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Keywords:

  • Electrical stimulation;
  • Epilepsy;
  • Hippocampus;
  • Electric fields;
  • CA1;
  • CA3;
  • Ictal

Summary

Purpose: To determine the effects of high-frequency electrical stimulation on electrographic seizure activity during and after stimulation (ON-effect and OFF-effect).

Methods: The modulation and suppression of epileptiform activity during (ON-effect) and after (OFF-effect) high-frequency electrical stimulation was investigated using the high-K+ and picrotoxin hippocampal slice epilepsy models. Uniform sinusoidal fields (50 Hz) were applied with various intensity levels for 1 min across brain slices. Extracellular and intracellular activity were monitored during and after stimulation.

Results: The ON-effects of high-frequency stimulation were highly variable across individual slices and models; ON-effects included modulation of activity, pacing, partial suppression, or activity resembling spreading-depression. On average, epileptic activity, measured as power in the extracellular fields, increased significantly during stimulation. Following the termination of electrical stimulation, a robust poststimulation suppression period was observed. This OFF suppression was observed even at relatively moderate stimulation intensities. The duration of OFF suppression increased with stimulation intensity, independent of ON-effects. Antagonism of GABAAfunction did not directly effect OFF suppression duration.

Conclusions: The present results suggest that “rational” seizure control protocols using intermittent high-frequency electrical stimulation should control for both ON and OFF effects.