Evaluation of Direct Effects of Electric Fields on Brain

Transcranial current stimulation (tCS), a safe, tolerable technique employing weak currents (\~ 1 mA) applied to the scalp, has been shown to be a promising technique in alleviating seizures in focal epilepsy patients. Although studies reveal a decrease in the epileptiform activity due to tCS, this field lacks a quantification of neurophysiological changes during and immediately after stimulation. The investigators hypothesise that tCS can effectively reduce the amplitude and rate of interictal spikes as well as the functional connectivity between regions during and immediately after stimulation. It is thus planned to deliver an extensive quantitative description of the tCS effects on interictal spike activity, functional connectivity and other tissue biomarkers, using the simultaneous recording of intracranial signals during tCS. Moreover, the investigators seek to compare these variations between different tCS paradigms (direct current -tDCS- vs alternate current -tACS- stimulation).