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Interictal Fast Ripples Recorded from a Dense Microelectrode Array in Human Epileptic Neocortex

Interictal Fast Ripples Recorded from a Dense Microelectrode Array in Human Epileptic Neocortex. Catherine Schevon , MD, PhD; Andrew Trevelyan, PhD; Robert Goodman, MD; Guy McKhann Jr , MD; Charles Schroeder, PhD; Ronald Emerson, MD June, 2009. I. II. III. IV. V. VI. WM.

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Interictal Fast Ripples Recorded from a Dense Microelectrode Array in Human Epileptic Neocortex

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  1. Interictal Fast Ripples Recorded from a Dense Microelectrode Array in Human Epileptic Neocortex Catherine Schevon, MD, PhD; Andrew Trevelyan, PhD; Robert Goodman, MD; Guy McKhannJr, MD; Charles Schroeder, PhD; Ronald Emerson, MD June, 2009

  2. I II III IV V VI WM Multielectrode Array (MEA) NeuroPortTM, CyberkineticsNeurotechnology Systems, Foxboro, MA (now Blackrock Microsystems, Salt Lake City, UT) • Covers 4 x 4 mm area • 96 contacts in a regular 10x10 grid • Depth 1 mm (Layer IV/V) • 400 micron spacing • Active tips 35-75 μm long x 3-5 μm radius • 30K samples/channel/sec • Implanted in epilepsy patients undergoing chronic intracranial EEG recording, in neocortex to be included in resection • Advantages: • Fine spatial/temporal resolution • Regular grid spacing • Limitations: • Records from one small area • One cortical layer per site

  3. “µEEG” iEEG • Microelectrode recording downsampled and aligned with clinical EEG recording • “Macrodischarges” • Correlate with iEEG epileptiform discharges • Appear widespread in µEEG μEEG

  4. “Microdischarges”

  5. 30 ms 40 ms 200 µV 200 µV 50 µV 50 µV 30 µV 30 µV 30 µV 30 µV µEEG µEEG 100-200 Hz HFO associated with a macrodischarge 200-500 Hz 0.8 – 2 kHz µEEG µEEG 100-200 Hz HFO associated with a microdischarge 200-500 Hz 0.8 – 2 kHz 1 second 1 second

  6. Correlation with interictal events Detections/min during sleep and association with paroxysmal µEEG features Percentage of macrodischarges and microdischarges with associated HFOs

  7. Detections by array location

  8. “HFO events” = time period during which one or more HFOs are detected 85% of events were seen at a single channel 40 µV 50 ms

  9. “HFO events” = time period during which one or more HFOs are detected 11% of events occurred on a large scale Almost all were found within the epileptogenic zone (ie not in Patient 1) 80% of these occurred with macrodischarges 40 µV 400 ms

  10. 200 µV 50 ms 50 ms µEEG Site to site differences during a large scale event 100-200 Hz 200-500 Hz 0.8 – 2 kHz µEEG 100-200 Hz 200-500 Hz 0.8 – 2 kHz

  11. Conclusions and Questions • HFOs and microdischarges are distinct phenomena • Evidence of different mechanisms underlying microdischarges and macrodischarges? • Large-scale HFOs • Arise from multiple simultaneous independent generators • Specific markers of the epileptogenic zone? • Selectively detected by sparse sampling or large sensors? • Evidence of an epileptic network? • Are fast ripples a primary event or a secondary local response (eg excitability)?

  12. Co-authors and colleagues Ron Emerson Robert Goodman Guy McKhann, Jr. Charles Schroeder Andrew Trevelyan Allen Waziri Julien Besle Joe Isler Anna Ipata Elana Zion-Golumbic Sara Inati Peter Lakatos Dan Friedman Helen Scharfman Michael Goldberg

  13. Are all HFOs created equal? • Recording characteristics of Neuroport microelectrodes vsmicrowires or depth electrodes • Selective recording from cortical layers IV and V • Use of detection thresholds create the impression of a binary process

  14. HFO rates • Higher HFO rates (overall and max per channel) than seen with microwires or macroelectrodes but avg per channel similar • HFOs more frequent in epileptogenic zone (but N of 1 outside EZ…) • Almost all HFOs had a fast ripple component

  15. HFO duration Filtered 100-500 Hz activity in subset of channels Average of all channels (what a macroelectrode would see?)

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