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
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

slide2
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
slide4
“µEEG”

iEEG

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

μEEG

slide6
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
Correlation with interictal events

Detections/min during sleep and association with paroxysmal µEEG features

Percentage of macrodischarges and microdischarges with associated HFOs

slide9
“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

slide10
“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

slide11
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
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)?
slide13
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
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
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
slide17
HFO duration

Filtered 100-500 Hz activity in subset of channels

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

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