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Epilepsia. 2018 Jul;59(7):1398-1409. doi: 10.1111/epi.14449. Epub 2018 Jun 13.

Ictal and preictal power changes outside of the seizure focus correlate with seizure generalization.

Author information

Department of Neurology, Massachusetts General Hospital, Boston, MA, USA.
Harvard Medical School, Boston, MA, USA.
Department of Mathematics and Statistics, Boston University, Boston, MA, USA.



The treatment of focal epilepsies is largely predicated on the concept that there is a "focus" from which the seizure emanates. Yet, the physiological context that determines if and how ictal activity starts and propagates remains poorly understood. To delineate these phenomena more completely, we studied activity outside the seizure-onset zone prior to and during seizure initiation.


Stereotactic depth electrodes were implanted in 17 patients with longstanding pharmacoresistant epilepsy for lateralization and localization of the seizure-onset zone. Only seizures with focal onset in mesial temporal structures were used for analysis. Spectral analyses were used to quantify changes in delta, theta, alpha, beta, gamma, and high gamma frequency power, in regions inside and outside the area of seizure onset during both preictal and seizure initiation periods.


In the 78 seizures examined, an average of 9.26% of the electrode contacts outside of the seizure focus demonstrated changes in power at seizure onset. Of interest, seizures that were secondarily generalized, on average, showed power changes in a greater number of extrafocus electrode contacts at seizure onset (16.7%) compared to seizures that remained focal (3.8%). The majority of these extrafocus changes occupied the delta and theta bands in electrodes placed in the ipsilateral, lateral temporal lobe. Preictally, we observed extrafocal high-frequency power decrements, which also correlated with seizure spread.


This widespread activity at and prior to the seizure-onset time further extends the notion of the ictogenic focus and its relationship to seizure spread. Further understanding of these extrafocus, periictal changes might help identify the neuronal dynamics underlying the initiation of seizures and how therapies can be devised to control seizure activity.


epileptogenesis; epileptogenic zone; intracranial EEG; partial seizure; temporal lobe epilepsy

[Available on 2019-07-01]
[Indexed for MEDLINE]

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