Probing circuit of Papez with stimulation of anterior nucleus of the thalamus and hippocampal evoked potentials

Purpose: Despite documented clinical effectiveness, deep brain stimulation (DBS) therapy for drug-resistant epilepsy rarely yields long-term seizure free outcomes. Methods: This pilot study in five patients investigated circuit of Papez evoked potentials (EPs) using hippocampal sensing during anterior nucleus of the thalamus (ANT) electrical stimulation. We hypothesize that hippocampal EP is a potential biomarker that could be useful for ANT electrode targeting and improving seizure reduction. We obtained bilateral circuit of Papez EPs in five patients with bilateral temporal lobe epilepsy (TLE). The circuit of Papez EPs were measured and assessed by signal amplitude. Volumetric analysis of relevant mesial temporal structures and ANT stimulation analysis was performed on immediate post-implantation images. Results: The patient with the most favorable seizure outcome, which meant long-term seizure reduction greater than 50 % compared to baseline, had strong bilateral EPs and normal hippocampal structure. Conversely, those without clinical benefit with ANT DBS had absent or weak bilateral EPs as well as MRI findings consistent with mesial temporal sclerosis (MTS). Conclusion: The data support the hypothesis that hippocampal EPs with ANT stimulation may be used to as a surrogate marker to probe circuit of Papez and predict ANT DBS efficacy.