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: ERD (Event-related desynchronization) ERS (Event-related synchronization) ERP (Event-related potentials) not phase-locked phase-locked Hand movement: decrease in Mu rhythm (9-13 Hz) Closing eyes and relaxation: increase in alpha (9-12 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.

Different analysis techniques: Miller, K. J. et al. J. Neurosci. 2007;27:2424-2432 Copyright ©2007 Society for Neuroscience

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.

A reliable increase with function was over the entire 76–200 Hz interval Spectogram from a single electrode for 15s hand movement vs. 10s baseline. Decrease in mu rhythm in hand movement

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.

Movement vs. baseline- 8 subjects Chi Index Freq 30 76 200 Averaged difference between movement and baseline in log power in the most responsive electrode Mean, superimposed, activation across all 8 patients

Real time mapping Supra-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 Rosenberg Dr. Kipervasser Svetlana llana Podlipsky Dr. Hadas Okon-Singer Uri Gordon Andrey Zhdanov Dr. David Papo Prof. Itzhak Fried Dr. Talma Hendler Dr. Kipervasser Svetlana Dr. Fani Andelman David Yosef

Case Study 21 years old male (T.B) with epilepsy No focal lesion Pre-surgical multi-modal evaluation: fMRI ElectroCorticoGraphy (EcoG) stimulations EcoG recordings

Paradigm– Finger tapping: External Internal 2 2 2 # # # Simple 2 1 3 # $ % Complex Block design – 12 task blocks – 6 sequences X 3 sec=18 seconds 13 rest blocks

Correspondance between fMRI and Stripes 4 8 t(106) p<0.000118 Activation maps of patient T.B All motor vs. rest Group activation map

EcoG stimulus evoked event related potentials (ERPs) Internal simple External simple stimulus onset stimulus onset Move to notes: Readiness potentials preceding voluntary movements in the SMA were higher for freely selected movements than for movements in a fixed direction. (Praamstra et al., 1995)

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