Interictal fast ripples recorded from a dense microelectrode array in human epileptic neocortex
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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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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


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


“µEEG”

iEEG

  • Microelectrode recording downsampled and aligned with clinical EEG recording

  • “Macrodischarges”

    • Correlate with iEEG epileptiform discharges

    • Appear widespread in µEEG

μEEG


“Microdischarges”


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


Correlation with interictal events

Detections/min during sleep and association with paroxysmal µEEG features

Percentage of macrodischarges and microdischarges with associated HFOs


Detections by array location


  • “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


  • “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


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


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)?


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


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


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


HFO duration

Filtered 100-500 Hz activity in subset of channels

Average of all channels (what a macroelectrode would see?)


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