Effects of bilateral hippocampal electrical stimulation on verbal and visual encoding using standard stimulation parameters: A randomized, double-blind, placebo-controlled crossover study
Abstract number :
3.132
Submission category :
2. Translational Research / 2A. Human Studies
Year :
2025
Submission ID :
1124
Source :
www.aesnet.org
Presentation date :
12/8/2025 12:00:00 AM
Published date :
Authors :
Presenting Author: Sharon Chiang, MD, PhD – University of California, San Francisco
Jennifer Stinson, PhD – Baylor College of Medicine
Adel Hassan, BS – Baylor College of Medicine
Adel Iqbal, BS – Rice University
Jamie Philp, BS – Baylor College of Medicine
Promise Ufomadu, BS – Baylor College of Medicine
Sruthi Karicheri, BS – Baylor College of Medicine
Liam Ferreira, MD, MBA – Baylor College of Medicine
Grace Cardenas, BS – Baylor College of Medicine
Kristen Oliveira, BS – Baylor College of Medicine
Megan Alam, BS – Baylor College of Medicine
Orion Nguyen, BS – Baylor College of Medicine
Vincent Zhang, BS – Baylor College of Medicine
Alica Goldman, MD, PhD – Baylor University
Mohamed Hegazy, MD – Baylor College of Medicine
Sandipan Pati, MBBS – UT Health Houston
Paul Van Ness, MD – Baylor College of Medicine
Lu Lin, MD, PhD – Baylor College of Medicine
Vaishnav Krishnan, MD, PhD – Baylor College of Medicine
Sameer Sheth, MD, PhD – Baylor College of Medicine
Irfan Ali, MD – Baylor College of Medicine
Jay Gavvala, MD – UTHealth Houston
Zulfi Haneef, MBBS MD – Baylor College of Medicine
Rationale: Hippocampal electrical stimulation during active learning has been found to worsen memory in studies employing inpatient intracranial stimulation. However, in more recent studies, intracranial stimulation of the hippocampus has been shown to lead to possible improvements in memory when delivered in response to epileptiform activity in both retrospective and small prospective, predominantly hippocampal, samples. We tested the hypothesis that intracranial stimulation of the bilateral hippocampi using standardized stimulation parameters during active learning would alter verbal and spatial memory performance.
Methods: Intracranial electrodes were implanted in 11 subjects with bilateral hippocampal electrodes as part of clinical treatment for epilepsy with the Responsive Neurostimulation System (RNS). Months following implantation, subjects completed a verbal learning task in which they learned a list of words using the Hopkins Verbal Learning Test, Revised (HVLT-R), and an original visual learning task in which they learned a series of designs that were challenging to verbalize. A randomized, double-blind, placebo-controlled crossover study trial was conducted in which deep-brain electrical stimulation was delivered via the RNS device to bilateral hippocampi using standard electrical stimulation parameters at the time of active learningcompared to sham stimulation. Primary endpoints were the HVLT-R total learning, delayed recall, and recognition. Secondary endpoints were visual total learning and visual delayed recall. For comparison to a non-hippocampal control, effects on verbal and spatial memory was made to a separate group of 9 subjects with neocortical intracranial electrodes implanted with RNS for treatment of epilepsy. Analysis was per-protocol.
Results: Bilateral hippocampal stimulation applied during learning resulted in worsened scores on HVLT-R total learning (median 21, Q1-Q3 18.5-24.8) compared to sham (median 24, Q1-Q3 21-26) (p=0.02). -R recognition hits raw score was seen following bilateral hippocampal stimulation (median 10.5, Q1-Q3 10-11) compared to sham (median 11, Q1-Q3 11-12), although there was no significant difference in HVLT-R discrimination raw scores was present. There were no significant differences in delayed recall or in visual memory measures between stimulation and sham conditions. Neocortical stimulation resulted in no significant change in verbal or visual memory.
Conclusions: Electrical stimulation of the bilateral hippocampus using standard electrical stimulation parameters during verbal learning rning, with no significant impact on delayed recall. In comparison, neocortical stimulation resulted in no significant changes in verbal or visual memory. This may suggest that transient electrical stimulation of the hippocampus during active learning delays enco and that subsequent processes of consolidation and retrieval are less affected.
Funding: None
Translational Research