Spatiotemporal Patterns of High Frequency Oscillation from Intracranial EEG Before and During Seizure

  • Dr Karen Fuller, Department of Clinical Neurosciences, St Vincent's Hospital, Melbourne, Australia
  • Dean Freestone, Department of Electrical and Electronic Engineering, The University of Melbourne, Australia
  • Simon Vogrin, Department of Clinical Neurosciences, St Vincent's Hospital, Melbourne, Australia
  • Alan Lai, The Bionic Ear Institute, Melbourne, Australia
  • Levin Kuhlmann, Department of Electrical and Electronic Engineering, The University of Melbourne, Australia
  • David Grayden, The Bionic Ear Institute, Melbourne, Australia
  • Anthony Burkitt, Department of Electrical and Electronic Engineering, The University of Melbourne, Australia
  • Mark Cook, Department of Clinical Neruosciences, St Vincent's Hospital, Melbourne, Australia

    • Purpose: There is an increasing body of evidence associating high frequency activity on the intracranial electroencephalogram (iEEG), with seizure onset. High frequency discharges or oscillations (HFOs) have been demonstrated to show significant focality. We aim to examine whether the spatiotemporal distribution of bursts of high frequency electrographic activity across intracranial electrode arrays during seizure, accords with postulated seizure spread.

    Method: Continuous iEEG was recorded with sampling rate 4kHz, in patients undergoing routine presurgical assessment. Temporal parameters were obtained from the standard iEEG record and anatomical parameters obtained from neuroradiological coregistration. Seizures were identified on raw data, data was band pass filtered from 100 - 400 Hz and an HFO detector was developed and applied to seizure segments, allowing consideration of spatial and temporal patterns of HFO activity. Directionality of HFOs between maximally active channels around seizure onset was investigated. Diffusion tensor imaging was applied to coregistered images with tractography to visualise potential route of neuronal seizure propagation. Electrode image coordinates were used to calculate direct distances between electrodes of interest.

    Results: Data analysis demonstrated high frequency activity in association with seizure events, within the proposed ictal onset zone, and appearing in channels according with the postulated route of propagation. Patterns of HFO variation were demonstrated prior to seizure onset and during seizure. Their spatiotemporal distribution accorded with standard iEEG and neuroradiologic data.

    Conclusion: The spatiotemporal distribution of high frequency discharges may add to discussion regarding spatiodynamic mechanisms for seizure initiation and propagation.