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

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

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

Human Brain or Neocortex 2/Bashar_2011_whole.pdf

Functional Organization: Brodmann’s Areas ks/brodmann/brodmann.html

Electroencephalogram (EEG) Acquisition: 10 – 20 System ehorai/research/eegmeg/E MEG-Overview.html 20_system_%28EEG%29

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

Multi-Channel EEG Signals

Six Layer Cortex Mountcastle, Brain, 120: , 1997.

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

Head Tissue Layers

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

Source Models Dipole Source Model (parametric model) Distributed Source Model (nonparametric model)

Dipole Source Model

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

Forward Calculation Poisson’s equation in the head Kybic et al., Phys. Med. Biol., vo. 51, p – 1346, 2006

Published Conductivity Values Hallez et al., J. NeuroEng. Rehab., 2007, open access.

6 Parameter Dipole Geometry Hallez et al., J. NeuroEng. Rehab., 2007, open access.

Potential at any Single Scalp Electrode Due to All Dipoles r is the position vector of the scalp electrode r dip - i is the position vector of the ith dipole d i is the dipole moment of the ith dipole

Potential at All Scalp Electrodes

For N Electrodes, p Dipoles, T Discrete Time Points

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

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

Gain Matrix : Elaboration

Nested Head Tissues Hallez et al., J. NeuroEng. Rehab., 2007, open access. BRAIN SKULL SCALP

Finite Elements Method Hallez et al., J. NeuroEng. Rehab., 2007, open access.

Home Work: Loading EEG Data Files in Computer RAM and Familiarization EEGLAB (needs MATLAB) available at Sample EEG Data:

Must Reading Baillet, Mosher & Leahy, “Electromagnetic brain mapping,” IEEE Sig. Proc. Mag., p. 14 – 30, Nov Hallez et al., “Review on solving the forward problem in EEG source analysis,” J. Neuroeng. Rehab., open access, available at 46

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