Effects of continuous bipolar hippocampal deep brain stimulation on memory in patients with unilateral or bilateral...

To evaluate the long-term cognitive and memory outcomes in patients with drug-resistant temporal lobe epilepsy (TLE) treated with continuous hippocampal deep brain stimulation (Hip-DBS), particularly in individuals not eligible for resective surgery.

Nine patients (5 female; mean age 37 years) with drug-resistant TLE underwent unilateral or bilateral Hip-DBS via an occipital trajectory. Patients were selected based on bilateral independent seizure onsets, absence of resectable lesions, or high cognitive functioning. All patients underwent comprehensive pre- and post-operative neuropsychological assessments, including the Wechsler Adult Intelligence Scale (WAIS)/Wechsler Intelligence Scale for Children (WISC), Developmental Neuropsychological Assessment (NEPSY), Wechsler Memory Scale, and Rey Auditory Verbal Learning Test (RAVLT). Follow-up ranged from 24 to 121 months (mean: 68 months). Continuous bipolar stimulation was delivered using anterior hippocampal contacts as cathodes and posterior contacts as anodes.

All patients demonstrated significant seizure reduction; four were seizure-free and five were responders (>80% reduction). No morbidity or mortality occurred. Cognitive outcomes remained stable across the cohort. No significant post-operative decline was observed in full-scale, verbal, or performance IQ or memory performance, regardless of unilateral or bilateral stimulation. One patient, with pre-existing major depression, exhibited cognitive decline and reduced memory scores. However, this was attributed to psychiatric deterioration rather than stimulation effects. Her symptoms stabilized following psychiatric treatment, and DBS was reinitiated without further cognitive decline.

This study provides long-term evidence supporting the cognitive safety and efficacy of continuous Hip-DBS in patients with refractory TLE. Both unilateral and bilateral stimulation were well tolerated, with preserved cognitive and memory function in high-functioning individuals. The findings reinforce the value of Hip-DBS as a non-resective alternative for patients with bilateral or eloquent temporal seizure onsets. Comprehensive psychiatric evaluation and long-term follow-up are critical for optimizing outcomes. Larger, multicenter studies are needed to refine stimulation protocols and better characterize cognitive trajectories.