Assessment of Effect of Vagal Nerve Stimulator (VNS) on Electrocorticograms Recorded by Responsive Neurostimulator (RNS) in Patients With Drug Resistant Epilepsy

This study will investigate whether a Vagal Nerve Stimulator (VNS) causes measurable desynchronization and reduces epileptiform activity, such as spikes and seizures, in electrocorticograms (ECOGs) recorded by a Responsive Neurostimulator (RNS) in patients who have both devices implanted. Specific aims of the study: 1. Evaluate the change in frequency of epileptiform discharges during active VNS stimulation compared to interstimulation baseline periods 2. Evaluate the change in frequency of seizures during active VNS stimulation compared to interstimulation baseline periods 3. Evaluate the change in the number of RNS activations during active VNS stimulation compared to interstimulation baseline periods 4. Evaluate the change in synchronization of background ECoG (electrocorticogram) during VNS stimulation compared to interstimulation baseline periods.