Electrical stimulation for cortical mapping reduces the density of high frequency oscillations

Julia Jacobs* (Corresponding Author), Tilin Golla, Malenka Mader, Björn Schelter, Matthias Dümpelmann, Rudolf Korinthenberg, Andreas Schulze-Bonhage

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Background: High frequency oscillations (HFOs, 80-500. Hz) are EEG biomarkers for epileptogenic areas. HFOs are also indicators of disease activity as HFO rates increase after reduction of antiepileptic medication. Electrical stimulation (ES) can be used for diagnostic purposes as well as therapy in patients with refractory epilepsy. This study investigates the occurrence and changes of HFOs during ES in patients with refractory epilepsy. Objective: Analysis of the effects of ES using intracranial ES on the occurrence of epileptic HFOs. Methods: Patients underwent ES for diagnostic purposes. Ripples (80-200. Hz) and fast ripples (200-500. Hz) were visually marked in a baseline EEG segment prior to ES, after each period of ES as well as after the end of ES. In patients in whom ES triggered a seizure a pre- and postictal segment was marked. Rates of HFOs were compared for the different time periods using a Spearman's correlation and Wilcoxon rank sum test (. p<. 0.05). Results: 12 patients with 911 EEG channels were analyzed. Ripple (. r=. -0.42, p<. 0.001) as well as fast ripple (. r=. -0.21, p<. 0.001) rates decreased significantly over the course of stimulation. This phenomenon was not focal over the seizure onset or neighboring contacts but even observed over distant contacts. Conclusions: ES resulted in a gradual decrease of HFO-Rates over time. The decrease of HFOs was not limited to SOZ areas. If HFOs are considered as markers of disease activity the reduction in HFO-rates as a result of intracranial ES has to be interpreted as a reduction of disease activity.

Original languageEnglish
Pages (from-to)1758-1769
Number of pages12
JournalEpilepsy Research
Issue number10
Early online date28 Sept 2014
Publication statusPublished - Dec 2014

Bibliographical note

This study has been supported by grant JA 1725/2-1 of the German Research Foundation.


  • Electrical stimulation
  • Fast ripple
  • Refractory epilepsy
  • Ripple


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