Introduction: DBS of the anterior thalamus (ANT) reduces but does not eliminate seizures for epilepsy patients. The mechanism of action remains unknown, and the selection of optimal stimulation parameters is exploratory once standard parameters fail. While periodic pulse (PP) stimulation is the standard, the use of this pattern is mostly performed due to neurostimulator limitations. We trial the effects of non-periodic pulse (NPP) stimulation in comparison to PP for modulating high-frequency oscillations (HFOs) rates.
Methods: Seven patients undergoing stereo-EEG evaluations were enrolled in an IRB-approved protocol involving ANT stimulation. Each patient received both PP and NPP stimulation patterns at two currents (3 mA and 0.5 mA) for 18-minute blocks. Each stimulation block was separated by non-stimulation periods of 18-minutes. HFOs were classified into ripple (R) and fast-ripple (FR) events detected using a matching-pursuit algorithm, with changes in HFO rates calculated within brain regions. Contacts having significant changes were evaluated using KS test between each stimulation condition to aggregate baseline conditions (p < 0.05). Of the contacts achieving statistical significance, the median change in HFO rate was calculated within hippocampus.
Results: Of the 1259 contacts collected across seven patients, 251 contacts in the 3mA, non-periodic and 262 contacts in the 3mA, periodic stimulation were significantly modified from baseline conditions. Of these significant contacts, Hippocampal contacts show a median reduction of 53%, 27%, and 66% of all, R, and FR HFOs for non-periodic high amplitude stimulation (c=36) and 50%, 57%, and 59%, respectively for periodic high amplitude stimulation (c=37).
Conclusion : Results indicate that NPP and PP stimulation produce similar results in the total reduction of HFOs, but NPP selectively produced a greater reduction in FR with less reduction in R compared to PP stimulation within hippocampus. With R being more associated with physiological processing, it could indicate that NPP selectively reduces pathophysiological HFOs while maintaining normal physiological processing.
.jpg)