| Low intensity electric fields have been suggested to affect ongoing neuronal activity in both in vitro studies and in human studies. However, the physiological mechanism of how weak electrical fields affect and interact with intact brain activity is not well understood. I performed in vivo extracellular and intracellular recordings from the neocortex of anesthetized rats and extracellular recordings in behaving rats. Electric fields were generated by sinusoid patterns at slow frequency (0.7, 0.8, 1.25 or 1.7 Hz) via electrodes placed on the surface of the skull or the dura. Transcranial electric stimulation (TES) reliably entrained neurons directly in widespread cortical areas, including the hippocampus. The percentage of TES phase-locked neurons increased with stimulus intensity and depended on the behavioral state of the animal. TES-induced voltage gradient, as low as 1 mV/mm at the recording site, was sufficient to phase-bias neuronal spiking. TES-induced effects were rapid to evolve and disappeared quickly after TES-offset. Intracellular recordings showed that both subthreshold and spiking activity of neurons were under the combined influence of TES forced fields and network activity. Our findings suggest that TES in chronic preparations may be used for experimental and therapeutic control of brain activity. |
