Impact of cognitive stimulation on ripples within human epileptic and non-epileptic hippocampus

Milan Brázdil*, Jan Cimbálník, Robert Roman, Daniel J. Shaw, Matt M. Stead, Pavel Daniel, Pavel Jurák, Josef Halámek

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Background: Until now there has been no way of distinguishing between physiological and epileptic hippocampal ripples in intracranial recordings. In the present study we addressed this by investigating the effect of cognitive stimulation on interictal high frequency oscillations in the ripple range (80-250 Hz) within epileptic (EH) and non-epileptic hippocampus (NH). Methods: We analyzed depth EEG recordings in 10 patients with intractable epilepsy, in whom hippocampal activity was recorded initially during quiet wakefulness and subsequently during a simple cognitive task. Using automated detection of ripples based on amplitude of the power envelope, we analyzed ripple rate (RR) in the cognitive and resting period, within EH and NH. Results: Compared to quiet wakefulness we observed a significant reduction of RR during cognitive stimulation in EH, while it remained statistically marginal in NH. Further, we investigated the direct impact of cognitive stimuli on ripples (i.e. immediately post-stimulus), which showed a transient statistically significant suppression of ripples in the first second after stimuli onset in NH only. Conclusion: Our results point to a differential reactivity of ripples within EH and NH to cognitive stimulation.

Original languageEnglish
Article number47
JournalBMC Neuroscience
Issue number1
Publication statusPublished - 25 Jul 2015

Bibliographical note

© 2015 Brázdil et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(, which permits unrestricted use, distribution, and reproduction in any medium,
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  • Epilepsy
  • High-frequency oscillations
  • Hippocampal ripples
  • Human cognition


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