Functional Brain mapping using ECoG

(electrocorticography)

Keren Rosenberg Seminar computational method March 08

Use of ECoG for identification of functional brain areas

• ECoG stimulations: determine critical location by disrupting the function.

• ECoG recordings: mapping endogenous cortical function, reflecting normal cortical function.

Functionally event results in:

ERP

(Event-related potentials)

ERS

(Event-related

synchronization)

ERD

(Event-related

desynchronization)

phase-locked not phase-locked not phase-locked

Closing eyes and relaxation: increase in alpha (9-12 Hz)

Hand movement: decrease in Mu rhythm

(9-13 Hz )

Real-time functional brain mapping using electrocorticography (ECoG)

Kai J. Miller, Marcel denNijs, Pradeep Shenoy, John W. Miller, Rajesh P.N. Rao and Jeffrey G. Ojemann

NeuroImage (2007)

Aim

• Improving the identification of functional correlates using ECoG recordings.

Copyright ©2007 Society for Neuroscience

Miller, K. J. et al. J. Neurosci. 2007;27:2424-2432

Different analysis techniques:

Method• Using HFB band-pass of 76-200 Hz which is called: “Ҳ

index”

• 8 patients with peri rolandic electrodes

• ECoG: 4 mm diameter, 1 cm inter-electrode spacing

• Amplifier: 0.15-200 Hz

• Data was processed online using BCI2000

Task

• Repeated opening and closing hand for 3-s block and 3-s rest.

• This was repeated 15 times stating with 10 seconds of rest.

• Analysis was only of first 5 blocks.

Data analysis

• X index band-passed

• 80 ms windows Log power of data was calculated

• Mean and SD of the log power were determined for the baseline period.

• For activity period, the baseline was subtracted for each time window.

• Generation of cortical activation map.

Spectogram from a single electrode for 15s hand movement vs. 10s baseline.

Decrease in mu rhythm in hand movement

A reliable increase with function was over the entire 76–200 Hz interval

localized activity for the first 15 s of movement

Offline hand motor area mapping. The bar plots indicate the sum of suprathreshold activity for each electrode.

Averaged difference between movement and baseline in log power in the most responsive electrode

Freq

Mean, superimposed, activation across all 8 patients

30 76 200

Chi Index

Movement vs. baseline- 8 subjects

Real time mappingSupra-threshold activity immediately upon initiation of the handshake ,

Activation of hand sensorimotor cortex throughout the handshake.

Movie

Discussion

• Reliable maps of cortical function can be obtained using the power in the “χ-index .

• The results can be assessed immediately, in real time.

• This method can be applied to clinical and research mapping of human cortex.

However…

• No comparison to other methods such as fMRI or ECoG stimulations.

• Showed correspondence to Intra Operative Stimulations only in 3 subjects.

• Not all of the subjects showed focal pattern of activation.

Case Study

Keren Rosenbergllana PodlipskyDr. Hadas Okon-SingerUri GordonAndrey ZhdanovDr. David PapoProf. Itzhak FriedDr. Talma Hendler

Dr. Kipervasser SvetlanaDr. Fani AndelmanDavid Yosef

Case StudyCase Study

• 21 years old male (T.B) with epilepsy

• No focal lesion

• Pre-surgical multi-modal evaluation:

• fMRI

• ElectroCorticoGraphy (EcoG) stimulations

• EcoG recordings

Internal

External

Simple# # # 2 2 2

Complex

% $ #2 1 3

Paradigm– Finger tapping:

Block design – 12 task blocks – 6 sequences X 3 sec=18 seconds 13 rest blocks

4

8

t(106)p<0.000118

Activation maps of patient T.B

All motor vs. rest

Correspondance between fMRI and Stripes

Group activation map

Internal simple

External simple

EcoG stimulus evoked event related potentials (ERPs)

stimulus onset stimulus onset

SummarySummary

• In the SMA, amplitude differences locked to cue depends on source of planning