Low-frequency electrical stimulation of a fiber tract in temporal lobe epilepsy

Abstract

Objective: Surgical resection of the temporal lobe is an effective treatment for medically intractable temporal lobe epilepsy, but can cause memory impairment. Deep brain stimulation in epilepsy has targeted gray matter structures using high frequencies, but achieved limited success. We tested the hypothesis that low-frequency stimulation of the fornix reduces interictal epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy, without affecting memory.

Methods: We implanted depth electrodes in 11 patients for surgical evaluation of intractable epilepsy. Low-frequency stimulation of the fornix occurred in 4-hour sessions in the video-electroencephalography unit. Mental status assessment was performed at baseline and during stimulation. We studied the effect of stimulation on hippocampal spikes and seizures.

Results: There were no complications, and the patients were unaware of the stimulation. Fornix stimulation elicited evoked responses in the hippocampus and the posterior cingulate gyrus. Hourly Mini-Mental Status Examination (MMSE) scores showed an increase during stimulation when compared to prestimulation MMSE, largely due to improvement in recall, possibly representing a practice effect. Hippocampal spikes were significantly reduced during and outlasting each stimulation session. Seizure odds (n = 7) were reduced by 92% in the 2 days that followed stimulation.

Interpretation: Low-frequency stimulation of the fornix activates the hippocampus and other areas of the declarative memory circuit. The results of this preliminary study suggest that low-frequency stimulation is tolerable and reduces epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy. A controlled clinical trial may be warranted.