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Epilepsia. 2016 Jan;57(1):111-21. doi: 10.1111/epi.13251. Epub 2015 Nov 26.

Ictal onset patterns of local field potentials, high frequency oscillations, and unit activity in human mesial temporal lobe epilepsy.

Author information

1
Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, U.S.A.
2
Department of Neurosurgery, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, U.S.A.
3
Department of Neurobiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, U.S.A.
4
Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, U.S.A.
5
Brain Research Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, U.S.A.

Abstract

OBJECTIVE:

To characterize local field potentials, high frequency oscillations, and single unit firing patterns in microelectrode recordings of human limbic onset seizures.

METHODS:

Wide bandwidth local field potential recordings were acquired from microelectrodes implanted in mesial temporal structures during spontaneous seizures from six patients with mesial temporal lobe epilepsy.

RESULTS:

In the seizure onset zone, distinct epileptiform discharges were evident in the local field potential prior to the time of seizure onset in the intracranial EEG. In all three seizures with hypersynchronous (HYP) seizure onset, fast ripples with incrementally increasing power accompanied epileptiform discharges during the transition to the ictal state (p < 0.01). In a single low voltage fast (LVF) onset seizure a triad of evolving HYP LFP discharges, increased single unit activity, and fast ripples of incrementally increasing power were identified ~20 s prior to seizure onset (p < 0.01). In addition, incrementally increasing fast ripples occurred after seizure onset just prior to the transition to LVF activity (p < 0.01). HYP onset was associated with an increase in fast ripple and ripple rate (p < 0.05) and commonly each HYP discharge had a superimposed ripple followed by a fast ripple. Putative excitatory and inhibitory single units could be distinguished during limbic seizure onset, and heterogeneous shifts in firing rate were observed during LVF activity.

SIGNIFICANCE:

Epileptiform activity is detected by microelectrodes before it is detected by depth macroelectrodes, and the one clinically identified LVF ictal onset was a HYP onset at the local level. Patterns of incrementally increasing fast ripple power are consistent with observations in rats with experimental hippocampal epilepsy, suggesting that limbic seizures arise when small clusters of synchronously bursting neurons increase in size, coalesce, and reach a critical mass for propagation.

KEYWORDS:

Fast ripple; High frequency oscillation; Hypersynchronous; Limbic seizure; Low voltage fast; Ripple

PMID:
26611159
PMCID:
PMC4862409
DOI:
10.1111/epi.13251
[Indexed for MEDLINE]
Free PMC Article

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