Brain Advance Access published online on February 7, 2008
Brain, doi:10.1093/brain/awn006
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High-frequency oscillations in human temporal lobe: simultaneous microwire and clinical macroelectrode recordings
Department of Neurology, 1Division of Epilepsy and Electroencephalography, 2Division of Child Neurology, Mayo Clinic, Rochester, MN 55905, 3Departments of Neurology and Bioengineering, University of Pennsylvania, Philadelphia, PA 19104 and 4Department of Neurosurgery, Mayo Clinic, Rochester, MN 55905, USA
Correspondence to:
Correspondence to: G. A. Worrell, Department of Neurology, 200 First St. SW, Rochester, MN 55901, USA E-mail: worrell.gregory{at}mayo.edu
Neuronal oscillations span a wide range of spatial and temporal scales that extend beyond traditional clinical EEG. Recent research suggests that high-frequency oscillations (HFO), in the ripple (80–250 Hz) and fast ripple (250–1000 Hz) frequency range, may be signatures of epileptogenic brain and involved in the generation of seizures. However, most research investigating HFO in humans comes from microwire recordings, whose relationship to standard clinical intracranial EEG (iEEG) has not been explored. In this study iEEG recordings (DC – 9000 Hz) were obtained from human medial temporal lobe using custom depth electrodes containing both microwires and clinical macroelectrodes. Ripple and fast-ripple HFO recorded from both microwires and clinical macroelectrodes were increased in seizure generating brain regions compared to control regions. The distribution of HFO frequencies recorded from the macroelectrodes was concentrated in the ripple frequency range, compared to a broad distribution of HFO frequencies recorded from microwires. The average frequency of ripple HFO recorded from macroelectrodes was lower than that recorded from microwires (143.3 ± 49.3 Hz versus 116.3 ± 38.4, Wilcoxon rank sum P<0.0001). Fast-ripple HFO were most often recorded on a single microwire, supporting the hypothesis that fast-ripple HFO are primarily generated by highly localized, sub-millimeter scale neuronal assemblies that are most effectively sampled by microwire electrodes. Future research will address the clinical utility of these recordings for localizing epileptogenic networks and understanding seizure generation.
Key Words: high-frequency oscillations; ripple; fast ripple; intracranial EEG; epilepsy
Abbreviations: HFO, high-frequency oscillations; FR, fast ripples; PSD, power spectral density; SOZ, seizure onset zone
Received August 3, 2007. Revised December 14, 2007. Accepted January 8, 2008.
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