Electrophysiological effects and clinical results of direct brain stimulation for intractable epilepsy

Epilepsy can be considered as a result of the imbalance of the excitatory and inhibitory processes. Therefore, the artificial enhancement of the activity of brain inhibitory mechanisms might lead to a beneficial therapeutic effect for intractable epilepsy patients.

Studies of the inhibitory effects of electrical stimulation of the head of the caudate nucleus (HCN), cerebellar dentate nucleus (CDN), thalamic centromedian nucleus (CM), and neocortical and temporal lobe mesiobasal epileptic foci were performed on 150 patients with implanted intracerebral electrodes. Chronic brain stimulation with implanted neurostimulators was performed on 54 patients. Sixteen were followed up to 1.5 years (mean 1.2 years).

The study demonstrated that 4-8 Hz HCN and 50-100 Hz CDN stimulation suppressed the subclinical epileptic discharges and reduced the frequency of generalized, complex partial, and secondary generalized seizures. CM stimulation (20-130 Hz) desynchronized the EEG and suppressed partial motor seizures. Direct subthreshold 1-3 Hz stimulation of the epileptic focus may suppress rhythmic afterdischarges (ADs). Seizures were eliminated for 26 of 54 patients (48%), worthwhile improvement was achieved for 23 of 54 patients (43%), and no improvement was observed in 5 of 54 patients (9%).

The artificial increase of the activity of brain inhibitory system may suppress the activity of epileptic foci, and, in long run, stabilize this epileptic foci activity at a lower, perhaps normal, level. Therapeutic direct brain stimulation, therefore, might serve as a useful tool in the treatment of intractable and multifocal epilepsy, and might be combined with ablative surgical methods.