EEG

1. Functional Brain Signal
Processing: EEG & fMRI
Lesson 1
Kaushik Majumdar
Indian Statistical Institute
Bangalore Center
kmajumdar@isibang.ac.in
M.Tech. (CS), Semester III, Course B50

2. Brain Signal Type
 Functional (EEG, MEG, PET, fMRI)
 Structural (CT, MRI)

3. Motivation to Study EEG
 Monitoring state of consciousness.
 Brain Computer Interface.
 Understanding cognitive processes.
 Monitoring pathological brain conditions.

4. Human Brain or Neocortex
http://en.wikipedia.org/wiki/Human_brain
https://eprints.usq.edu.au/19846/
2/Bashar_2011_whole.pdf

5. Functional Organization:
Brodmann’s Areas
http://en.wikipedia.org/wiki/Human_brain
http://spot.colorado.edu/~dubin/tal
ks/brodmann/brodmann.html

6. Electroencephalogram (EEG)
Acquisition: 10 – 20 System
http://www.ese.wustl.edu/~n
ehorai/research/eegmeg/E
MEG-Overview.html
http://en.wikipedia.org/wiki/10-
20_system_%28EEG%29

7. Channels by Number
Majumdar, IEEE Trans. Biomed. Eng., vol. 56(4), p. 1228 – 1235, 2009.

8. Multi-Channel EEG Signals
http://maxim.ece.illinois.edu/teaching/fall08/

9. Six Layer Cortex
Mountcastle, Brain, 120:701-722, 1997.

10. Cortical Basis of Scalp EEG
Baillet et al., IEEE Sig. Proc. Mag., Nov 2001, p. 16.

11. Head Tissue Layers

12. Forward Problem : Schematic
Head Model
Brain
Skull
Scalp
Source
EEG Channels

13. Source Models
 Dipole Source Model
(parametric model)
 Distributed Source Model
(nonparametric model)

14. Dipole Source Model

15. Distributed Source Model
Majumdar, IEEE Trans. Biomed. Eng., vol. 56(4), p. 1228 – 1235, 2009.

16. Forward Calculation
 Poisson’s equation in the head
p
f
V J






 )
(
Kybic et al., Phys. Med. Biol., vo. 51, p. 1333 – 1346, 2006

17. Published Conductivity Values
Hallez et al., J. NeuroEng. Rehab., 2007, open access.
http://www.jneuroengrehab.com/content/4/1/46

18. 6 Parameter Dipole Geometry
Hallez et al., J. NeuroEng. Rehab., 2007, open access.
http://www.jneuroengrehab.com/content/4/1/46

19. Potential at any Single Scalp
Electrode Due to All Dipoles
r is the position vector of the scalp electrode
rdip - i is the position vector of the ith dipole
di is the dipole moment of the ith dipole

20. Potential at All Scalp Electrodes

21. For N Electrodes, p Dipoles, T
Discrete Time Points

22. Generalization
V = GD + n
G is gain matrix, n is additive noise.

23. EEG Gain Matrix Calculation
For detail of potential calculations see Geselowitz, Biophysical J., 7, 1967, 1-11.

24. Gain Matrix : Elaboration
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25. Nested Head Tissues
Hallez et al., J. NeuroEng. Rehab., 2007, open access.
http://www.jneuroengrehab.com/content/4/1/46
BRAIN SKULL
SCALP

26. Finite Elements Method
Hallez et al., J. NeuroEng. Rehab., 2007, open access.
http://www.jneuroengrehab.com/content/4/1/46

27. Home Work: Loading EEG Data
Files in Computer RAM and
Familiarization
 EEGLAB (needs MATLAB) available at
http://sccn.ucsd.edu/eeglab/
 Sample EEG Data:
http://sccn.ucsd.edu/eeglab/data/headit.html

28. Must Reading
 Baillet, Mosher & Leahy, “Electromagnetic
brain mapping,” IEEE Sig. Proc. Mag., p. 14
– 30, Nov 2001.
 Hallez et al., “Review on solving the forward
problem in EEG source analysis,” J.
Neuroeng. Rehab., open access, available at
http://www.jneuroengrehab.com/content/4/1/
46

29. THANK YOU
This presentation is available at http://www.isibang.ac.in/~kaushik