Brain stimulation for surgical epilepsy

Direct brain stimulation is an emerging treatment of epilepsy especially in patients that are not candidates for epilepsy surgery. Several different approaches of brain stimulation in epilepsy have been developed: stimulation is applied to interrupt epileptic networks in subcortical structures or a stimulus is directly applied to the seizure onset zone. Scheduled stimulation targets mainly subcortical structures like the anterior thalamic nucleus or the centromedian nucleus of the thalamus. The anterior nucleus of the thalamus was studied in a randomized trial in humans. Several case series reported reduction of seizures targeting other subcortical structures. Scheduled stimulation of the seizure onset zone in the hippocampus has also been shown to be safe and effective in a small number of patients. The application of electrical pulses to test for certain brain functions has long been established for the purposes of brain mapping. Traditionally stimulation at 50Hz for several seconds has been used. This stimulus frequently causes afterdischarges or seizures. Afterdischarges can be terminated by applying a very brief stimulus at the same frequency. Responsive stimulation is based on detection on this principle. Seizures are recorded intracranially and a high-frequency pulse applied whenever seizures evolve electrically. An automated implanted device for seizures detection and stimulation has been developed and shown to be safe for human use. A large clinical trial is currently ongoing. In conclusion, the optimal target and mode of stimulation for the treatment of epilepsy remains under investigation and requires large and costly controlled trials.