Suminski, Aaron J.

BACKGROUND Medication-refractory essential tremor (ET) patients who undergo MR-guided focused ultrasound or Gamma Knife thalamotomy may experience tremor recurrence, prompting rescue deep brain stimulation (DBS). Yet, the impact of prior ventral intermediate nucleus (VIM) lesioning on DBS targeting, microelectrode recording (MER), and stimulation programming remains uncertain. OBSERVATIONS The authors present 3 ET patients undergoing bilateral DBS for tremor recurrence after thalamotomy. Thalamotomy lesions showed depressed electrophysiological activity versus nonlesioned VIM on MER (p = 0.0397) and required smaller DBS charge density increases for tremor control, suggesting irreversible lesion effects despite tremor recurrence. Tremor recurrence correlated with lesion mislocation; specifically, ablations missed the central VIM (mean 1.8 mm) and decussating dentato-rubro-thalamic tract. For rescue DBS, ventral VIM stimulation yields the greatest tremor reduction, while central VIM stimulation balanced tremor control with adverse effects. LESSONS DBS is a safe, effective rescue treatment for failed thalamotomy without needing to retarget the prior lesion site. The authors advocate for prospective studies of initial DBS targeting 2 mm anterior to standard VIM coordinates, reducing intraoperative readjustment for central VIM stimulation; and initial thalamotomy targeting 1 mm anterior and 1.2–1.5 mm superior to standard coordinates for durable tremor control through ablation of both central and ventral VIM. https://thejns.org/doi/10.3171/CASE25955

Abstract Selective activation of smaller diameter over large diameter nerve fibers represents a broad challenge in the electrical modulation of neural activity for clinical applications. For example, off-target activation of motor nerve fibers has been implicated in several failed vagus nerve stimulation (VNS) clinical trials by precluding achieving current amplitudes sufficient to activate the therapeutically targeted small diameter fibers. In this study, we evaluated the use of high-frequency (HF) stimulation to block unwanted activation of large diameter fibers evoked by traditional low-frequency (LF) VNS in a large animal (swine) model. We demonstrate that HF can eliminate specific unwanted LF-evoked components from neural recordings with high selectivity – along with their associated off-target physiological responses - while preserving the activation of smaller diameter fibers driving intended physiological responses. Conversely, block of the smaller diameter fibers was only observed at HF amplitudes much higher than amplitudes commonly used for HF block clinically. We found that in addition to blocking the LF-evoked compound action potential, lower HF amplitudes also drive asynchronous activity which can easily be overlooked. Only at high amplitudes did HF block LF-evoked activation without concomitant asynchronous activation. These data have numerous implications for existing and future LF and HF block neuromodulation therapies.

Abstract Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, a novel electrode that begins as an uncured, flowable prepolymer that can be injected around a neuroanatomical target to minimize surgical manipulation is developed. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, detailed electrochemical and microscopy characterization of its material properties is performed and the feasibility of using it to stimulate the nervous system electrically in rats and swine is validated. The silicone‐metal‐particle composite performs very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSC C ) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of its simplicity, the Injectrode has the potential to be less invasive, more robust, and more cost‐effective than traditional electrode designs, which could increase the adoption of neuromodulation therapies for existing and new indications.