PhD Scientific Days 2023

Neurosciences - Posters H

Intracortical Mechanisms of After-discharges Elicited by Intracranial 50 Hz Stimulation of Epileptic Patients

Text of the abstract

Introduction: Rhythmic stimulation-induced discharges, known as after-discharges (AD), have long been correlated with epileptogenic processes. Nevertheless, the latent neuronal processes, as well as its exact relationship with the epileptogenic zone (EZ), are still poorly understood.
Aims: Our goal was to delineate spectral characteristics of ADs derived from intracranial macro- and microelectrode recordings, with specific emphasize on differentiating layer-specific activity.
Methods: Our study examines the data of 14 patients undergoing presurgical evaluation with subdural grid electrodes, presenting prominent ADs in the course of a 50 Hz stimulation protocol. Simultaneously, laminar multielectrode arrays (LME) were also implanted in the hypothesized EZ. ADs were visually identified on the macroelectrode recordings of all patients. Spectral characteristics of detected events were compared with AD-free stimulation periods. Six patients with LMEs placed near an AD-presenting electrode (at max. 2 cm distance), were selected for further analysis.
Result: We have examined 36 stimulation epochs containing series of ADs, with overall 551 AD events of both macro- and microelectrode recordings. ADs detected on macroelectrode recordings proved to be very localized, only LMEs located in proximity (<0.5 cm) were able to register visible discharges. We have demonstrated that ADs contain prominent beta and high frequency components, although the frequency pattern of individual events might change over the course of a series. Current-source density (CSD) analysis revealed a marked sink in the infragranular domain, in case of LME recordings closest to the AD foci. Furthermore, there was a significant decrease in multiunit activity (MUA) following stimulation, which correlated with stimulation intensity and primarily engaged upper-middle layers. On the contrary, AD peaks were accompanied by prominent MUA activity, encompassing all LME channels.
Conclusion: In sum, we have described the spectral characteristics and intracortical activation pattern related to ADs, which contribute to the better understanding of the phenomena.
Funding: Hungarian National Research, Development and Innovation Office (2017-1.2.1-NKP-2017-00002).