuronal ensembles could synchronize their activity through electric fields.; 350 μm thick longitudinal hippocampal slices were prepared from 125–150 gm-Sprague-Dawley rats and perfused at 2ml/min in artificial cerebrospinal fluid (ACSF 3.5 mM KCl). After 90 min the perfusate was changed to one containing 8.5 mM [K]. All experiments were carried out at 34.5–35.1°C. Extracellular field potentials were recorded differentially to the perfusate bath.; The field strength necessary for synchronization to the electric field stimulus was probed. Synchronization was determined using the peri-stimulus-time-histogram; significance was determined with respect to the mean and standard deviation of sham experiments. Population bursts from the CA3 synchronized with the input field at strengths less than 0.8 mV/mm (107 exp. from 13 rats), and activity from small neuronal ensembles of the CA1 synchronized with the input field at strengths less than 0.3 mV/mm (121 exp. from 12 rats). In order to avoid false positive results I used several experimental controls aimed at determining spurious crosscorrelation, including inverting the input field, as well as rotating the slice to look for the appropriate null response.; In an effort to further demonstrate these effects I also looked at extracellular recordings of single unit activity and found that this activity was sensitive to fields down to 0.3 mV/mm (220 exp. from 13 rats). These results illustrate that the limit for electric field interaction is far less than previously demonstrated, and that models of neuronal network synchronization may require consideration of electric field effects. Further study on the interaction between electric fields and neurons is needed.