Functional Brain Signal Processing: Current Trends and Future Directions

1. Functional Brain Signal Processing: Current Trends and Future Directions Kaushik Majumdar Indian Statistical Institute Bangalore Center kmajumdar@isibang.ac.in National Conference on Brain and Consciousness, 20 – 21 September 2013, ISI Kolkata

2. Functional Brain Signals • Two Photon Microscopy • EEG • ECoG • LFP • Single Cell Electrophysiology • MEG • fMRI • PET • SPECT

3. Functional Brain Regions By fundamental premise of deductive science it is to be determined how each area works and how different areas work together, that is, how the areas couple and decouple among themselves. The gold-standard signals are electrophysiological signals from single cells to scalp EEG. http://spot.colorado.edu/~dubin/talks/brodmann/brodmann.html

4. Electrophysiological Signals at Different Scales • Single cell recording • Local filed potential (LFP) • Electrocorticogram (ECoG) • Electroencephalogram (EEG) Buzsaki et al., Nat. Rev. Neurosci., 13: 407 – 420, 2012

5. EEG, LFP, Spikes Buzsaki et al., Nat. Rev. Neurosci., 13: 407 – 420, 2012

6. Information Richness • EEG – least informative, source ambiguous, full of artifacts. • ECoG – mainly excitatory postsynaptic potential in layer VI of the cortex, has less artifacts and more informative than EEG. • LFP – is the most information rich brain signal, superposition of almost all sorts of membrane potentials.

7. Oscillation and Synchrony: Two Major Paradigms for Studying Brain Functions • Oscillating band components in EEG are delta (0 – 4 Hz), theta (4 – 8 Hz), alpha (8 – 12 Hz), beta (12 – 30 Hz) and gamma (30 – 80 Hz). • LFP in mammalian forebrain can oscillate between 0.05 to 500 Hz (Buzsaki & Draguhn, 2004). • Power of oscillation of frequency ƒ varies as ƒ-2.

8. Brain Oscillations (cont.) • The higher the frequency the more confined the oscillation is locally. • The lower the frequency the more widespread the oscillation is.

9. Canolty et al., Science., 313: 1626 – 1628, 2006 Neuronal Oscillation: Functions • Modulates synaptic plasticity. • Influence reaction time. • Correlates with attention. • Modulates perceptual binding. • Coordinate among brain regions far apart. • Consolidate memory.

10. Cortical Oscillation: Frequency Bands • Delta (0 – 4 Hz) • Theta (4 – 8 Hz) • Alpha (8 – 12 Hz), Mu (8 – 12 Hz) • Beta (12 – 30 Hz) • Gamma (30 – 80 Hz) • High gamma (80 – 150 Hz)

11. Canolty et al., Science., 313: 1626 – 1628, 2006 Task Specific Theta – High Gamma Coupling Passive listening to predictable tones Two back phoneme working memory

12. Canolty et al., Science., 313: 1626 – 1628, 2006 Theta – High Gamma Coupling Phase of 4 – 8 Hz (theta) modulates amplitude of 80 – 150 Hz (high gamma).

13. Gray et al., Nature, 338: 334 – 337, 23 March 1989 Neuronal Synchronization

14. linguisticsandbeyond.wordpress.com Broadmann’s Areas

15. Engel et al. Nat. Rev. Neurosci., 2: 704-716, 2001 Binding Problem

16. Phase Synchronization

17. Rodriguez et al., Nature, 397: 430 – 433, 1999 Phase Synchronization in Face Perception

18. Future Challenges • Human depth EEG acquisition. • Different paradigms of cortical computation: a) Neural computation. b) Synaptic computation. c) Dendritic computation. d) Glial computation. • Membrane computation. • Brain-body integration.

19. References • G. Buzsaki, C. A. Anastassiou and C. Koch, The origin of extracellular fields and currents – EEG, ECoG, LFP and spikes, Nat. Rev. Neurosci., 13: 407 – 420, 2012. • X.-J. Wang, Neurophysiological and computaitonal principles of cortical rhythms in cognition, Physiological Rev., 90(3): 1195 – 1268, 2010.

20. THANK YOUThis lecture is available at http://www.isibang.ac.in/~kaushik